渐变色

- (void)setupDurationLabelBgView
{
    CGFloat bgimageViewWidth = 165 * kBigScreenViewWidthRate;
    CGFloat bgimageViewHeight = 20 * kBigScreenViewWidthRate;

    UIView *durationLabelBgView = [[UIView alloc] init];
    [_imgView addSubview:durationLabelBgView];
    [durationLabelBgView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.right.bottom.mas_equalTo(_imgView);
        make.height.mas_equalTo(bgimageViewHeight);
    }];
    UIColor *color1 = UIColorFromHexWithAlpha(0x000000, 0);
    UIColor *color2 = UIColorFromHexWithAlpha(0x000000, 1);
    CAGradientLayer *commonLayer = [self gradientLayerWithColor1:color1 color2:color2];
    commonLayer.frame = CGRectMake(0, 0, bgimageViewWidth, bgimageViewHeight);
    [durationLabelBgView.layer addSublayer:commonLayer];
}

- (CAGradientLayer *)gradientLayerWithColor1:(UIColor *)color1 color2:(UIColor *)color2{
    //初始化CAGradientlayer对象，使它的大小为UIView的大小
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    
    //设置渐变区域的起始和终止位置（范围为0-1）
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint = CGPointMake(1, 0);
    
    gradientLayer.colors = @[(__bridge id)color1.CGColor,
                             (__bridge id)color2.CGColor];
    //设置颜色分割点（范围：0-1）
    gradientLayer.locations = @[@(0.0f), @(0.6)];
    
    return gradientLayer;
}