UIButton设置为圆形按钮并增加边框

   UIButton *btn = [UIButton buttonWithType:UIButtonTypeSystem];
    btn.frame = CGRectMake(100, 100, 100, 100);
    
    // 设置按钮四个圆角的半径，默认为0，这里取边长一半便是一个圆
    btn.layer.cornerRadius = 50.0;
    // 设置边框的宽度
    btn.layer.borderWidth = 1.0;
    
    CGColorSpaceRef spaceRef = CGColorSpaceCreateDeviceRGB();
    CGColorRef colorRef = CGColorCreate(spaceRef, (CGFloat[]){255/255.0, 0/255.0, 0/255.0, 1});
    
    // 设置边框的颜色
    btn.layer.borderColor = colorRef;
    btn.backgroundColor = [UIColor lightGrayColor];
    [btn setTitle:@"Button" forState:UIControlStateNormal];