多线程（二）NSThread

一、NSThread优缺点

优点：NSThread是最轻量级的

缺点：需要自己管理线程的生命周期，线程同步。线程同步对数据的加锁会有一定的系统开销

二、NSThread的使用

• 创建线程：

+ (void)detachNewThreadSelector:(SEL)selector toTarget:(id)target withObject:(nullableid)argument;

- (instancetype)initWithTarget:(id)target selector:(SEL)selector object:(nullableid)argument; //argument:传输给target的唯一参数，也可以是nil

1. 直接创建线程，并开始执行线程

[NSThread detachNewThreadSelector:@selector(doSomething:) toTarget:self withObject:nil];

1. 先创建线程对象，然后再运行线程操作，在运行线程操作前可以设置线程的优先级等线程信息

NSThread* myThread = [[NSThread alloc] initWithTarget:self

selector:@selector(doSomething:)

object:nil];

[myThread start];

1. 不显式创建线程的方法，Swift中去掉了这个方法，苹果认为 performSelector: 不安全，，，，，

      NSObject *obj;

[obj performSelectorInBackground:@selector(doSomething) withObject:nil];

例子：

- (void)viewDidLoad {

[super viewDidLoad];

//    [NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL];
    NSURL *url = [NSURL URLWithString:@"http://h.hiphotos.baidu.com/image/pic/item/5366d0160924ab1828b7c95336fae6cd7b890b34.jpg"];
    NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(downloadImage:) object:url];
    [thread start];
}

- (void)downloadImage:(NSString *)url {
    NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
    UIImage *image = [[UIImage alloc]initWithData:data];
    if(image == nil){
       
    }else{
        [self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
    }
}

- (void)updateUI:(UIImage *)image {
    self.iconView.image = image;

}

1. 更新其他线程

- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array

- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait

1. 常用属性

//取消线程
    - (void)cancel;
    //启动线程
    - (void)start;
    //判断某个线程的状态的属性
    @property (readonly, getter=isExecuting) BOOL executing;
    @property (readonly, getter=isFinished) BOOL finished;
    @property (readonly, getter=isCancelled) BOOL cancelled;
    //设置和获取线程名字
    -(void)setName:(NSString *)n;
    -(NSString *)name;
    //获取当前线程信息
    + (NSThread *)currentThread;
    //获取主线程信息
    + (NSThread *)mainThread;
    //使当前线程暂停一段时间，或者暂停到某个时刻
    + (void)sleepForTimeInterval:(NSTimeInterval)time;

+ (void)sleepUntilDate:(NSDate *)date;