实现渐变色通常会用图片代替，本文利用CAGradientLayer类绘制渐变色

// 创建view

   UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 100, [UIScreen mainScreen].bounds.size.width, 200)];
   view.layer.cornerRadius = 10;
   view.layer.masksToBounds = YES;
   [self.view addSubview:view];
   
   //初始化CAGradientlayer对象，使它的大小为UIView的大小

   CAGradientLayer *gradientLayer = [CAGradientLayer layer];
   gradientLayer.frame = view.bounds;

   //将CAGradientlayer对象添加在我们要设置背景色的视图的layer层
   [view.layer addSublayer:gradientLayer];
   
   //设置渐变区域的起始和终止位置（范围为0-1）startPoint & endPoint设置为(0,0)(1.0,0)代表水平方向渐变,(0,0)(0,1.0)代表竖直方向渐变
   gradientLayer.startPoint = CGPointMake(0, 0);
   gradientLayer.endPoint = CGPointMake(1, 0);

   //设置颜色数组
   gradientLayer.colors = @[(__bridge id)[UIColor blueColor].CGColor,
                            (__bridge id)[UIColor redColor].CGColor];

   //设置颜色分割点（范围：0-1）
   gradientLayer.locations =  @[@(0.0f), @(1.0f)];

屏幕快照 2017-12-21 下午4.44.48.png