颜色渐变

在view的layer上添加一个渐变的layer

    CAGradientLayer *layer = [CAGradientLayer new];
    //colors存放渐变的颜色的数组
    layer.colors=@[(__bridge id)[UIColor redColor].CGColor,(__bridge id)[UIColor whiteColor].CGColor];
    /*** 起点和终点表示的坐标系位置，(0,0)表示左上角，(1,1)表示右下角     */
    layer.startPoint = CGPointMake(0.4, 0.4);
    layer.endPoint = CGPointMake(0.4, 0.41);
    layer.frame = self.bounds;
    self.color_layer = layer;
    [self.layer addSublayer:self.color_layer];

渐变过程加一个动画

    CABasicAnimation *gradient = [CABasicAnimation animationWithKeyPath:@"locations"];
    gradient.duration = 4.0;
//    gradient.fillMode = kCAFillModeForwards;
    gradient.fromValue = @[@(0),@(0)];
    gradient.toValue = @[@(0.2),@(1)];
    gradient.removedOnCompletion = NO;
    gradient.repeatCount = 1;
    [self.color_layer addAnimation:gradient forKey:nil];