主线程
- 一个iOS程序运行后，默认会开启1条线程，称为“主线程”或“UI线程”（刷新UI界面最好在主线程中做，在子线程中可能会出现莫名其妙的BUG）
- 主线程的作用
- 显示\刷新UI界面
- 处理UI事件（比如点击事件、滚动事件、拖拽事件等）
- 注意点
- 别将比较耗时的操作放到主线程中
- 耗时操作会卡住主线程，严重影响UI的流畅度，给用户一种“卡”的坏体验
- iOS中多线程的实现方案
- pthread（c语言，程序员管理）
- 一套通用的多线程API
- 适用于Unix\Linux\Windows等系统
- 跨平台\可移植
- 使用难度大
- NSThread（oc语言，程序员管理）
- 使用更加面向对象
- 简单易用，可直接操作线程对象
- GCD（c语言，自动管理）
- 旨在替代NSThread等线程技术
- 充分利用设备的多核
- NSOperation（oc语言，自动管理）
- 基于GCD（底层是GCD）
- 比GCD多了一些更简单实用的功能
- 使用更加面向对象
- pthread（c语言，程序员管理）
NSThread
- 一个NSThread对象就代表一条线程
- 创建、启动线程
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> *thread = [[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> alloc] initWithTarget:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> selector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(run) object:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>]; [thread start]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 线程一启动，就会在线程thread中执行self的run方法</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
- 常见相关用法
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">+ (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> *)mainThread; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得主线程</span> - (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)isMainThread; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 是否为主线程</span> + (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)isMainThread; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 是否为主线程</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获取当前线程</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> *current = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 线程的名字</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setName:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)n; - (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)name;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>
- 其他创建线程方式
- 优点：简单快捷
- 缺点：无法对线程进行更详细的设置
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建线程后自动启动线程</span> [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> detachNewThreadSelector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(run) toTarget:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> withObject:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 隐式创建并启动线程</span> [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> performSelectorInBackground:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(run) withObject:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>
- 控制线程的状态
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 启动线程</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)start; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 进入就绪状态 -> 运行状态。当线程任务执行完毕，自动进入死亡状态</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 阻塞（暂停）线程</span> + (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)sleepUntilDate:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDate</span> *)date; + (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)sleepForTimeInterval:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSTimeInterval</span>)ti; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 进入阻塞状态</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 强制停止线程</span> + (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)exit; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 进入死亡状态</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：一旦线程停止（死亡）了，就不能再次开启任务</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>
互斥锁
- 互斥锁使用格式
<code class="hljs scss has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-at_rule" style="box-sizing: border-box;">@<span class="hljs-function" style="box-sizing: border-box;">synchronized(锁对象)</span> {</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 需要锁定的代码 }</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：锁定1份代码只用1把锁，用多把锁是无效的</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>
原子和非原子属性
- OC在定义属性时有nonatomic和atomic两种选择
- atomic：原子属性，为setter方法加锁（默认就是atomic）
- nonatomic：非原子属性，不会为setter方法加锁
- nonatomic和atomic对比
- atomic：线程安全，需要消耗大量的资源
- nonatomic：非线程安全，适合内存小的移动设备
- iOS开发的建议
- 所有属性都声明为nonatomic
- 尽量避免多线程抢夺同一块资源
- 尽量将加锁、资源抢夺的业务逻辑交给服务器端处理，减小移动客户端的压力
线程间的通信
- 什么叫做线程间通信
- 在1个进程中，线程往往不是孤立存在的，多个线程之间需要经常进行通信
- 线程间通信的体现
- 1个线程传递数据给另1个线程
- 在1个线程中执行完特定任务后，转到另1个线程继续执行任务
- 线程间通信常用方法
<code class="hljs erlang has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-pp" style="box-sizing: border-box;">- <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>performSelectorOnMainThread:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">SEL</span>)</span>aSelector withObject:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(id)</span>arg waitUntilDone:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">BOOL</span>)</span>wait; - <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>performSelector:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">SEL</span>)</span>aSelector onThread:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">NSThread</span> *)</span>thr withObject:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(id)</span>arg waitUntilDone:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">BOOL</span>)</span>wait;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
GCD
- 本质及优点
- 全称是Grand Central Dispatch，可译为“牛逼的中枢调度器”
- GCD会自动管理线程的生命周期（创建线程、调度任务、销毁线程）
- 程序员只需要告诉GCD想要执行什么任务，不需要编写任何线程管理代码
- 使用GCD的步骤
- 定制任务
- 确定想做的事情
- 将任务添加到队列中
- GCD会自动将队列中的任务取出，放到对应的线程中执行
- 任务的取出遵循队列的FIFO原则：先进先出，后进后出
- 定制任务
- 执行任务常用的函数
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 用同步的方式执行任务</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue, dispatch_block_t block); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// queue：队列</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// block：任务</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：使用sync函数往当前串行队列中添加任务，会卡住当前的串行队列。同步方式会阻塞当前队列。</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 用异步的方式执行任务</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue, dispatch_block_t block); dispatch_barrier_async(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue, dispatch_block_t block); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 在前面的任务执行结束后它才执行，而且它后面的任务等它执行完成之后才会执行</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：这个queue不能是全局的并发队列</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>
- 同步和异步的区别
- 同步：只能在当前线程中执行任务，不具备开启新线程的能力
- 异步：可以在新的线程中执行任务，具备开启新线程的能力
- 队列的类型
- 并发队列（Concurrent Dispatch Queue）
- 可以让多个任务并发（同时）执行（自动开启多个线程同时执行任务）
- 并发功能只有在异步（dispatch_async）函数下才有效
- 串行队列（Serial Dispatch Queue）
- 让任务一个接着一个地执行（一个任务执行完毕后，再执行下一个任务）
- 并发队列（Concurrent Dispatch Queue）
- 并发队列
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建并发队列</span> dispatch_queue_t <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">queue</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"队列名称"</span>, DISPATCH_QUEUE_CONCURRENT) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第一个参数 const char *label 队列名称 </span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第二个参数 dispatch_queue_attr_t attr 队列的类型 DISPATCH_QUEUE_CONCURRENT 表示并发队列</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得全局的并发队列</span> dispatch_queue_t <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">queue</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第一个参数 dispatch_queue_priority_t priority 队列的优先级</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第二个参数 unsigned long flags 此参数暂时无用，用0即可</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_HIGH <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 高</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_DEFAULT <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 默认（中）</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_LOW (<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 低</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 后台</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>
- 串行队列
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建串行队列（队列类型传递NULL或者DISPATCH_QUEUE_SERIAL）</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"队列名称"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得主队列，主队列也是串行队列</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_get_main_queue();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>
- 线程间的通信
<code class="hljs r has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">// 从子线程回到主线程
dispatch_async(
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{
// 执行耗时的异步操作<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
dispatch_async(dispatch_get_main_queue(), ^{
// 回到主线程，执行UI刷新操作
});
});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>
- 延迟操作
- iOS中延迟操作有3种
- 调用NSObject的方法
- 使用GCD函数
- 使用NSTimer
- iOS中延迟操作有3种
<code class="hljs r has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">[self performSelector:@selector(run) withObject:nil afterDelay:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span>];
// <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>秒后再调用self的run方法
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span> * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
// <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>秒后执行这里的代码<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
});
[NSTimer scheduledTimerWithTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span> target:self selector:@selector(test) userInfo:nil repeats:NO];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>
- 一次性代码
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 使用dispatch_once函数能保证某段代码在程序运行过程中只被执行1次</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 只执行1次的代码(这里面默认是线程安全的)</span>
});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>
- 快速迭代
<code class="hljs scss has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 使用dispatch_apply函数能进行快速迭代遍历</span>
<span class="hljs-function" style="box-sizing: border-box;">dispatch_apply(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-function" style="box-sizing: border-box;">dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)</span>, ^(size_t index)</span>{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 执行10次代码，index顺序不确定</span>
});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>
- 队列组
- 可以满足的一种需求（当然也可以用依赖线程依赖实现，下文会提到）
- 首先：分别异步执行2个耗时的操作
- 其次：等2个异步操作都执行完毕后，再回到主线程执行操作
- 可以满足的一种需求（当然也可以用依赖线程依赖实现，下文会提到）
<code class="hljs r has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{
// 执行<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>个耗时的异步操作
});
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{
// 执行<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>个耗时的异步操作
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
// 等前面的异步操作都执行完毕后，回到主线程<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>
单例模式
- 单例模式的作用
- 可以保证在程序运行过程，一个类只有一个实例，而且该实例易于供外界访问
- 从而方便地控制了实例个数，并节约系统资源
- 单例模式的使用场合
- 在整个应用程序中，共享一份资源（这份资源只需要创建初始化1次）
- 实现步骤：
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 在.m中保留一个全局的static的实例</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span> _instance;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 重写allocWithZone:方法，在这里创建唯一的实例（注意线程安全），alloc方法会调用allocWithZone:方法</span>
+ (instancetype)allocWithZone:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> _NSZone *)zone
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{
_instance = [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> allocWithZone:zone];
});
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> _instance;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 提供1个类方法让外界访问唯一的实例</span>
+ (instancetype)sharedInstance
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{
_instance = [[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> alloc] init];
});
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> _instance;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 实现copyWithZone:方法</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)copyWithZone:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> _NSZone *)zone
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> _instance;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul>
NSOperation
- NSOperation和NSOperationQueue实现多线程的具体步骤
- 先将需要执行的操作封装到一个NSOperation对象中
- 然后将NSOperation对象添加到NSOperationQueue中
- 系统会自动将NSOperationQueue中的NSOperation取出来
- 将取出的NSOperation封装的操作放到一条新线程中执行
- NSOperation是抽象类，使用NSOperation子类的方式有3种
- NSInvocationOperation
- NSBlockOperation
- 自定义子类继承NSOperation，实现内部相应的方法
- NSInvocationOperation
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建NSInvocationOperation对象</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)initWithTarget:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)target selector:(SEL)sel object:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)arg; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 调用start方法开始执行操作</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)start; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 一旦执行操作，就会调用target的sel方法</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：默认情况下，调用了start方法后并不会开一条新线程去执行操作，而是在当前线程同步执行操作。只有将NSOperation放到一个NSOperationQueue中，才会异步执行操作</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>
- NSBlockOperation
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建NSBlockOperation对象</span> + (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)blockOperationWithBlock:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))block; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 通过addExecutionBlock:方法添加更多的操作</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)addExecutionBlock:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))block; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：只要NSBlockOperation封装的操作数 > 1，就会异步执行操作</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>
- NSOperationQueue
<code class="hljs erlang has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">// 添加操作到<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSOperationQueue</span>中 <span class="hljs-pp" style="box-sizing: border-box;">- <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>addOperation:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">NSOperation</span> *)</span>op; - <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>addOperationWithBlock:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void (^)</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>)block;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
- 相关操作
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 设置最大并发数</span> - (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSInteger</span>)maxConcurrentOperationCount; - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setMaxConcurrentOperationCount:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSInteger</span>)cnt; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 取消队列的所有操作</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)cancelAllOperations; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 提示：也可以调用NSOperation的- (void)cancel方法取消单个操作</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 暂停和恢复队列</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setSuspended:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)b; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// YES代表暂停队列，NO代表恢复队列</span> - (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)isSuspended;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>
- 操作依赖
- NSOperation之间可以设置依赖来保证执行顺序
- 可以在不同queue的NSOperation之间创建依赖关系
<code class="hljs ini has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 102, 102);">[operationB addDependency:operationA]</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; // 操作B依赖于操作A</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>
- 操作的监听
<code class="hljs cs has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 可以监听一个操作的执行完毕</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))completionBlock; - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setCompletionBlock:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))block;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
- 自定义NSOperation
- 只需要重写- (void)main方法，在里面实现想执行的任务
- 注意点
- 自己创建自动释放池（因为如果是异步操作，无法访问主线程的自动释放池）
- 经常通过- (BOOL)isCancelled方法检测操作是否被取消，对取消做出响应
计算时间差
<code class="hljs sql has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">NSDate *<span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">start</span> = [NSDate <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">date</span>];</span> // 上下两句代码间放需要计算时间的程序 NSDate *<span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> = [NSDate <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">date</span>];</span> NSLog(@"%f", [<span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> timeIntervalSinceDate:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">start</span>]);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>
<code class="hljs sql has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">CFTimeInterval <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">begin</span> = CFAbsoluteTimeGetCurrent();</span> // 上下两句代码间放需要计算时间的程序 CFTimeInterval <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> = CFAbsoluteTimeGetCurrent();</span> NSLog(@"%f", <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> - <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">begin</span>);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>
小结：
1、在GCD中，方法如果用异步函数可以开启子线程做事情，该方法中的程序会顺序执行到底，然后再返回去开启子线程执行内部的操作。如果是同步函数，则不能开启子线程，里面的同步函数只能一个一个执行下去。
2、如果在主队列中调用同步函数，容易造成死锁。
- 顶
- 0
时间： 2024-10-09 14:07:16