CAGradientLayer *gradientLayer = [CAGradientLayer layer];

    UIColor* colA = [UIColorcolorWithWhite:0alpha:0.2];

    UIColor* colB = [UIColorcolorWithWhite:0alpha:0];

    gradientLayer.colors=@[(__bridgeid)colA.CGColor, (__bridgeid)colB.CGColor,];

    gradientLayer.locations=@[@0,@1.0];

    gradientLayer.startPoint=CGPointMake(0,0);

    gradientLayer.endPoint=CGPointMake(0,1.0);

    gradientLayer.frame=CGRectMake(0,0,SCREEN_WIDTH,Ww(40));

    [self.im layeraddSublayer:gradientLayer];