颜色透明渐变效果

    CAGradientLayer *colorLayer = [CAGradientLayer layer];
    colorLayer.frame = CGRectMake(0, 0, gradientView.frame.size.width, gradientView.frame.size.height);
    [gradientView.layer addSublayer:colorLayer];
    
    //添加渐变的颜色组合
    colorLayer.colors = [NSArray arrayWithObjects:
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.0] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.1] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.2] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.3] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.4] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.5] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.6] CGColor],
                         (id)[[[UIColor clearColor] colorWithAlphaComponent:.7] CGColor],
                        nil];

参考链接:
UIView 的渐变色呈现
CAGradientLayer的一些属性解析