三种方法都是通过touchesBegin监听屏幕的触摸实现
一、performSelector方式
1 #import "ViewController.h"
2 @interface ViewController ()
3 @property (weak, nonatomic) IBOutlet UIImageView *imageView;
4 @end
5 @implementation ViewController
6 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
7 {
8 //放入子线程
9 [self performSelectorInBackground:@selector(download3) withObject:nil];
10 }
11
12 //下载放入子线程，显示图片应该放在主线程！！！否则会导致刷新问题
13 - (void)download3
14 {
15 //图片的网络路径
16 NSURL *url = [NSURL URLWithString:@"http://ww2.sinaimg.cn/mw690/63e6fd01jw1f3f3rf75goj20qo0zkagy.jpg"];
17 //下载图片数据
18 NSData *data = [NSData dataWithContentsOfURL:url];
19
20 //生成图片
21 UIImage *image = [UIImage imageWithData:data];
22 //回到主线程显示图片方法一：
23 // [self performSelectorOnMainThread:@selector(showImage:) withObject:image waitUntilDone:YES];
24 //回到主线程显示图片方法二：
25 //waitUntilDone:表示是否等待主线程做完事情后往下走，YES表示做完后执行下面事，NO表示跟下面事一起执行
26 [self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];
27 //回到主线程显示图片方法三：
28 [self.imageView performSelector:@selector(setImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:YES];
29 }
30 //主线程显示图片
31 - (void)showImage:(UIImage *)image
32 {
33 self.imageView.image = image;
34 }
二、GCD方式
1 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
2 {
3 dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
4 //图片的网络途径
5 NSURL *url = [NSURL URLWithString:@"http://ww2.sinaimg.cn/mw1024/75614297jw1f34e5llyz4j20qo0zj0zl.jpg"];
6 //加载图片
7 NSData *data = [NSData dataWithContentsOfURL:url];
8 //生成图片
9 UIImage *image = [UIImage imageWithData:data];\
10 //回到主线程
11 dispatch_async(dispatch_get_main_queue(), ^{
12 self.imageView.image = image;
13 });
14 });
15
16 }
三、operation方式(此种方式更具有面向对象特性！)
1 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
2 {
3 //直接开始子线程执行任务
4 [[[NSOperationQueue alloc] init] addOperationWithBlock:^{
5 NSURL *url = [NSURL URLWithString:@"http://ww4.sinaimg.cn/mw690/63e6fd01jw1ezxz499hy5j21gt0z94qq.jpg"];
6 NSData *data = [NSData dataWithContentsOfURL:url];
7 UIImage *image = [UIImage imageWithData:data];
8 //回到主线程
9 [[NSOperationQueue mainQueue] addOperationWithBlock:^{
10 //显示图片
11 self.imageView.image = image;
12 }];
13 }];
14 }
以上三种方式都需要在main storyboard中拖一个imageView，然后设置自动布！！