ios把按钮切成圆形

//    把按钮弄成圆形方案：让btn的宽高相等，然后
//    btn.layer.cornerRdius = width/2.0;
//    btn.layer.maskToBounds = width/2.0；
CGRect rect = CGRectMake(40, 40, 80, 80);
UIButton * btn = [[UIButton alloc]initWithFrame:rect];
btn.backgroundColor = [UIColor colorWithRed:88.0/255.0 green:88.0/255.0 blue:88.0/255.0 alpha:0.3];
btn.layer.cornerRadius = 40.0;//（该值到一定的程度，就为圆形了。）
[btn  setBackgroundImage:[UIImage imageNamed:@"car"]  forState:UIControlStateNormal];
btn.layer.borderWidth = 1.0;

btn.layer.borderColor =[UIColor clearColor].CGColor;

btn.clipsToBounds = TRUE;//去除边界
[self.view addSubview:btn];