带有NSNotification的removeObserver ......我做错了什么？

问题描述

基本上，我有一个view1，在某些时候，调用view2（通过 presentModalViewController：animated：）。当按下view2中的某个 UIButton 时，view2会在view1中调用通知方法，然后立即关闭。通知方法会弹出一个警告。

Basically, I have a view1 which at some point, calls view2 (via presentModalViewController:animated:). When a certain UIButton in view2 is pressed, view2 is calls a notification method in view1 and immediately afterward is dismissed. The notification method pops up an alert.

通知方法正常工作并被适当调用。问题是，每次创建view1时（一次只能存在一个view1），我可能会创建另一个 NSNotification ，因为如果我从view0（菜单）开始to view1，然后来回几次，我从通知方法中获得了一系列相同的警报消息，就像我打开一个view1一样多次。

The notification method works fine and is called appropriately. The problem is, every time view1 is created (only one view1 should exist at a time), I presumably get another NSNotification being created because if I go from view0 (the menu) to view1, then back and forth a few times, I get a series of the same alert message, one after another, from the notification method as many times as I opened a view1.

这是我的代码，请告诉我我做错了什么：

Here is my code, please tell me what I'm doing wrong:

View1.m

-(void) viewDidLoad {
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(showAlert:) 
                                                 name:@"alert" 
                                               object:nil];
}

-(void) showAlert:(NSNotification*)notification {
    // (I've also tried to swap the removeObserver method from dealloc
    // to here, but it still fails to remove the observer.)
    // < UIAlertView code to pop up a message here. >
}

-(void) dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [super dealloc];
}

View2.m

-(IBAction) buttonWasTapped {
    [[NSNotificationCenter defaultCenter] postNotificationName:@"alert" 
                                                        object:nil];
    [self dismissModalViewControllerAnimated:YES];
}

-(void) dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [super dealloc];
}

推荐答案

致电 -dealloc 不会自动发生 - 在视图控制器的生命周期中仍然可能存在一些生命。在该时间范围内，该视图控制器仍然订阅了该通知。

Calling -dealloc doesn't automatically happen after the view controller is dismissed — there can still be some "life" left in the view controller's lifetime. In that timeframe, that view controller is still subscribed for that notification.

如果您移除中的观察者-viewWillDisappear：或 -viewDidDisappear：，这将产生更直接的效果：

If you remove the observer in -viewWillDisappear: or -viewDidDisappear:, this will have a more immediate effect:

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

这篇关于带有NSNotification的removeObserver ......我做错了什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！