How to keep UITableView contentoffset after calling -reloadData

Question

CGPoint offset = [_table contentOffset];
[_table reloadData];
[_table setContentOffset:offset animated:NO];    //unuseful

//    __block UITableView *tableBlock = _t         


        

Answer 1

Swift 4 variant of @Skywalker answer:

fileprivate var heightDictionary: [IndexPath: CGFloat] = [:]

override func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    heightDictionary[indexPath] = cell.frame.size.height
}

override func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    let height = heightDictionary[indexPath]
    return height ?? UITableViewAutomaticDimension
}

---

Another solution (fetched from MessageKit):

This method should be called instead of reloadData. This can fit for specific cases.

public func reloadDataAndKeepOffset() {
    // stop scrolling
    setContentOffset(contentOffset, animated: false)
        
    // calculate the offset and reloadData
    let beforeContentSize = contentSize
    reloadData()
    layoutIfNeeded()
    let afterContentSize = contentSize
        
    // reset the contentOffset after data is updated
    let newOffset = CGPoint(
        x: contentOffset.x + (afterContentSize.width - beforeContentSize.width),
        y: contentOffset.y + (afterContentSize.height - beforeContentSize.height))
    setContentOffset(newOffset, animated: false)
}

Answer 2

By default, reloadData keeps the contentOffset. However, it could be updated if you do have inaccurate estimatedRowHeight values.

Answer 3

I was having trouble with this because I mess with cell sizing in my cellForRowAtIndexPath method. I noticed that the sizing information was off after doing reloadData, so I realized I needed to force it to layout immediately before setting the content offset back.

CGPoint offset = tableView.contentOffset;
[tableView.messageTable reloadData];
[tableView layoutIfNeeded]; // Force layout so things are updated before resetting the contentOffset.
[tableView setContentOffset:offset];

Answer 4

If you implement estimatedHeightForRowAtIndexPath method and your estimate is not right, you will possible get into this situation.

To solve this, you can return a large height that bigger than every cell height in your tableView, like this:

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath { 
    return 800.f; // if 800 is bigger than every possible value of your cell height.
}

Answer 5

For it works fine

[tView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]
             atScrollPosition:UITableViewScrollPositionTop
                     animated:NO];

Answer 6

This is working 100%

change the tableView.reloadData() 

into

tableView.reloadRows(at: tableView!.indexPathsForVisibleRows!, with: .none)