Question

I have a UITableView in my MainViewController. When a user taps a cell,

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

selectedRow = indexPath;

....

[self performSegueWithIdentifier:@"OtherViewControllerSegue" sender:self];
}

and they are taken to another UIViewController (let’s call it OtherViewController). In OtherViewController, the name for the selected cell is set. When OtherViewController is dismissed, it updates the cell in MainViewController with the new name:

[[[mainvc.myTableView cellForRowAtIndexPath:mainvc.selectedRow] textLabel] setText:namecell.textField.text];
    [self.navigationController popViewControllerAnimated:YES];

This all works fine until I have more cells than will fit on the screen. If there are more cells than will fit on the screen (8 for iPhone or 16 for iPad), then this will also set the name for every eighth or sixteenth cell respectively. Any ideas on what I am doing wrong?

Update:

- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [pointsTableView dequeueReusableCellWithIdentifier:@"myTableCell"];
return cell;
}

Answer 1

This is due to cell-reuse and you are mixing up your model with your view (in the MVC context).

A table-cell is a transient thing, once it goes off the screen it is reused (instead of creating new cells) when another cell is needed. This is what the dequeueReusableCellWithIdentifier: method does.

This means you can’t store data in there and expect it to still be valid later on. In this example you are trying to store the name in the table cell. The reason to set a property (like the label text) on any view object is purely for display, not for storage. So to solve this problem you should maintain a list of objects in your model (this could be in separate classes or in an array in your mainvc object for example). Then in cellForRowAtIndexPath: you should set the label text every time – even when there should be no label you need to set it to nil or an empty string because the cells are re-used it might contain something from the last time it was used.

Update:
Instead of calling cellForRowAtIndexPath: yourself and setting its text, you should set the text in your model using a method or property in your controller and then tell the table view to reload that cell. The code might look something like this:

// This code is in where you want to set the text from
[mainvc setText:someText forIndexPath:indexPath];

.. and in your main view controller:

- (void)setText(NSString*)newText forIndexPath:(NSIndexPath*)indexPath
{
    // Store the text in your model here...
    ...

    // If the view is loaded, the table view should reload the cell.
    if(self.isViewLoaded)
    {
        [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }
}

The table view will then call cellForRowAtIndexPath: where the text will be set correctly. This may seem a little convoluted at first, but when you get used to using the Model-View-Controller design pattern you will find that keeping the jobs of each MVC component separate like this will mean your code is tidier, easier to understand, has less bugs, is easier to update/extend, etc.