NSNotificationCenter 一篇文章导致观察者被调用两次

NSNotificationCenter是iOS开发中一种常用的观察者模式，它允许对象在特定事件发生时相互通信。然而，在使用NSNotificationCenter时，有时会出现观察者被调用两次的情况，这可能会导致一些意外的问题。本文将探讨这个问题，并提供一些解决方案。

objc
- (void)viewDidLoad {
    [super viewDidLoad];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(handleNotification:)
                                                 name:@"MyNotification"
                                               object:nil];
}
- (void)handleNotification:(NSNotification *)notification {
    NSLog(@"Notification received");
    // 其他处理逻辑
}
- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

objc
- (void)viewDidLoad {
    [super viewDidLoad];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(handleNotification:)
                                                 name:@"MyNotification"
                                               object:nil];
}
- (void)handleNotification:(NSNotification *)notification {
    NSLog(@"Notification received");
    // 其他处理逻辑
}
- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

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