Remembering scroll position on UITableView

问题:

I have a bit of a problem with my iOS app in xcode. I have a UITableView that loads a few hundred cells. When I scroll down to a specific cell and drill down to detailedviewcontrollers and return again the master view table has returned all the way to the top. I've had a look at the following 2 questions that are similar.

How can I get the UITableView scroll position so I can save it?

Setting scroll position in UITableView

I still can't get these to work. I'm not the most experienced coder so I'm really struggling with this.

I know things like viewWillDisappear and viewDidAppear need to be changed, but I just really can't get much further than that.

On this table I have a reloadData feature so it is possible to pull down the latest data from the server and also a working search bar.

Anyway, a helping hand would be great. Thanks,

Luke

回答1:

See here you have to first save the scrolled position of tableView i.e. contentOffset of tableView and then reuse it when you are coming back to tableView.

1)When and where you will save it :

When : At the point, when you are drilling down to detailViewController save the contentOffset of tableView

How : float verticalContentOffset = tableView.contentOffset.y;

2) How will you set tableView back to the same scrolled position :

[tableView setContentOffset:CGPointMake(0, verticalContentOffset)];

Hope this will help you.

回答2:

Sorted!

With a bit of inspiration from Desdenova, whilst at work I had a good think about it and realised what it could be. Remembering that I had a search bar, I had implemented the following code a few months ago to hide it:

[self.tableView setContentOffset:CGPointMake(0,-20) animated:NO];

In naivety I put that in viewDidAppear rather than viewDidLoad. Obviously, this did hide the search bar, but with it being in the wrong void command it did it every time the masterDetailView returned to the top of the stack. So, after moving the above code to viewDidLoad it now still hides it, but only the once.

I'm just spelling it out like this for other beginners, like myself, who may come across the same problem and may just save their sanity!

Thanks to you all for your ideas that helped me out.

+1 to you all!

回答3:

If anyone is wondering, I tried the solution by Prashant N and it worked. However reloadData don't actually reset the scroll position anymore now, so I didn't have to do anything other than reloadData.

回答4:

My solution to this problem consisted in scrolling the table to the indexrow of the last item.

private func scrollToItem(item:Int, section:Int bottom:Bool = true, animated:Bool = false) {
    let indexPath = NSIndexPath(forRow: item:Int-1, inSection: section)
    var position = UITableViewScrollPosition.Bottom
    if (!bottom) { position = UITableViewScrollPosition.Top }
    self.tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: position, animated: animated)
}

回答5:

For some reason this was halfway working for me (sometimes the position would only be approximate). I finally used the following a priori less clean solution

NSIndexPath *firstVisibleIndexPath = [[self.tableView indexPathsForVisibleRows] objectAtIndex:0];
[self.tableView scrollToRowAtIndexPath:self.firstVisibleIndexPath atScrollPosition:UITableViewScrollPositionTop animated:NO];
self.firstVisibleIndexPath = firstVisibleIndexPath;

which worked better.

回答6:

My decision for a collection:

CGFloat oldCollectionViewHeight = self.messageCollectionView.contentSize.height;

[self.messageCollectionView reloadData];
[self.messageCollectionView layoutIfNeeded];

CGFloat newCollectionViewHeight = self.messageCollectionView.contentSize.height;

if (oldCollectionViewHeight) {
    self.messageCollectionView.contentOffset = CGPointMake(0, newCollectionViewHeight - oldCollectionViewHeight);
}

For the table, the principle is the same.

回答7:

As mentioned in other comments, scrolling to the top on Back navigation in a UINavigationController is not the default behavior.

Another cause might be that you are setting a cell near the top of the table as first responder in viewWillAppear, e.g. a search box or edit field near the top of your table. UITableViewController will scroll a first responder into view automatically, which is nice. As long as that's what you're trying to do. :) Take care to not set first responder in viewWillAppear unless that's what you want. Cheers, AZ

回答8:

You don’t need to do anything, while you are in the same view controller, your position will be the same. I’m afraid that somewhere in your view controller is being called a reloadData. Search for some method calling scrollToRowAtIndexPath.