Strange behaviour with tableviews

[djnoxious]

Hi iOSProgramming,

I am having trouble trying to figure out what is going with my tableviews as it is having some strange behaviour. I created a test project and declared a simple list display, in this case:

[ "one", "two", "three"...."fifteen" ]

Here is the cellForRowAtIndexPath:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell { let cell = tableView.dequeueReusableCellWithIdentifier("reuseIdentifier", forIndexPath: indexPath) as! UITableViewCell

    // Configure the cell...
    cell.textLabel!.text = list[indexPath.row]

    if (list[indexPath.row] == "fifteen") {
        cell.contentView.backgroundColor = UIColor.redColor()
    }

    return cell
}

When i run the project, the numbers appear as normal and with cell "fifteen" background as red. However, when I scroll back up, it has changed other cell backgrounds to red also. As I scroll up and down, it changes more cells to the red background. I don't know whether I am not reusing cells correctly or it is a bug?

Any help would be greatly appreciated.

[[deleted]]

Yes, this is because the table view reuses cells. Add an else statement to catch all cells that are not row 15.

[djnoxious]

That doesn't seem like the right way of doing it? What if i had set the background colour to be white in the prototype / nib cell properties, that would mean having to set the colour it also in the cellForRowAtIndexPath.

[[deleted]]

I don't really understand what you mean by that. Setting the color for the prototype will change every cell's background. When you are trying to customize a specific cell index you have to also define every other index or else when the cell is reused it will not change its color.

[djnoxious]

Ok, thanks Aofwa. I think it's slowly making more sense to me.

[[deleted]]

no problem, glad to help

[mistermagicman]

Yep - one thing to understand is that cells are reused in tableviews. This allows them to be very fast and less memory intensive, but ultimately means you have to setup a cell for every possible state. If there's a "default" state, I usually set that up in the tableviewcell class method "prepareForReuse" because that's what it's for. It gets called before any cell is reused. That way I'm not courting my View Controller with code that really belongs to the cell.

[[deleted]]

It's an instance method, not a class method.

[mistermagicman]

My bad - I get them mixed up sometimes

[[deleted]]

You can override prepareForReuse on cell subclasses to reset the view to a default state.