scrollViewDidEndScrollingAnimati

#pragma mark - 监听
/**
 *  点击了顶部的标题按钮
 */
- (void)titleClick:(XMGTitleButton *)titleButton
{
    // 修改按钮状态
    self.clickedTitleButton.selected = NO;
    titleButton.selected = YES;
    self.clickedTitleButton = titleButton;
     
    // 移除底部下划线
    [UIView animateWithDuration:0.25 animations:^{
        self.titleUnderlineView.width = titleButton.titleLabel.width;
        self.titleUnderlineView.centerX = titleButton.centerX;
    }];
     
    // 让scrollView滚动到对应的位置(不要去修改contentOffset的y值)
    CGPoint offset = self.scrollView.contentOffset;
    offset.x = titleButton.tag * self.scrollView.width;
    [self.scrollView setContentOffset:offset animated:YES];
   //不是人为拖拽scrollView导致滚动完毕，会调用scrollViewDidEndScrollingAnimation这个方法
}
 
#pragma mark - <UIScrollViewDelegate>
/**
 *  滚动完毕就会调用（如果不是人为拖拽scrollView导致滚动完毕，才会调用这个方法）
 */
- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView
{
    int index = scrollView.contentOffset.x / scrollView.width;
    UIViewController *willShowChildVc = self.childViewControllers[index];
     
    // 如果这个子控制器的view已经添加过了，就直接返回
    if (willShowChildVc.isViewLoaded) return;
     
    // 添加子控制器的view
    willShowChildVc.view.frame = scrollView.bounds;
    [scrollView addSubview:willShowChildVc.view];
}
 
/**
 *  滚动完毕就会调用（如果是人为拖拽scrollView导致滚动完毕，才会调用这个方法）
 */
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    int index = scrollView.contentOffset.x / scrollView.width;
    // 点击对应的按钮
    [self titleClick:self.titleButtons[index]];
     
    // 添加子控制器的view
    [self scrollViewDidEndScrollingAnimation:scrollView];
}