实现这个渐变导航条的功能，需要拿到前后两个button，所以在创建button的时候要把它们加入到一个可变的数组中。

// 滚动中调用
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat offsetX = scrollView.contentOffset.x;
// 取出左右两个button的index
    NSInteger leftIndex = offsetX / ZHJScreenW;
    NSInteger rightIndex = leftIndex + 1;
// 取出左边的button
    UIButton *leftButton = self.buttons[leftIndex];
    
// 取出右边的button，考虑到在最右边的时候不用再滑动了，所以要判断下
    UIButton *rightButton = nil;
    if (rightIndex < self.buttons.count) {
        rightButton = self.buttons[rightIndex];
    }
 // 取出左边的缩放值
    CGFloat scaleR = offsetX / ZHJScreenW - leftIndex;
 // 取出右边的缩放值 
    CGFloat scaleL = 1 - scaleR;
    
 // maxTitleScale ＝ 1.3 是最大缩放大小
    CGFloat transScale = maxTitleScale - 1;
    leftButton.transform = CGAffineTransformMakeScale(scaleL * transScale + 1, scaleL * transScale + 1);
    
    rightButton.transform = CGAffineTransformMakeScale(scaleR * transScale + 1, scaleR * transScale + 1);
    
  // 用rgb来实现颜色的渐变
    UIColor *rightColor = [UIColor colorWithRed:scaleR green:scaleR blue:scaleR alpha:1];
    UIColor *leftColor = [UIColor colorWithRed:scaleL green:scaleL blue:scaleL alpha:1];
    
    [leftButton setTitleColor:leftColor forState:UIControlStateNormal];
    [rightButton setTitleColor:rightColor forState:UIControlStateNormal];
    
    // 设置指示器的位置
    // 算出button的宽度
    CGFloat buttonW = (self.view.width - 100) / 3.0;
    //  设置动画
    self.indicator.transform = CGAffineTransformMakeTranslation(buttonW * (offsetX / ZHJScreenW), 0);
    
}