NSNotificationCenter removeObserver无法正常工作

Question

-(void)viewDidAppear:(BOOL)animated {
            NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];
                [[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationUserDidTakeScreenshotNotification object:nil queue:mainQueue usingBlock:^(NSNotification *note) {
                    NSLog(@"SShot");
            }];
        }

- (void)viewWillDisappear:(BOOL)animated{
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationUserDidTakeScreenshotNotification object:nil];
    NSLog(@"VWD");
        }

 -(void)viewDidDisappear:(BOOL)animated {
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationUserDidTakeScreenshotNotification object:nil];
        NSLog(@"VDD");
    }

我SShot删除了观察者后,我正在登录控制台.

有没有其他方法可以删除UIApplicationUserDidTakeScreenshotNotification观察者.

Answer 1

以下是如何在Swift 4中完成的...

    private var observer: Any!

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        observer = NotificationCenter.default.addObserver(forName: NSNotification.Name("SomeNotification"), object: nil, queue: nil) { notification in
            //do something
        }
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        NotificationCenter.default.removeObserver(observer)
    }

Answer 2

来自Apple Doc:

要取消注册观察,请将此方法返回的对象传递给removeObserver:.你必须调用removeObserver:或removeObserver:名称:对象:对象:队列:usingBlock:由addObserverForName指定的任何对象之前被释放.

NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
[center removeObserver:self.localeChangeObserver];

你试图删除worng观察者,self这里不是观察者,观察者是add方法返回的对象