UIView *bgView = [[UIView alloc] initWithFrame:CGRectMake(0, 60, SCREEN_WIDTH, 175-60)];
[_headerView addSubview:bgView];
//渐变效果
_gradientLayer = [CAGradientLayer layer]; // 设置渐变效果
_gradientLayer.bounds = self.view.bounds;
_gradientLayer.borderWidth = 0;
_gradientLayer.frame = self.view.bounds;
_gradientLayer.colors = [NSArray arrayWithObjects:
(id)[[UIColor clearColor] CGColor],
(id)[[UIColor colorWithRed:0 green:0 blue:0 alpha:0.5] CGColor], nil,nil];
_gradientLayer.startPoint = CGPointMake(0.5, 0.5);
_gradientLayer.endPoint = CGPointMake(0.5, 1.0);
[bgView.layer insertSublayer:_gradientLayer atIndex:0];