NSNotificationCenter 可能会导致错误。你知道更优雅的解决方案吗？

发布于 2025-01-06 10:59:59 字数 741 浏览 4 评论 0原文

我可以将观察者两次（意外地）添加到通知中心，并且我将收到两次通知。是否可以只收到一份通知？你知道更优雅的解决方案吗？

我向您展示这个示例是因为这可能会导致错误。

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

- (void)keyboardDidShow:(NSNotification *)ntf
{
}

原文

I can add observer twice (by accident) to the notification center and I will get notifications twice.
Is it possible to get only one notification? Do you know more elegant solutions?

I show you this example because this may lead to bugs.

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

- (void)keyboardDidShow:(NSNotification *)ntf
{
}

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夏九 2025-01-13 11:00:00

如果您不确定是否在其他地方添加了观察者，则可以在每次添加观察者时使用以下代码，

[[NSNotificationCenter defaultCenter] removeObserver:self name:aName object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:aSelector name:aName object:nil];

这样您就可以删除旧的观察者（如果存在）并添加新的观察者。

这不是 100% 的失败证明，但它是一个开始。在调用异步或其他特殊情况的多线程应用程序中，这可能会失败。

If you're not sure if you added the observer somewhere else, you can use the following code everytime you're adding an Observer

[[NSNotificationCenter defaultCenter] removeObserver:self name:aName object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:aSelector name:aName object:nil];

This way you are removing the old one (if it existed) and adding a new one.

It's not 100% fail proof but it's a start. This could fail in Multi-Threaded apps where the calls are being made async or other unique situations.

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