tableview（scrollview）被拉动后能立即滚动到顶端

再仔细说下：

1：tableview滑动前，下面悬浮的按钮隐藏
2：tableview被拉动后，下面悬浮的按钮出现，点击这个按钮tableview滚动到顶端。（便于分页加载多页后用户能立即滚动到顶端）

- (void)viewDidLoad

{
    aTopBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    aTopBtn.frame = CGRectMake(ScreenWidth-50,ScreenHeight-64-105, 35, 35);
    aTopBtn.backgroundColor = [UIColor clearColor];
    aTopBtn.hidden=YES;
    [aTopBtn setImage:[UIImage imageNamed:@"zs_shanghuabiao"] forState:UIControlStateNormal];
    [aTopBtn addTarget:self action:@selector(aToping:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:aTopBtn];
    
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView{

NSLog(@"scrollView.contentOffset.y%f",scrollView.contentOffset.y);
    if (scrollView.contentOffset.y>0) {
        aTopBtn.frame = CGRectMake(ScreenWidth-50,ScreenHeight-64-105, 35, 45);
        aTopBtn.hidden=NO;
        [aTopBtn setImage:[UIImage imageNamed:@"zs_huitou"] forState:UIControlStateNormal];

} else {
        aTopBtn.frame = CGRectMake(ScreenWidth-50,ScreenHeight-64-105, 35, 35);
        aTopBtn.hidden=YES;
        [aTopBtn setImage:[UIImage imageNamed:@"zs_shanghuabiao"] forState:UIControlStateNormal];
    }
}

//回到顶端

-(void)aToping:(UIButton *)sender{

[self.tableView scrollRectToVisible:CGRectMake(0, 0, 1, 1) animated:NO];

}