iOS - 获取系统键盘所在View

做自定义键盘可能需要用到这个，也有用更高级别的Window盖住键盘，这个在键盘view上用自定义键盘盖住原键盘，但是记得不需要的时候就把自定义键盘移除，否则在哪都是自定义键盘

代码是从Stack Overflow找到的，好用

- (UIView *)keyboardView
{
    UIWindow* tempWindow;

    //Because we cant get access to the UIKeyboard throught the SDK we will just use UIView.
    //UIKeyboard is a subclass of UIView anyways
    UIView* keyboard;

    NSLog(@"windows %ld", [[[UIApplication sharedApplication]windows]count]);

    //Check each window in our application
    for(int c = 0; c < [[[UIApplication sharedApplication] windows] count]; c ++)
    {
        //Get a reference of the current window
        tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:c];

        //Get a reference of the current view
        for(int i = 0; i < [tempWindow.subviews count]; i++)
        {
            keyboard = [tempWindow.subviews objectAtIndex:i];
            NSLog(@"view: %@, on index: %d, class: %@", [keyboard description], i, [[tempWindow.subviews objectAtIndex:i] class]);
            if([[keyboard description] hasPrefix:@"(lessThen)UIKeyboard"] == YES)
            {
                //If we get to this point, then our UIView "keyboard" is referencing our keyboard.
                return keyboard;
            }
        }

        for(UIView* potentialKeyboard in tempWindow.subviews)
            // if the real keyboard-view is found, remember it.
            if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) {
                if([[potentialKeyboard description] hasPrefix:@"] == YES)
                    keyboard = potentialKeyboard;
            }
            else if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 3.2) {
                if([[potentialKeyboard description] hasPrefix:@"] == YES)
                    keyboard = potentialKeyboard;
            }
            else {
                if([[potentialKeyboard description] hasPrefix:@"] == YES)
                    keyboard = potentialKeyboard;
            }
    }

    return keyboard;
}