Objective c 如何将一个项目拖放到另一个项目上

我正在尝试创建一个小游戏，但在拖放对象时遇到了一个问题：我在两个按钮上使用UIPangestureRecognitor。我想让按钮2在按钮1和按钮2重叠时高亮显示。我假设它应该发生在UIgestureRecognitzerStateStart中，所以我这样写：

//This code to make button1 move
CGPoint translation = [recognizer translationInView:self.view];
recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x, 
                                     recognizer.view.center.y + translation.y);
[recognizer setTranslation:CGPointMake(0, 0) inView:self.view];

//This code to handle what happens when button 1 is dragged around
if (recognizer.state == UIGestureRecognizerStateBegan) {
    //And this code to handle what happens when button1 and button2 overlap
    if (CGRectContainsPoint([button2 frame], translation)) {
        button2.highlighted = YES;
    }
}

问题似乎来自if（CGRectContainsPoint（[button2 frame]，translation]）语句。有人能帮忙吗