1.接口文件

1.1.方法

接口文件只向外部暴露了一个方法：

/**
 为一个指定的task绑定一个加载菊花控件
 */
- (void)setAnimatingWithStateOfTask:(nullable NSURLSessionTask *)task;

2.实现文件

2.1.AFActivityIndicatorViewNotificationObserver私有类

2.1.1.接口

2.1.1.1.属性

/**
 加载菊花控件
 */
@property (readonly, nonatomic, weak) UIActivityIndicatorView *activityIndicatorView;

2.1.1.2.方法

/**
 以指定的加载菊花控件初始化
 */
- (instancetype)initWithActivityIndicatorView:(UIActivityIndicatorView *)activityIndicatorView;

/**
 设置要绑定的task
 */
- (void)setAnimatingWithStateOfTask:(NSURLSessionTask *)task;

2.1.2.实现

接口方法

- (instancetype)initWithActivityIndicatorView:(UIActivityIndicatorView *)activityIndicatorView
{
    self = [super init];
    if (self) {
        // 保存传入的加载菊花控件
        _activityIndicatorView = activityIndicatorView;
    }
    return self;
}

- (void)setAnimatingWithStateOfTask:(NSURLSessionTask *)task {
    // 创建通知中心对象
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    
    // 先移除掉之前添加通知
    [notificationCenter removeObserver:self name:AFNetworkingTaskDidResumeNotification object:nil];
    [notificationCenter removeObserver:self name:AFNetworkingTaskDidSuspendNotification object:nil];
    [notificationCenter removeObserver:self name:AFNetworkingTaskDidCompleteNotification object:nil];
    
    // 如果传入的task不为nil
    if (task) {
        // 如果task的状态不是已经执行完成
        if (task.state != NSURLSessionTaskStateCompleted) {
            // 如果task的状态是运行中就显示加载菊花控件，否则就隐藏
            UIActivityIndicatorView *activityIndicatorView = self.activityIndicatorView;
            if (task.state == NSURLSessionTaskStateRunning) {
                [activityIndicatorView startAnimating];
            } else {
                [activityIndicatorView stopAnimating];
            }

            // 注册通知监听task的开始、完成和暂停
            [notificationCenter addObserver:self selector:@selector(af_startAnimating) name:AFNetworkingTaskDidResumeNotification object:task];
            [notificationCenter addObserver:self selector:@selector(af_stopAnimating) name:AFNetworkingTaskDidCompleteNotification object:task];
            [notificationCenter addObserver:self selector:@selector(af_stopAnimating) name:AFNetworkingTaskDidSuspendNotification object:task];
        }
    }
}

通知回调方法

- (void)af_startAnimating {
    // 如果接收到了task启动的通知，就在主队列异步回调中显示加载菊花控件
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.activityIndicatorView startAnimating];
    });
}

- (void)af_stopAnimating {
    // 如果接收到了task完成或暂停的通知，就在主队列异步回调中隐藏加载菊花控件
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.activityIndicatorView stopAnimating];
    });
}

声明周期方法

- (void)dealloc {
    // 移除掉添加通知
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    
    [notificationCenter removeObserver:self name:AFNetworkingTaskDidCompleteNotification object:nil];
    [notificationCenter removeObserver:self name:AFNetworkingTaskDidResumeNotification object:nil];
    [notificationCenter removeObserver:self name:AFNetworkingTaskDidSuspendNotification object:nil];
}

2.2.方法实现

- (AFActivityIndicatorViewNotificationObserver *)af_notificationObserver {
    // 通过运行时的关联对象为UIActivityIndicatorView添加了一个属性：af_notificationObserver，这个属性保存的就是上面看过的那个私有类
    AFActivityIndicatorViewNotificationObserver *notificationObserver = objc_getAssociatedObject(self, @selector(af_notificationObserver));
    if (notificationObserver == nil) {
        notificationObserver = [[AFActivityIndicatorViewNotificationObserver alloc] initWithActivityIndicatorView:self];
        objc_setAssociatedObject(self, @selector(af_notificationObserver), notificationObserver, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return notificationObserver;
}

- (void)setAnimatingWithStateOfTask:(NSURLSessionTask *)task {
    // 生成AFActivityIndicatorViewNotificationObserver对象，并通过关联对象保存在扩展的属性af_notificationObserver中，然后调用这个对象的绑定task的方法
    [[self af_notificationObserver] setAnimatingWithStateOfTask:task];
}