为什么我的NSNotification会多次调用它的观察者？ [英] Why is my NSNotification its observer called multiple times?

问题描述

在App中我使用了几个viewcontrollers。在一个viewcontroller上，一个观察者初始化如下：

Within an App I make use of several viewcontrollers. On one viewcontroller an observer is initialized as follows:

[[NSNotificationCenter defaultCenter] removeObserver:self name:@"MyNotification" object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(myMethod:) name:@"MyNotification" object:nil];

即使在初始化之前删除 NSNotification 也是如此 myMethod：的执行次数通过相应viewcontroller上的重复视图量来总结。

Even when removing the NSNotification before initializing the number of executions of myMethod: is being summed up by the amount of repeated views on the respective viewcontroller.

为什么这是否会发生？如何避免myMethod：被调用一次以上。

Why does this happen and how can I avoid myMethod: being called more then once.

注意：我确保使用断点，我多次调用postNotification时没有犯错。

Note: I made sure by using breakpoints that I did not made mistakes on calling postNotification multiple times.

编辑：这就是我的postNotification的样子

This is how my postNotification looks like

NSArray * objects = [NSArray arrayWithObjects:[NSNumber numberWithInt:number],someText, nil];
NSArray * keys = [NSArray arrayWithObjects:@"Number",@"Text", nil];
NSDictionary * userInfo = [NSDictionary dictionaryWithObjects:objects forKeys:keys];
[[NSNotificationCenter defaultCenter] postNotificationName:@"myNotification" object:self userInfo:userInfo];

编辑：即使在我订阅了viewwillappear之后：我得到了相同的结果。 myMethod：被多次调用。 （我重新加载viewcontroller的次数）。

edit: even after moving my subscribing to viewwillappear: I get the same result. myMethod: is called multiple times. (number of times i reload the viewcontroller).

-(void)viewWillAppear:(BOOL)animated {

    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"MyNotification" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(myMethod:) name:@"MyNotification" object:nil];
}

编辑：我的生命周期似乎有些问题。 ViewDidUnload和dealloc没有被调用，但是viewdiddisappear被调用。

edit: something seems wrong with my lifecycle. ViewDidUnload and dealloc are not getting called, however viewdiddisappear is getting called.

我将Viewcontroller推送到堆栈的方式如下，其中parent是tableview子类（点击时）此视图控制器启动的行：

The way I push my Viewcontroller to the stack is as follows where parent is a tableview subclass (on clicking the row this viewcontroller is initiated:

detailScreen * screen = [[detailScreen alloc] initWithContentID:ID andFullContentArray:fullContentIndex andParent:parent];
[self.navigationController pushViewController:screen animated:YES];

解决方案：

移除nsnotification到viewdiddisappear就行了。感谢指导！

Moving removal of nsnotification to viewdiddisappear did the trick. Thanks for guidance!

推荐答案

根据这个描述，一个可能的原因是你的viewcontrollers被过度保留而且你认为它们没有被释放。如果事情被过度保留，这种情况很常见。所以，你认为你只有一个一个给定的viewcontroller活动的实例，而你实际上有几个l ive实例，他们都听取通知。

Based on this description, a likely cause is that your viewcontrollers are over-retained and not released when you think they are. This is quite common even with ARC if things are over-retained. So, you think that you have only one instance of a given viewcontroller active, whereas you actually have several live instances, and they all listen to the notifications.

如果我遇到这种情况，我会在viewcontroller的dealloc方法中放置一个断点并确保它被正确释放，如果这是您的应用程序的预期设计。

If I was in this situation, I would put a breakpoint in the viewcontroller’s dealloc method and make sure it is deallocated correctly, if that’s the intended design of your app.

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