iOS--多线程之线程间通讯

// waitUntilDone的含义:
//    如果传入的是YES: 那么会等到主线程中的方法执行完毕, 才会继续执行下面其他行的代码
//    如果传入的是NO: 那么不用等到主线程中的方法执行完毕, 就可以继续执行下面其他行的低吗

/*
 *  回到主线程执行，执行self的showImage方法，参数是image
 */
[self performSelectorOnMainThread:@selector(showImage:) withObject:image waitUntilDone:YES];

/*
 *  回到xx线程执行aSelector方法，参数是arg
 */
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait;

- (void)viewDidLoad
{
    // 1.给定图片的url
    NSURL *url = [NSURL URLWithString:@"http://b.hiphotos.baidu.com/image/pic/item/e4dde71190ef76c666af095f9e16fdfaaf516741.jpg"];
    // 2.开启线程，在后台执行download方法
   [self performSelectorInBackground:@selector(download:) withObject:url];
}

- (void)download:(NSURL *)url
{
    // 在子线程下载图片
    NSData *data = [NSData dataWithContentsOfURL:url];
    UIImage *image = [UIImage imageWithData:data];

    // 设置图片，执行self.imageView的setImage:方法
//    [self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];

    // 另一张设置图片的方法
    // 回到主线程中执行 showImage:方法，在此方法中设置图片
    [self performSelector:@selector(showImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:YES];

}

-(void)showImage:(UIImage *)image
{
    // 更新UI
    self.imageView.image = image;
}

    //获得当前时间，double型
    CFAbsoluteTime begin = CFAbsoluteTimeGetCurrent();

    // 获得当前时间
    NSDate *begin = [NSDate date];
    // 执行一些操作之后的时间
    NSDate *end = [NSDate date];
    // 时差
    NSLog(@"花费了多少秒 %f", [end timeIntervalSinceDate:begin]);

 dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    // 1.下载图片(耗时)
    dispatch_async(queue, ^{
        NSLog(@"%@", [NSThread currentThread]);
        // 1.创建URL
        NSURL *url = [NSURL  URLWithString:@"http://stimgcn1.s-msn.com/msnportal/ent/2015/08/04/7a59dbe7-3c18-4fae-bb56-305dab5e6951.jpg"];
        // 2.通过NSData下载图片
        NSData *data = [NSData dataWithContentsOfURL:url];
        // 3.将NSData转换为图片
        UIImage *image = [UIImage imageWithData:data];

        // 4.更新UI
//        self.imageView.image = image;
//        NSLog(@"更新UI完毕");
        // 如果是通过异步函数调用, 那么会先执行完所有的代码, 再更新UI
        // 如果是同步函数调用, 那么会先更新UI, 再执行其它代码
        dispatch_sync(dispatch_get_main_queue(), ^{
            NSLog(@"%@", [NSThread currentThread]);
            self.imageView.image = image;
            NSLog(@"更新UI完毕");
        });
        NSLog(@"Other");
    });

// 1.创建一个新的队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];

    // 2.添加任务(操作)
    [queue addOperationWithBlock:^{
        // 2.1在子线程中下载图片
        NSURL *url  = [NSURL URLWithString:@"http://imgcache.mysodao.com/img2/M04/8C/74/CgAPDk9dyjvS1AanAAJPpRypnFA573_700x0x1.JPG"];
        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *image = [UIImage imageWithData:data];

        // 2.2回到主线程更新UI
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            self.imageView.image = image;
        }];
    }];

/ 1.创建一个队列
    // 一般情况下, 在做企业开发时候, 都会定义一个全局的自定义队列, 便于使用
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];

    // 2.添加一个操作下载第一张图片
    __block UIImage *image1 = nil;
    NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
        NSURL *url  = [NSURL URLWithString:@"http://imgcache.mysodao.com/img2/M04/8C/74/CgAPDk9dyjvS1AanAAJPpRypnFA573_700x0x1.JPG"];
        NSData *data = [NSData dataWithContentsOfURL:url];
        image1 = [UIImage imageWithData:data];
    }];

    // 3.添加一个操作下载第二张图片
    __block UIImage *image2 = nil;
     NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
        NSURL *url  = [NSURL URLWithString:@"http://imgcache.mysodao.com/img1/M02/EE/B5/CgAPDE-kEtqjE8CWAAg9m-Zz4qo025-22365300.JPG"];
        NSData *data = [NSData dataWithContentsOfURL:url];
        image2 = [UIImage imageWithData:data];
    }];
    // 4.添加一个操作合成图片
    NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
        UIGraphicsBeginImageContext(CGSizeMake(200, 200));
        [image1 drawInRect:CGRectMake(0, 0, 100, 200)];
        [image2 drawInRect:CGRectMake(100, 0, 100, 200)];
        UIImage *res = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        // 5.回到主线程更新UI
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            self.imageView.image = res;
        }];
    }];

    // 6.添加依赖

    [op3 addDependency:op1];
    [op3 addDependency:op2];

    // 7.添加操作到队列中
    [queue addOperation:op1];
    [queue addOperation:op2];
    [queue addOperation:op3];