UIButton颜色渐变 titleLabel字体不显示

CAGradientLayer *gradientLayer0 = [[CAGradientLayer alloc] init];
        gradientLayer0.frame = btn.bounds;
 //  创建渐变色数组，需要转换为CGColor颜色
        gradientLayer0.colors = @[
                                  (id)[UIColor colorWithRed:251.0f/255.0f green:151.0f/255.0f blue:8.0f/255.0f alpha:1.0f].CGColor,
                                  (id)[UIColor colorWithRed:255.0f/255.0f green:217.0f/255.0f blue:8.0f/255.0f alpha:1.0f].CGColor];
    //  设置颜色变化点，取值范围 0.0~1.0
        gradientLayer0.locations = @[@0, @1];
   //  设置渐变颜色方向，左上点为(0,0), 右下点为(1,1)
        [gradientLayer0 setStartPoint:CGPointMake(0, 1)];
        [gradientLayer0 setEndPoint:CGPointMake(1, 1)];
        [btn.layer insertSublayer:gradientLayer0 atIndex:0];//注意

   [btn.layer insertSublayer:gradientLayer0 atIndex:0];