设置渐变效果

CAGradientLayer *_gradientLayer;
UIView *_layerView;

    _layerView = [[UIView alloc] initWithFrame:CGRectMake(0,  self.iconImageView.height - SetHeight(30), self.iconImageView.width,  SetHeight(30))];

    _gradientLayer = [CAGradientLayer layer];  // 设置渐变效果
    _gradientLayer.bounds = _layerView.bounds;
    _gradientLayer.borderWidth = 0;

    _gradientLayer.frame = _layerView.bounds;
    _gradientLayer.colors = [NSArray arrayWithObjects:
                             (id)[[UIColor clearColor] CGColor],
                             (id)[[UIColor blackColor] CGColor],nil];
    _gradientLayer.startPoint = CGPointMake(0.2, 0.2);
    _gradientLayer.endPoint = CGPointMake(0.2, 1.0);

    [_layerView.layer insertSublayer:_gradientLayer atIndex:0];
    [self.iconImageView addSubview:_layerView];

    [_layerView addSubview:self.AcountNumLabel];