将图像设置成圆形
//将图形设置成圆形
//初始化并设label frame
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
//设置四角的半径 cornerRadius
label.layer.cornerRadius = label.frame.size.width / 2;
//剪切多余边界
label.clipsToBounds = YES;
//设置圆边界圆形的宽
label.layer.borderWidth = 3.0f;
//设置背景颜色
label.backgroundColor = [UIColor redColor];
//添加到父视图
[self.view addSubview:label];