- (void)reloadData
{
    [_tableView reloadData];
    
    for (UIView *view in _tableView.subviews) {
        if ([view isKindOfClass:[UIControl class]]) {
            _indexControl = (UIControl *)view;
        }
    }
}

/// 點擊右側(cè)索引時的代理方法
- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
{
    _sectionLabel.text = title;  // 顯示 組號標題 的Label
    if (_sectionLabel.hidden) { // 隱藏了，顯示它
        _sectionLabel.hidden = NO;
    }
    
    // 延遲 1 秒隱藏
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
		//  isTracking: A Boolean value indicating whether the control is currently tracking touch events.
        if (!_indexControl.isTracking) { // 沒有觸摸時，隱藏它
            _sectionLabel.hidden = YES;
        }
    });
    
    return index;
}