NSNotificationCenter removeObserver不起作用

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");
    }

即使删除观察者后，我仍在登录SShot。

还有其他方法可以删除UIApplicationUserDidTakeScreenshotNotification观察者。

Answer 1

来自Apple Doc：

要注销观察结果，您传递返回的对象以此removeObserver的方法：您必须调用removeObserver：或removeObserver：name：object：由任何指定的对象之前addObserverForName：object：queue：usingBlock：被释放。

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

您正在尝试删除磨损的观察者，self在这里不是观察者，该观察者是add方法返回的对象

Answer 2

这是在Swift 4中的操作方法...

    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 3

哈里斯代码是正确的，除了一个小细节，现在对于Swift 4来说是这样

私人var观察者：任意！而不是私有var观察者：NSObjectProtocol！因此代码应为：

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 4

尝试使用此代码

至添加观察者

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(userDidTakeScreenshot) name:UIApplicationUserDidTakeScreenshotNotification object:nil];
}

- (void)userDidTakeScreenshot {
    // Screenshot taken, act accordingly.
}

和删除特定的观察者

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

至删除所有观察者

- (void)viewWillDisappear:(BOOL)animated {
        [super viewWillDisappear:animated];
        [[NSNotificationCenter defaultCenter] removeObserver:self];
    }

让我知道它是否对您有用！!!!