UITableView Index Path Behavior Acting Strange

Question

So I have a table view with about 150ish rows in the cellForRowAt method I have the following code

cell.monthLabel.text = String(indexPath.row)
    
if indexPath.row == 0{
    cell.backgroundColor = .blue
}

The question is why at index path 9, 18, 27 and so on have the background color of blue.

score 2 · Accepted Answer · answered May 26 '17 at 21:00

2

Cell are reused, you have to set all UI elements to a defined state.

So if you set the backgroundColor to blue in row 0

if indexPath.row == 0 {
    cell.backgroundColor = .blue
}

you have to (re)set it to a default color in all other cases

else {
    cell.backgroundColor = .white
}

answered May 26 '17 at 21:00

vadian

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1

Thanks that solved my issue, but out of curiosity would you happen to know why it was every 9 cell instead of every cell being blue? – Ross Sullivan May 26 '17 at 21:10
3

You got 7 cells on screen plus 2 prepared – one on the top and one on the bottom – when the user scrolls. – vadian May 26 '17 at 21:16

score 1 · Answer 2 · answered May 26 '17 at 20:49

As you do not show all the code of the tableView(_:cellForRowAt:) method just assume you are dequeuing cells (with the method dequeueReusableCell(withIdentifier:) and have registered you class for reusing (if you use a custom class).

With this approach the view of the cells gets reused. Meaning that if you do not re-set a property (e.g. background color) it will just use the one form the old cell.

To fix this you can easily include a else in your code and in there set the background color to white.

If you subclass the UITableViewCell class you can the prepareForReuse() function to clean up and e.g. reset the background color.

score 0 · Answer 3 · answered May 26 '17 at 21:08

UITableView doesn't set the data on each item once, it keeps setting the data again and again on all visible items according to the activity going on. i can't give you the clear reason for this behavior but I can give you the solution. Whenever you are setting some data on items with some conditions, always use "Else" statement as well. So for this particular issue you just have to do is to add "Else" block with your "If" condition and set the white background of item in "Else" block.

UITableView Index Path Behavior Acting Strange

3 Answers3