tableView中的奇怪错误

Question

I have a UITableView, I can add and delete cell to this table. I also have two buttons. 1 button adds "1" to the cell's text, Which is 1 so basically it counts when pressing the + button and subs when pressing the - button. My problem is with the very last cell. If i add 5 cells, its the 5th cell that has the problem. If i add 200 cells its the 200th cell, etc. The problem is when i press the - button, all the other cells keep turning blue when pressed, and this button stops turning blue. It stays white when i press it when the cells text is 0. I want it to keep turning blue like all the other cells when pressed. Here is my code:

- (IBAction)subtractLabelText:(id)sender
{
    cell = (UITableViewCell*)[sender superview];    

    if ( [[cell.textLabel text] intValue] == 0){ 
        [newBtn setEnabled:NO];
    }
    else{
        cell.textLabel.text = [NSString stringWithFormat:@"%d",[cell.textLabel.text    
        intValue] -1];
        [newBtn setEnabled:YES];
    }
}

This method is hooked up to the sub "-" button. Also, when i press the button when the text is = 0, the button is there but when i press it, it selects the cell and the table cell turns blue as if i selected that! Please help! Thanks everybody!

cellForRow:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:     
(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault 
        reuseIdentifier:CellIdentifier];
    } 
    cell.imageView.image = [imageArray objectAtIndex:indexPath.row];    
    cell.textLabel.text = [cells objectAtIndex:indexPath.row];

    newBtn = [[UIButton alloc]init];
    newBtn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    [newBtn setFrame:CGRectMake(260,20,55,35)];
    [newBtn addTarget:self action:@selector(subtractLabelText:) 
        forControlEvents:UIControlEventTouchUpInside];
    [newBtn setTitle:@"-" forState:UIControlStateNormal];
    [newBtn setEnabled:YES];
    [cell addSubview:newBtn];

    subBtn = [[UIButton alloc]init];
    subBtn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    [subBtn setFrame:CGRectMake(200,20,55,35)];
    [subBtn addTarget:self action:@selector(addLabelText:) 
        forControlEvents:UIControlEventTouchUpInside];
    [subBtn setTitle:@"+" forState:UIControlStateNormal];
    [subBtn setEnabled:YES];
    [cell addSubview:subBtn];
    return cell;
}

Answer 1

At a guess, I'd say it has to do with how the UITableViewCell s are being reused, in that the UI doesn't 'know' about the subview buttons on those cells.

Try commenting out the code in -cellForRowAtIndexPath that dequeues the reusable cells (so in effect you're always creating a new UITableViewCell regardless of whether cell==nil or not).

Edit: You're referencing newBtn in -subtractLabelText , but this is an ivar that doesn't necessarily refer to the button that sent the message. Try [sender setEnabled:NO] instead.

Answer 2

Based on your cellForRowAtIndexPath method, you are creating and adding new buttons to each cell regardless of whether they are being reused or 'brand new'.

Your code is doing something like this:

1. Check if there is a cell to be dequeued/reused
2. If yes, grab a reference to it. If no, create a new one.
3. Add buttons XYZ to the cell (your mistake is here)
4. Return the cell for the tableview to use

Imagine that in step 2, if you a reusing an existing cell, this cell already has the buttons XYZ added to it so you are essentially adding two extra button to it when you didn't need to.

You should move the code that sets up the cell buttons to inside the if (cell == nil) loop so the buttons are only created and added to the content view if you are initialising a new cell object.

Also make sure you look at the additional comments below which are not directly related to your question but may be relevant nonetheless.

==================================================================

[EDIT - ANSWER ABOVE, BUT THIS IS ALSO RELEVANT SO I LEFT IT HERE]

This will not solve your problem, but you should be adding your buttons to the cell's contentview instead of directly to the cell, ie:

[cell.contentView addSubView:buttonABC];

Once that's done, you will need to call superview twice to get the cell reference in your subtract/add method:

cell = (UITableViewCell*)[[sender superview] superview];    

From Apple's documentation on UITableViewCell

The content view of a UITableViewCell object is the default superview for content displayed by the cell. If you want to customize cells by simply adding additional views, you should add them to the content view so they will be positioned appropriately as the cell transitions into and out of editing mode.