文森說技術

// In a UIView subclass

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
{
    // 檢查自己
    if ([self checkInteractableWithView:self point:point event:event])
    {
        return YES;
    }

    // 檢查 subviews
    for (UIView *view in self.subviews) 
    {
        if ([self checkInteractableWithView:view point:point event:event])
        {
            return YES;
        }
    }

    return NO;
} 

- (BOOL)checkInteractableWithView:(UIView *)view point:(CGPoint)point event:(UIEvent *)event
{
    if ( ! view.hidden && 
        view.alpha > 0 && 
        view.userInteractionEnabled && 
        [view pointInside:[self convertPoint:point toView:view] withEvent:event])
    {
        return YES;
    }
    else
    {
        return NO;
    }
}