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1. 用session：

- (void)setImageAction:(id)sender {    self.imV.image = [UIImage imageWithData:sender];}- (IBAction)image:(id)sender {    // 设置url    NSURL *url = [NSURL URLWithString:@"http://v.juhe.cn/movie/picurl?2583078"];    // 请求对象    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];    NSURLSession *session = [NSURLSession sharedSession];    // 建立连接 请求数据    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {        NSLog(@"%@", data);        // 给imV赋值                // 这样赋值 会等好久 图片才会刷出来 这个是多线程里的子线程，        self.imV.image = [UIImage imageWithData:data];        // 所有UI的刷新必须在主线程操作        // 将加载图片放到主线程        [self performSelectorOnMainThread:@selector(setImageAction:) withObject:data waitUntilDone:YES];    }];    [task resume];}

2. imageDownLoader：

#pragma mark  使用imageDownLoader下载图片- (IBAction)imageDownloader:(id)sender {    ImageDownloader *imageDl = [[ImageDownloader alloc] initWithImageUrl:@"http://v.juhe.cn/movie/picurl?2583078" delegate:self];    [imageDl startDownload];}- (void)imageDownloader:(ImageDownloader *)downloader didFinishedLoading:(UIImage *)downloadImage {    self.imV.image = downloadImage;}

3. KVO：

键值观察者：Key-Value-Observer

-(void)dealloc {    // 一定要移除观察者  移除 移除 移除    [self removeObserver:self forKeyPath:@"name"];    [self removeObserver:self forKeyPath:@"per.age"];}- (void)viewDidLoad {    [super viewDidLoad];    // 添加观察者    [self addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:@"shit"];            [self addObserver:self forKeyPath:@"per.age" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];}-(void)touchesBegan:(NSSet
   
     *)touches withEvent:(UIEvent *)event {    self.name = @"haha";    self.per = [[Person alloc] init];    self.per.age = @"hehe da";}-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary
    
      *)change context:(void *)context {//    NSLog(@" keyPath = %@   obj = %@   change = %@   con = %@", keyPath, object, change, context);        if ([keyPath isEqualToString:@"name"]) {        self.view.backgroundColor = [UIColor redColor];    }else        self.view.backgroundColor = [UIColor blueColor];    }
    
   

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