关于iPhone中按钮背景图片的问题

我在iphone应用里添加了两个按钮，每个按钮都有背景图片。我想让用户点击button2的时候显示在其中的button1中的图片。用了很多方法也没实现，请各位大侠帮帮忙。谢谢！

代码如下：

 btn1 = [UIButton buttonWithType:UIButtonTypeCustom];
[btn1 setImage:[UIImage imageNamed:@"4.png"] forState:UIControlStateNormal];
btn1.frame=CGRectMake(61, 60, 50, 50);
[btn1 addTarget:self action:@selector(Button1Method) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:btn1];  

btn2 = [UIButton buttonWithType:UIButtonTypeCustom];
[btn2 setImage:[UIImage imageNamed:@"8.png"] forState:UIControlStateNormal];
btn2.frame=CGRectMake(112, 60, 50, 50);
[btn2 addTarget:self action:@selector(Button2Method) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:btn2]; 



-(void)Button2Method
{

 [btn2 setImage:[UIImage imageNamed:btn1.currentBackgroundImage] forState:UIControlStateNormal];

}