subView 的UIButton无法点击

Question

代码：

UIButton *mainButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
[mainButton setImage:[UIImage imageNamed:@"CircleShape.png"] forState:UIControlStateNormal];
mainButton.center = CGPointMake(self.view.frame.size.width/2.0f, self.view.frame.size.height/2.0f);
[self.view addSubview:mainButton];

UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(0, 100, 200, 100)];
[subView setBackgroundColor:[UIColor purpleColor]];
[mainButton addSubview:subView];

UIButton *secondButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
[secondButton setImage:[UIImage imageNamed:@"CircleShape.png"] forState:UIControlStateNormal];
secondButton.center = CGPointMake(subView.frame.size.width/2.0f, subView.frame.size.height/2.0f);
[subView addSubview:secondButton];

为什么mainButton 可以点击，但是secondButton就不可以点击呢。

Answer 1

在self.view添加子view。

UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(0, 100, 200, 100)];
[subView setBackgroundColor:[UIColor purpleColor]];
[self.view addSubview:subView];

UIButton *secondButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
[secondButton setImage:[UIImage imageNamed:@"CircleShape.png"] forState:UIControlStateNormal];
secondButton.center = CGPointMake(subView.frame.size.width/2.0f, subView.frame.size.height/2.0f);
[subView addSubview:secondButton];
UIButton *thirdButton = [[UIButton alloc] initWithFrame:CGRectMake(100, 0, 100, 100)];
[secondButton setImage:[UIImage imageNamed:@"CircleShape.png"] forState:UIControlStateNormal];
secondButton.center = CGPointMake(subView.frame.size.width/2.0f, subView.frame.size.height/2.0f);
[subView addSubview:secondButton];