悬浮按钮回顶部

    // 添加回到顶部按钮
    _topBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    _topBtn.frame = CGRectMake(self.view.frame.size.width-60, self.view.frame.size.height-100, 40, 40);
    [_topBtn setBackgroundImage:[UIImage imageNamed:@"nearby_return_top_btn"] forState:UIControlStateNormal];
    [_topBtn addTarget:self action:@selector(backToTopButton) forControlEvents:UIControlEventTouchUpInside];
    _topBtn.clipsToBounds = YES;
    _topBtn.hidden = YES;
    [self.view addSubview:_topBtn];

// MARK:  计算偏移量
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    //MARK:列表滑动偏移量计算
    CGPoint point = [self.tableView contentOffset];
    
    if (point.y >= 50) {
        self.topBtn.hidden = NO;
        [self.view bringSubviewToFront:self.topBtn];
    } else {
        self.topBtn.hidden = YES;
    }
}

//MARK: 点击移动到顶部
- (void)backToTopButton{
    [self.tableView setContentOffset:CGPointMake(0, 0) animated:YES];
}