OC基础(7)

*:first-child {
margin-top: 0 !important; }
body > *:last-child {
margin-bottom: 0 !important; }

a {
color: #4183C4; }
a.absent {
color: #cc0000; }
a.anchor {
display: block;
padding-left: 30px;
margin-left: -30px;
cursor: pointer;
position: absolute;
top: 0;
left: 0;
bottom: 0; }

h1, h2, h3, h4, h5, h6 {
margin: 20px 0 10px;
padding: 0;
font-weight: bold;
-webkit-font-smoothing: antialiased;
cursor: text;
position: relative; }

h1:hover a.anchor, h2:hover a.anchor, h3:hover a.anchor, h4:hover a.anchor, h5:hover a.anchor, h6:hover a.anchor {
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text-decoration: none; }

h1 tt, h1 code {
font-size: inherit; }

h2 tt, h2 code {
font-size: inherit; }

h3 tt, h3 code {
font-size: inherit; }

h4 tt, h4 code {
font-size: inherit; }

h5 tt, h5 code {
font-size: inherit; }

h6 tt, h6 code {
font-size: inherit; }

h1 {
font-size: 28px;
color: black; }

h2 {
font-size: 24px;
border-bottom: 1px solid #cccccc;
color: black; }

h3 {
font-size: 18px; }

h4 {
font-size: 16px; }

h5 {
font-size: 14px; }

h6 {
color: #777777;
font-size: 14px; }

p, blockquote, ul, ol, dl, li, table, pre {
margin: 15px 0; }

hr {
background: transparent url(data:image/png;base64,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) repeat-x 0 0;
border: 0 none;
color: #cccccc;
height: 4px;
padding: 0;
}

body > h2:first-child {
margin-top: 0;
padding-top: 0; }
body > h1:first-child {
margin-top: 0;
padding-top: 0; }
body > h1:first-child + h2 {
margin-top: 0;
padding-top: 0; }
body > h3:first-child, body > h4:first-child, body > h5:first-child, body > h6:first-child {
margin-top: 0;
padding-top: 0; }

a:first-child h1, a:first-child h2, a:first-child h3, a:first-child h4, a:first-child h5, a:first-child h6 {
margin-top: 0;
padding-top: 0; }

h1 p, h2 p, h3 p, h4 p, h5 p, h6 p {
margin-top: 0; }

li p.first {
display: inline-block; }
li {
margin: 0; }
ul, ol {
padding-left: 30px; }

ul :first-child, ol :first-child {
margin-top: 0; }

dl {
padding: 0; }
dl dt {
font-size: 14px;
font-weight: bold;
font-style: italic;
padding: 0;
margin: 15px 0 5px; }
dl dt:first-child {
padding: 0; }
dl dt > :first-child {
margin-top: 0; }
dl dt > :last-child {
margin-bottom: 0; }
dl dd {
margin: 0 0 15px;
padding: 0 15px; }
dl dd > :first-child {
margin-top: 0; }
dl dd > :last-child {
margin-bottom: 0; }

blockquote {
border-left: 4px solid #dddddd;
padding: 0 15px;
color: #777777; }
blockquote > :first-child {
margin-top: 0; }
blockquote > :last-child {
margin-bottom: 0; }

table {
padding: 0;border-collapse: collapse; }
table tr {
border-top: 1px solid #cccccc;
background-color: white;
margin: 0;
padding: 0; }
table tr:nth-child(2n) {
background-color: #f8f8f8; }
table tr th {
font-weight: bold;
border: 1px solid #cccccc;
margin: 0;
padding: 6px 13px; }
table tr td {
border: 1px solid #cccccc;
margin: 0;
padding: 6px 13px; }
table tr th :first-child, table tr td :first-child {
margin-top: 0; }
table tr th :last-child, table tr td :last-child {
margin-bottom: 0; }

img {
max-width: 100%; }

span.frame {
display: block;
overflow: hidden; }
span.frame > span {
border: 1px solid #dddddd;
display: block;
float: left;
overflow: hidden;
margin: 13px 0 0;
padding: 7px;
width: auto; }
span.frame span img {
display: block;
float: left; }
span.frame span span {
clear: both;
color: #333333;
display: block;
padding: 5px 0 0; }
span.align-center {
display: block;
overflow: hidden;
clear: both; }
span.align-center > span {
display: block;
overflow: hidden;
margin: 13px auto 0;
text-align: center; }
span.align-center span img {
margin: 0 auto;
text-align: center; }
span.align-right {
display: block;
overflow: hidden;
clear: both; }
span.align-right > span {
display: block;
overflow: hidden;
margin: 13px 0 0;
text-align: right; }
span.align-right span img {
margin: 0;
text-align: right; }
span.float-left {
display: block;
margin-right: 13px;
overflow: hidden;
float: left; }
span.float-left span {
margin: 13px 0 0; }
span.float-right {
display: block;
margin-left: 13px;
overflow: hidden;
float: right; }
span.float-right > span {
display: block;
overflow: hidden;
margin: 13px auto 0;
text-align: right; }

code, tt {
margin: 0 2px;
padding: 0 5px;
white-space: nowrap;
border: 1px solid #eaeaea;
background-color: #f8f8f8;
border-radius: 3px; }

pre code {
margin: 0;
padding: 0;
white-space: pre;
border: none;
background: transparent; }

.highlight pre {
background-color: #f8f8f8;
border: 1px solid #cccccc;
font-size: 13px;
line-height: 19px;
overflow: auto;
padding: 6px 10px;
border-radius: 3px; }

pre {
background-color: #f8f8f8;
border: 1px solid #cccccc;
font-size: 13px;
line-height: 19px;
overflow: auto;
padding: 6px 10px;
border-radius: 3px; }
pre code, pre tt {
background-color: transparent;
border: none; }

sup {
font-size: 0.83em;
vertical-align: super;
line-height: 0;
}
* {
-webkit-print-color-adjust: exact;
}
@media screen and (min-width: 914px) {
body {
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margin:0 auto;
}
}
@media print {
table, pre {
page-break-inside: avoid;
}
pre {
word-wrap: break-word;
}
}
-->

封装

本小节知识:

  1. 面向对象三大特性
  2. 什么是封装
  3. 为什么要进行封装?

1.面向对象三大特性

  • 封装性
  • 继承性
  • 多态性

2.什么是封装

  • 封装性就是隐藏实现细节，将属性私有化，提供公有方法访问私有属性。

3.为什么要进行封装?

  • 类是数据与功能的封装，数据就是成员变量，功能就类方法或对象方法
  • 对数据的封装，也就是对成员变量的封装
  • 不封装的缺点：当一个类把自己的成员变量暴露给外部的时候,那么该类就失去对该成员变量的管理权，别人可以任意的修改你成员变量。
  • 封装就是将数据隐藏起来,只能用此类的方法才可以读取或者设置数据,不可被外部任意修改是面向对象设计本质。降低了数据被误用的可能性! ，提高代码的灵活性

8

*:first-child {
margin-top: 0 !important; }
body > *:last-child {
margin-bottom: 0 !important; }

a {
color: #4183C4; }
a.absent {
color: #cc0000; }
a.anchor {
display: block;
padding-left: 30px;
margin-left: -30px;
cursor: pointer;
position: absolute;
top: 0;
left: 0;
bottom: 0; }

h1, h2, h3, h4, h5, h6 {
margin: 20px 0 10px;
padding: 0;
font-weight: bold;
-webkit-font-smoothing: antialiased;
cursor: text;
position: relative; }

h1:hover a.anchor, h2:hover a.anchor, h3:hover a.anchor, h4:hover a.anchor, h5:hover a.anchor, h6:hover a.anchor {
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text-decoration: none; }

h1 tt, h1 code {
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h3 tt, h3 code {
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h4 tt, h4 code {
font-size: inherit; }

h5 tt, h5 code {
font-size: inherit; }

h6 tt, h6 code {
font-size: inherit; }

h1 {
font-size: 28px;
color: black; }

h2 {
font-size: 24px;
border-bottom: 1px solid #cccccc;
color: black; }

h3 {
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h4 {
font-size: 16px; }

h5 {
font-size: 14px; }

h6 {
color: #777777;
font-size: 14px; }

p, blockquote, ul, ol, dl, li, table, pre {
margin: 15px 0; }

hr {
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border: 0 none;
color: #cccccc;
height: 4px;
padding: 0;
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body > h2:first-child {
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padding-top: 0; }
body > h1:first-child {
margin-top: 0;
padding-top: 0; }
body > h1:first-child + h2 {
margin-top: 0;
padding-top: 0; }
body > h3:first-child, body > h4:first-child, body > h5:first-child, body > h6:first-child {
margin-top: 0;
padding-top: 0; }

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h1 p, h2 p, h3 p, h4 p, h5 p, h6 p {
margin-top: 0; }

li p.first {
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li {
margin: 0; }
ul, ol {
padding-left: 30px; }

ul :first-child, ol :first-child {
margin-top: 0; }

dl {
padding: 0; }
dl dt {
font-size: 14px;
font-weight: bold;
font-style: italic;
padding: 0;
margin: 15px 0 5px; }
dl dt:first-child {
padding: 0; }
dl dt > :first-child {
margin-top: 0; }
dl dt > :last-child {
margin-bottom: 0; }
dl dd {
margin: 0 0 15px;
padding: 0 15px; }
dl dd > :first-child {
margin-top: 0; }
dl dd > :last-child {
margin-bottom: 0; }

blockquote {
border-left: 4px solid #dddddd;
padding: 0 15px;
color: #777777; }
blockquote > :first-child {
margin-top: 0; }
blockquote > :last-child {
margin-bottom: 0; }

table {
padding: 0;border-collapse: collapse; }
table tr {
border-top: 1px solid #cccccc;
background-color: white;
margin: 0;
padding: 0; }
table tr:nth-child(2n) {
background-color: #f8f8f8; }
table tr th {
font-weight: bold;
border: 1px solid #cccccc;
margin: 0;
padding: 6px 13px; }
table tr td {
border: 1px solid #cccccc;
margin: 0;
padding: 6px 13px; }
table tr th :first-child, table tr td :first-child {
margin-top: 0; }
table tr th :last-child, table tr td :last-child {
margin-bottom: 0; }

img {
max-width: 100%; }

span.frame {
display: block;
overflow: hidden; }
span.frame > span {
border: 1px solid #dddddd;
display: block;
float: left;
overflow: hidden;
margin: 13px 0 0;
padding: 7px;
width: auto; }
span.frame span img {
display: block;
float: left; }
span.frame span span {
clear: both;
color: #333333;
display: block;
padding: 5px 0 0; }
span.align-center {
display: block;
overflow: hidden;
clear: both; }
span.align-center > span {
display: block;
overflow: hidden;
margin: 13px auto 0;
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pre {
background-color: #f8f8f8;
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font-size: 13px;
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background-color: transparent;
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sup {
font-size: 0.83em;
vertical-align: super;
line-height: 0;
}
* {
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}
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body {
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}
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table, pre {
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}
pre {
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}
}
-->

继承

本小节知识点:

  1. 继承基本概念
  2. OC中的继承关系
  3. OC中如何实现继承

1.继承基本概念

  • 现实生活中的继承 - 交通工具类是一个基类(也称做父类),通常情况下所有交通工具所共同具备的特性，如速度与额定载人的数量
  • 按照生活常规,我们来继续给交通工具来细分类的时候,我们会分别想到有汽车类和飞机类等,汽车类和飞机类同样具备速度和额定载人数量这样的特性,而这些特性是所有交通工具所共有的,那么就可以让汽车或飞机类继承交通工具类，这样当建立汽车类和飞机类的时候我们无需再定义交通工具类（基类）中已经有的成员和方法,而只需要??述汽车类和飞机类所特有的特性即可。
  • 飞机类和汽车类的特性是由在交通工具类原有特性基础上增加而来的,那么飞机类和汽车类就是交通工具类的派生类(也称做子类)。以此类推,层层递增, 这种子类获得父类特性的概念就是继承
  • 继承的重要性 

2.OC中的继承关系

  • B类继承A类，那么B类将拥有A类的所有属性和方法，此时我们说A类是B类的父类，B类是A类的子类
  • C类继承B类，那么C类将拥有B类中的所有属性和方法，包括B类从A类中继承过来的属性和方法，此时我们说B类是C类的父类，C类是B类的子类
  • 注意:
    • 基类的私有属性能被继承,不能在子类中访问。
    • OC中的继承是单继承:也就是说一个类只能一个父类,不能继承多个父类
    • 子类与父类的关系也称为isA（是一个）关系，我们说 子类isA父类，也就是子类是一个父类，比如狗类继承动物类，那么我们说狗isA动物，也就是狗是一个动物。在如汽车继承交通工具，那么们说汽车isA交工工具，也就是汽车是一个交通工具
    • 继承的合理性:引用《大话西游》里的一句话来描述继承的。“人是人他妈生的,妖是妖他妈生的!”

3.OC中如何实现继承

  • 在声明子类的时候，在子类名称后面通过：父类名称方式来实现继承
@interface 子类名称 : 父类名称

@end

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h1, h2, h3, h4, h5, h6 {
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h1 {
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继承相关特性

本小节知识点:

  1. 方法重写
  2. 继承中方法调用的顺序
  3. 继承的注意事项

1.方法重写

  • 在子类中实现与父类中同名的方法，称之为方法重写；
  • 重写以后当给子类发送这个消息的时候，执行的是在子类中重写的那个方法，而不是父类中的方法。
  • 如果想在子类中调用被子类重写的父类的方法，可以通过super关键字
  • 使用场景：当从父类继承的某个方法不适合子类,可以在子类中重写父类的这个方法。

2.继承中方法调用的顺序

  • 1、在自己类中找
  • 2、如果没有,去父类中找
  • 3、如果父类中没有,就去父类的父类中
  • 4、如果父类的父类也没有,就还往上找,直到找到基类(NSObject)
  • 5、如果NSObject都没有就报错了 >+ 如果找到了就执行这个方法，就不再往后查找了

3.继承的注意事项

  • 子类不能定义和父类同名的成员变量，私有成员变量也不可以；因为子类继承父类，子类将会拥有父类的所有成员变量，若在子类中定义父类同名成员变量 属于重复定义。
  • OC类支持单一继承,不支持多继承；也就是说一个类只能有一个直接父类
  • OC类支持多层继承 ,如下图所示

*:first-child {
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margin-left: -30px;
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position: absolute;
top: 0;
left: 0;
bottom: 0; }

h1, h2, h3, h4, h5, h6 {
margin: 20px 0 10px;
padding: 0;
font-weight: bold;
-webkit-font-smoothing: antialiased;
cursor: text;
position: relative; }

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font-size: inherit; }

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font-size: inherit; }

h1 {
font-size: 28px;
color: black; }

h2 {
font-size: 24px;
border-bottom: 1px solid #cccccc;
color: black; }

h3 {
font-size: 18px; }

h4 {
font-size: 16px; }

h5 {
font-size: 14px; }

h6 {
color: #777777;
font-size: 14px; }

p, blockquote, ul, ol, dl, li, table, pre {
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多态基本概念

本小节知识点:

  1. 【了解】什么是多态?
  2. 【掌握】多态的条件
  3. 【了解】多态的优点

1.什么是多态?

  • 什么是多态:多态就是某一类事物的多种形态

    • 猫: 猫-->动物
    • 狗: 狗-->动物
    • 男人 : 男人 -->人 -->高级动物
    • 女人 : 女人 -->人 -->高级动物
  • 程序中的多态:父类指针指向子类对象

2.多态的条件

  • 有继承关系
  • 子类重写父类方法
  • 父类指针指向子类对象 objc 狗 *g = [狗 new]; 动物 *a = [狗 new]; 猫 *c = [猫 new]; 动物 *a = [猫 new];

- 表现：当父类指针指向不同的对象的时候，通过父类指针调用被重写的方法的时候，会执行该指针所指向的那个对象的方法

3.多态的优点

  • 多态的主要好处就是简化了编程接口。它允许在类和类之间重用一些习惯性的命名,而不用为每一个新的方法命名一个新名字。这样,编程接口就是一些抽象的行为的集合,从而和实现接口的类的区分开来。

- 多态也使得代码可以分散在不同的对象中而不用试图在一个方法中考虑到所有可能的对象。 这样使得您的代码扩展性和复用性更好一些。当一个新的情景出现时,您无须对现有的代码进行 改动,而只需要增加一个新的类和新的同名方法。

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多态的实现

本小节知识点:

  1. 【掌握】如何实现多态
  2. 【了解】多态的原理

3. 【掌握】多态的注意点

1.如何实现多态

  • Animal是父类,子类有Cat 和 Dog,子类分别重写了父类中的eat方法;实例化对象的时候可以用下面的方法:
Animal *animal = nil;

//实例化猫的对象
animal = [Cat new];
[animal eat];

//实例化狗的对象
animal = [Dog new];
[animal eat];

2.多态的原理

  • 动态绑定:

    • 动态类型能使程序直到执行时才确定对象的真实类型
    • 动态类型绑定能使程序直到执行时才确定要对那个对象调用的方法
  • OC不同于传统程序设计语言,它可以在运行时加入新的数据类型和新的程序模块:动态类型识别,动态绑定,动态加载
  • id类型:通用对象指针类型,弱类型,编译时不进行具体类型检查

3.多态的注意点

  • 1)如果存在多态,父类是可以访问子类特有的方法
假设 子类 Dog 有一个特有的方法bark
[dog bark];
Animal *an2 = [Dog new];
[(Dog*)an2 bark]; //把父类的指针,强制类型转换
  • 2)如果不存在多态,父类是不可以访问子类特有的方法的
Animal *an3 = [Animal new];
[(Dog*)an3 bark]; //错误的,不能强制转换

OC基础(7)

时间： 2024-10-09 07:16:58

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