Obj-C - NSNotification 执行两次？

Question

由于某种原因，UIKeyboardWillHideNotification 在我下面的代码中被执行了两次——我不知道为什么。我知道这一点是因为我的 NSLog（“关闭！”）在我的控制台中出现了两次。我是否遗漏了一些明显的东西（不，我没有第二次将 UIKeyboardWillHideNotification 粘贴到我的代码中）。

-(void)viewDidLoad {

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillChange:) name:UIKeyboardWillShowNotification object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleKeyboard:) name:UIKeyboardWillHideNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleKeyboard:) name:UIKeyboardWillShowNotification object:nil];

}

- (void)handleKeyboard:(NSNotification*)aNotification{
    NSDictionary* info = [aNotification userInfo];
    NSValue* value = [info objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    NSTimeInterval duration = 3;
    [value getValue:&duration];

    if (aNotification.name == UIKeyboardWillShowNotification) {

        self.upView.frame = CGRectOffset(self.upView.frame, 0, -self.keyboardHeight); self.tableView.frame = CGRectOffset(self.tableView.frame, 0, -self.keyboardHeight);

        [self moveCustomView:YES duration:duration];
    }

    if (aNotification.name == UIKeyboardWillHideNotification) {
        /** KEYBOARD HIDE **/


        self.upView.frame = CGRectOffset(self.upView.frame, 0, self.keyboardHeight); self.tableView.frame = CGRectOffset(self.tableView.frame, 0, self.keyboardHeight);

        [self moveCustomView:NO duration:duration];
        NSLog(@"CLOSED!");
    }


}

Answer 1

确保删除 viewDidDisappear 中的观察者，因为某些原因可能不会重新分配视图控制器，并且 viewDidLoad 中的代码会在添加两次观察者时执行两次

// 目标c

 - (void)viewWillDisappear:(BOOL)paramAnimated{
   [super viewWillDisappear:paramAnimated];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter]  removeObserver:self name:UIKeyboardWillHideNotification object:nil];

}

// 斯威夫特

 override func viewDidDisappear(_ animated: Bool)
{


    NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIKeyboardDidShow, object: nil)

    NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIKeyboardWillHide, object: nil)


}

Answer 2

一定要从 dealloc 方法中移除观察者。如果你不删除它并且它的内存没有被释放，它会监听其他页面上的键盘行为。此外，您不应向同一个观察者添加两次相同的通知。

Answer 3

而不是使用相同的方法来隐藏和显示通知。您可以使用两种不同的方法。

[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWasShown:)
                                                 name:UIKeyboardDidShowNotification object:nil];

[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillBeHidden:)
                                                 name:UIKeyboardWillHideNotification object:nil];

现在，为了改变你的框架，你可以使用以下代码

NSDictionary* info = [aNotification userInfo];
   CGSize *kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
self.tableView.frame = CGRectOffset(self.tableView.frame, 0, -kbSize.height); 

Answer 4

请尝试一下：

我做了什么：

• 将订阅移至 viewWillAppear

• 在 vi​​ewWillDisappear 中添加了“取消订阅”

• 在dealloc 中添加了“取消订阅”（应该与您的问题无关，但这仍然是正确的做法）

• 在您的处理程序中将 == 替换为 isEqual（也很可能与您的问题无关）。

那里可能有一些错别字。对不起，如果是这样的话。

-(void)viewWillAppear {
    [super viewWillAppear];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillChange:) name:UIKeyboardWillShowNotification object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleKeyboard:) name:UIKeyboardWillHideNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleKeyboard:) name:UIKeyboardWillShowNotification object:nil];
}


-(void)viewDidLoad {
    [super viewDidLoad];
    //Leaving this method here just to point out that everything was moved to viewWillAppear
}

- (void)handleKeyboard:(NSNotification*)aNotification{
    NSDictionary* info = [aNotification userInfo];
    NSValue* value = [info objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    NSTimeInterval duration = 3;
    [value getValue:&duration];

    if ([aNotification.name isEqual: UIKeyboardWillShowNotification]) {
        self.upView.frame = CGRectOffset(self.upView.frame, 0, -self.keyboardHeight);
        self.tableView.frame = CGRectOffset(self.tableView.frame, 0, -self.keyboardHeight);
        [self moveCustomView:YES duration:duration];
    }

    if ([aNotification.name isEqual: UIKeyboardWillHideNotification]) {
        /** KEYBOARD HIDE **/
        self.upView.frame = CGRectOffset(self.upView.frame, 0, self.keyboardHeight); 
        self.tableView.frame = CGRectOffset(self.tableView.frame, 0, self.keyboardHeight);

        [self moveCustomView:NO duration:duration];
        NSLog(@"CLOSED!");
    }
}

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

-(void)viewWillDisappear {
    [super viewWillDisappear];
    [self unsubscribe];
}

-(void)dealloc {
    [self unsubscribe];
}