NSNotificationCenter removeObserver 不工作

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");
    }

即使我删除了观察者，我仍然 SShot 登录控制台。

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

Answer 1

来自Apple Doc：

To unregister observations, you pass the object returned by this method to removeObserver:. You must invoke removeObserver: or removeObserver:name:object: before any object specified by addObserverForName:object:queue:usingBlock: is deallocated.

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

你移除错误的观察者，self不是这里的观察者，观察者是add方法返回的对象

Answer 2

尝试使用此代码

到添加观察者

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

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

然后删除一个特定的观察者

- (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!!!!

Answer 3

这是 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 4

Harris 代码是正确的，除了 Swift 4 的小细节现在是

private var 观察者：任何！而不是私有变量观察者：NSObjectProtocol！所以代码应该是：

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)
}

NSNotificationCenter removeObserver 不工作

NSNotificationCenter removeObserver not working

objective-c

nsnotificationcenter

ios