SCLAlertView Objective-C版本的问题

问题的描述：Bug with Keyboard on iPad in Landscape

我是在iPhone上发现这个问题的，在带有TextField的SCLAlertView显示时，点击TextField弹出键盘后，SCLAlertView并不会向上移动，而取消键盘后，SCLAlertView向下移动。

这样就会导致用户输入被键盘覆盖的问题，用户体验不是很好。

原因：
SCLAlerView.m中，注册监听了KeyBoard的事件：

- (void)addObservers
{
    if(_canAddObservers)
    {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
        _canAddObservers = NO;
    }
}

我们来看看keyboardWillShow，keyboardWillHide分别做了什么事情：

- (void)keyboardWillShow:(NSNotification *)notification
{
    if(_keyboardIsVisible) return;
    
    [UIView animateWithDuration:0.2f animations:^{
        CGRect f = self.view.frame;
        f.origin.y -= KEYBOARD_HEIGHT + PREDICTION_BAR_HEIGHT;
        self.view.frame = f;
    }];
    _keyboardIsVisible = YES;
}

- (void)keyboardWillHide:(NSNotification *)notification
{
    if(!_keyboardIsVisible) return;
    
    [UIView animateWithDuration:0.2f animations:^{
        CGRect f = self.view.frame;
        f.origin.y += KEYBOARD_HEIGHT + PREDICTION_BAR_HEIGHT;
        self.view.frame = f;
    }];
    _keyboardIsVisible = NO;
}

看上去非常正确，如果键盘出现，就调整y坐标的位置，上移SCLAlertView，键盘消失，就取消之前调整的位置。

但奇怪的就是，有时候，keyboardWillShow调用完成之后，系统调用了viewWillLayoutSubviews方法，而这里面又初始化SCLAlertView的位置居中：

    // Set new main frame
    CGRect r;
    if (self.view.superview != nil) {
        // View is showing, position at center of screen
        r = CGRectMake((sz.width-_windowWidth)/2, (sz.height-_windowHeight)/2, _windowWidth, _windowHeight);
    } else {
        // View is not visible, position outside screen bounds
        r = CGRectMake((sz.width-_windowWidth)/2, -_windowHeight, _windowWidth, _windowHeight);
    }
    
    self.view.frame = r;

这导致之前为了上移而调整的y坐标变回了句中，而keyboardWillHide调用之后，却没有触发viewWillLayoutSubviews，因此导致键盘消失后，SCLAlertView的位置下调。

既然不能阻止viewWillLayoutSubviews的调用，只能在他里面做下控制。修改：

    // Set new main frame
    CGRect r;
    if (self.view.superview != nil) {
        // View is showing, position at center of screen
        r = CGRectMake((sz.width-_windowWidth)/2, (sz.height-_windowHeight)/2, _windowWidth, _windowHeight);
    } else {
        // View is not visible, position outside screen bounds
        r = CGRectMake((sz.width-_windowWidth)/2, -_windowHeight, _windowWidth, _windowHeight);
    }
    
    if (_keyboardIsVisible) {
        r.origin.y -= KEYBOARD_HEIGHT + PREDICTION_BAR_HEIGHT;
    }
    
    self.view.frame = r;