How to overlay a transparent window on the system keyboard

AppDelegate.h

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) IBOutlet UIWindow *window;
@property ( strong ) IBOutlet UITextField * textField ;
@end

AppDelegate.m

@interface MyWindow : UIWindow
@end

@implementation MyWindow

-(UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
	return nil ;
}

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
	[[ NSNotificationCenter defaultCenter ] addObserver:self selector:@selector( keyboardWillShow: ) name:UIKeyboardWillShowNotification object:nil ] ;
	[[ NSNotificationCenter defaultCenter ] addObserver:self selector:@selector( keyboardDidHide: ) name:UIKeyboardDidHideNotification object:nil ] ;

	UITapGestureRecognizer * g = [[ UITapGestureRecognizer alloc ] initWithTarget:self action:@selector( backgroundViewTapped ) ] ;
	[ self.window.rootViewController.view addGestureRecognizer:g ] ;
	
    return YES;
}

static MyWindow * __keyboardCoverWindow = nil ;
-(void)keyboardWillShow:(NSNotification*)note
{
	CGRect keyboardFrame = [ [ note.userInfo valueForKey:UIKeyboardFrameEndUserInfoKey ] CGRectValue ] ;
	if ( !__keyboardCoverWindow )
	{
		__keyboardCoverWindow = [[ MyWindow alloc ] initWithFrame:keyboardFrame ] ;
	}
	
	__keyboardCoverWindow.backgroundColor = [[ UIColor redColor ] colorWithAlphaComponent:0.5f ] ;
	__keyboardCoverWindow.hidden = NO ;
	__keyboardCoverWindow.windowLevel = 100.0f ;
}

-(void)keyboardDidHide:(NSNotification*)note
{
	__keyboardCoverWindow.hidden = YES ;
}

-(void)backgroundViewTapped
{
	[ self.textField resignFirstResponder ] ;
}

@end