UIButton，UIView添加渐变边框

思路参考
举例UIButtom思路：
1、 首先创建一个临时的 UIView
2、 然后利用 CAGradientLayer 在 UIView 上面进行渐变绘制
3、将UIView 进行截图返回 UIImage
4、将返回的 UIImage 设置到 UIButton 的 setBackgroundImage
这样就可以完成了一个UIButton 的渐变色 绘制，并且可以根据不用的颜色来设置Button UIControlStateNormal | UIControlStateHighlighted | UIControlStateDisabled 来进行设置效果。
5、在已经绘制好有渐变色的UIView 上面盖多一个白色的 UIView 比 上面那个UIView 小一些像素 即可
下面直接贴代码

/**
 btnRect:按钮的frame
 borderWidth:按钮的边框宽度
 默认圆角为高度的1/2，修改圆角需要修改gradientLayer和whiteView的cornerRadius
 */
- (UIImage *)getImageWithFrame:(CGRect)btnRect withBorderWidth:(CGFloat)borderWidth{
    CGFloat btnWidth = btnRect.size.width;
    CGFloat btnHeight = btnRect.size.height;
    //用来放置渐变色的view
    UIView *crView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, btnWidth, btnHeight)];
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.colors = @[(__bridge id)[UIColor colorWithRed:1 green:172/255.0 blue:64/255.0 alpha:1].CGColor, (__bridge id)[UIColor colorWithRed:254/255.0 green:119/255.0 blue:119/255.0 alpha:1].CGColor];
    gradientLayer.locations = @[@0.3, @0.7];
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint = CGPointMake(1.0, 0);
    gradientLayer.frame = CGRectMake(0, 0, crView.frame.size.width, crView.frame.size.height);
    gradientLayer.cornerRadius = btnHeight*1.0/2;
    [crView.layer addSublayer:gradientLayer];
    //空白view
    UIView *whiteView = [[UIView alloc] initWithFrame:CGRectMake(borderWidth, borderWidth, btnWidth-borderWidth*2, btnHeight-borderWidth*2)];
    whiteView.layer.cornerRadius = btnHeight*1.0/2;
    whiteView.backgroundColor = [UIColor whiteColor];
    [crView addSubview:whiteView];
    //把配置好的view转变成image
    CGSize s = CGSizeMake(btnWidth, btnHeight);
    // 下面方法，第一个参数表示区域大小。第二个参数表示是否是非透明的。如果需要显示半透明效果，需要传NO，否则传YES。第三个参数就是屏幕密度了
    UIGraphicsBeginImageContextWithOptions(s, NO, [UIScreen mainScreen].scale);
    [crView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage*image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
    
}

使用方法：

    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame = CGRectMake(0, 200, 200, 50);
    [btn setTitle:@"+关注" forState:UIControlStateNormal];
    [btn setBackgroundImage:[self getImageWithFrame:btn.frame withBorderWidth:0.5] forState:UIControlStateNormal];
    [self.view addSubview:btn];

参考文档还写了渐变文字的方法，我尝试了下没成功，改天再看