監聽當鍵盤將要出現時

OC版

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

監聽當鍵將要退出時

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

swift版

NotificationCenter.default.addObserver(self, selector: #selector(keyBoardShow(noty:)), name: Notification.Name.UIKeyboardWillShow, object: nil)
        
NotificationCenter.default.addObserver(self, selector: #selector(keyBoardHidden(noty:)), name: Notification.Name.UIKeyboardWillHide, object: nil)

OC版

當鍵盤出現

- (void)keyboardWillShow:(NSNotification *)notification
{
    //獲取鍵盤的高度
    NSDictionary *userInfo = [notification userInfo];
    NSValue *value = [userInfo objectForKey:UIKeyboardFrameBeginUserInfoKey];
    CGRect keyboardRect = [value CGRectValue];
    int height = keyboardRect.size.height;
}

當鍵退出

- (void)keyboardWillHide:(NSNotification *)notification
{
    //獲取鍵盤的高度
    NSDictionary *userInfo = [notification userInfo];
    NSValue *value = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
    CGRect keyboardRect = [value CGRectValue];
    int height = keyboardRect.size.height; 
} 

swift版

鍵盤彈出

@objc func keyBoardShow(noty: Notification) {
    guard let userInfo = noty.userInfo else {return}
    let value = userInfo["UIKeyboardFrameBeginUserInfoKey"] as! NSValue
    let keyboardRect = value.cgRectValue
    let keyboradHeight = keyboardRect.size.height
}

鍵盤退出

@objc func keyBoardShow(noty: Notification) {
    guard let userInfo = noty.userInfo else {return}
    let value = userInfo["UIKeyboardFrameEndUserInfoKey"] as! NSValue
    let keyboardRect = value.cgRectValue
    let keyboradHeight = keyboardRect.size.height
}