创建线程方式-NSThread

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---

NSThread

（1）NSThread的基本使用

//第一种创建线程的方式：alloc init.
//特点：需要手动开启线程，可以拿到线程对象进行详细设置
    //创建线程
    /*
     第一个参数：目标对象
     第二个参数：选择器，线程启动要调用哪个方法
     第三个参数：前面方法要接收的参数（最多只能接收一个参数，没有则传nil）
     */
    NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(run:) object:@"daquan"];
     //启动线程
    [thread start];

//第二种创建线程的方式：分离出一条子线程
//特点：自动启动线程，无法对线程进行更详细的设置
    /*
     第一个参数：线程启动调用的方法
     第二个参数：目标对象
     第三个参数：传递给调用方法的参数
     */
    [NSThread detachNewThreadSelector:@selector(run:) toTarget:self withObject:@"我是分离出来的子线程"];

//第三种创建线程的方式：后台线程
//特点：自动启动线程，无法进行更详细设置
[self performSelectorInBackground:@selector(run:) withObject:@"我是后台线程"];

（2）设置线程的属性

   //设置线程的属性
    //设置线程的名称
    thread.name = @"线程A";

    //设置线程的优先级,注意线程优先级的取值范围为0.0~1.0之间，1.0表示线程的优先级最高,如果不设置该值，那么理想状态下默认为0.5
    thread.threadPriority = 1.0;

（3）线程的状态

//线程的各种状态：新建-就绪-运行-阻塞-死亡
//常用的控制线程状态的方法
[NSThread exit];//退出当前线程
[NSThread sleepForTimeInterval:2.0];//阻塞线程
[NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:2.0]];//阻塞线程
//注意：线程死了不能复生,即不能再使用该线程.

（4）线程安全

    01 前提：多个线程访问同一块资源会发生数据安全问题

    02 解决方案：加互斥锁

    03 相关代码：@synchronized(锁对象){//需要锁定的代码}

    04 专业术语-线程同步
    05 原子和非原子属性（是否对setter方法加锁）

（5）线程间通信

-(void)touchesBegan:(nonnull NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event
{
//    [self download2];

    //开启一条子线程来下载图片
    [NSThread detachNewThreadSelector:@selector(downloadImage) toTarget:self withObject:nil];
}

-(void)downloadImage
{
    //1.确定要下载网络图片的url地址，一个url唯一对应着网络上的一个资源
    NSURL *url = [NSURL URLWithString:@"http://p6.qhimg.com/t01d2954e2799c461ab.jpg"];

    //2.根据url地址下载图片数据到本地（二进制数据)
    NSData *data = [NSData dataWithContentsOfURL:url];

    //3.把下载到本地的二进制数据转换成图片
    UIImage *image = [UIImage imageWithData:data];

    //4.回到主线程刷新UI
    //4.1 第一种方式
//    [self performSelectorOnMainThread:@selector(showImage:) withObject:image waitUntilDone:YES];

    //4.2 第二种方式(直接调用系统的setImage:方法)
//    [self.imageViw performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];

    //4.3 第三种方式(可以选择任意线程)
    [self.imageView performSelector:@selector(setImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:YES];
}

（6）如何计算代码段的执行时间

//第一种方法
    NSDate *start = [NSDate date];
    //2.根据url地址下载图片数据到本地（二进制数据）
    NSData *data = [NSData dataWithContentsOfURL:url];

    NSDate *end = [NSDate date];
    NSLog(@"第二步操作花费的时间为%f",[end timeIntervalSinceDate:start]);

//第二种方法
    CFTimeInterval start = CFAbsoluteTimeGetCurrent();
    NSData *data = [NSData dataWithContentsOfURL:url];

    CFTimeInterval end = CFAbsoluteTimeGetCurrent();
    NSLog(@"第二步操作花费的时间为%f",end - start);