让UIImageView点击是现实高亮图，放手时现实默认图！
方法如下：
- (void)touchesBegan:(NSSet *) touches withEvent:(UIEvent *) event
{
_bubbleBg.highlighted = YES;
CarmenLog(@"touchesBegan");
}
- (void)touchesMoved:(NSSet *) touches withEvent:(UIEvent *) event
{
CarmenLog(@"touchesMoved");
}
- (void)touchesEnded:(NSSet *) touches withEvent:(UIEvent *) event
{
CarmenLog(@"touchesEnded");
}
- (void)touchesCancelled:(NSSet *) touches withEvent:(UIEvent *) event
{
_bubbleBg.highlighted = NO;
CarmenLog(@"touchesCancelled");
}
