关于键盘出现与隐藏时调整UITextField的显示位置问题

1、首先在ViewDidLoad里面添加注册键盘隐藏与出现的通知：

    ///< 注册通知，以便在键盘将要出现时，调整页面
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(onKeyboardWillShow:)
                                                 name:UIKeyboardWillShowNotification
                                               object:nil];
    ///< 注册通知，以便在键盘将要隐藏时，恢复页面
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(onKeyboardWillHide:)
                                                 name:UIKeyboardWillHideNotification
                                               object:nil];

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    
    /// 注意：在此处需要移除通知，否则容易照成崩溃
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];
    return;
}

#pragma mark - UIKeyboardWillShowNotification 通知
- (void)onKeyboardWillShow:(NSNotification *)notification {
    CGRect frame = self.view.frame;
    if (frame.origin.y < 0) {
        return;
    }
    // 获取键盘的高度
    CGFloat keyboardHeight = [self keyboardHeightWithKeyboardNotification:notification];
    frame.origin.y -= (keyboardHeight - 20);
    [UIView animateWithDuration:0.35 animations:^{
        self.view.frame = frame;
    }];
    return;
}

#pragma mark - UIKeyboardWillHideNotification 通知
- (void)onKeyboardWillHide:(NSNotification *)notification {
    CGRect frame = self.view.frame;
    if (frame.origin.y > 0) {
        return;
    }
    // 获取键盘的高度
    CGFloat keyboardHeight = [self keyboardHeightWithKeyboardNotification:notification];
    frame.origin.y += (keyboardHeight - 20);
    [UIView animateWithDuration:0.35 animations:^{
        self.view.frame = frame;
    }];
    return;
}

/// 获取键盘高度
- (CGFloat)keyboardHeightWithKeyboardNotification:(NSNotification *)notification {
    NSDictionary *info = notification.userInfo;
    NSValue *value = [info objectForKey:UIKeyboardFrameBeginUserInfoKey];
    CGSize keyboardSize = [value CGRectValue].size;
    CGFloat keyboardHeight = keyboardSize.height;
    
    return keyboardHeight;
}