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];
