Swift: Table Cells not setting up buttons correctly - ios

Question

I have been following a tutorial online for a yikyak clone using swift and parse. i am storing the objectIDs of the upvoted/downvoted items using coreData. When the tableview cell is loaded, it checks if the objectID on parse is in coreData and responds accordingly by adding a background image to the specific button and disabling both the up and down vote buttons. However, I am facing an issue where scrolling up and down a few times causes random cells to have the background and have their buttons disabled.
Here is a link to the code (cellForRowAtIndexPath:):
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as PullTableViewCell
let restaurant = self.restaurantData[indexPath.row]
cell.scoreLabel.text = "\(score)"
cell.plusButton.tag = indexPath.row;
cell.plusButton.addTarget(self, action: "plusOne:", forControlEvents: .TouchUpInside)
cell.minusButton.tag = indexPath.row
cell.minusButton.addTarget(self, action: "minusOne:", forControlEvents: .TouchUpInside)
if (cell.plusButton.enabled) {
// upvotes
let request = NSFetchRequest(entityName: "Upvotes")
let moc:NSManagedObjectContext = self.managedObjectContext!
var error: NSErrorPointer = nil
self.upvoteData = moc.executeFetchRequest(request, error: error) as [Upvotes]
for (var i = 0; i < self.upvoteData.count; i++) {
if (self.upvoteData[i].objectid == self.objectIDs[indexPath.row]) {
NSLog("the cell is in view is \(indexPath.row)")
cell.plusButton.backgroundColor = UIColor.blueColor()
cell.minusButton.enabled = false
cell.plusButton.enabled = false
}
}
// downvotes
let request2 = NSFetchRequest(entityName: "Downvotes")
let moc2:NSManagedObjectContext = self.managedObjectContext!
var error2: NSErrorPointer = nil
self.downvoteData = moc2.executeFetchRequest(request2, error: error2) as [Downvotes]
for (var i = 0; i < self.downvoteData.count; i++) {
if (self.downvoteData[i].objectid == self.objectIDs[indexPath.row]) {
cell.minusButton.backgroundColor = UIColor.blueColor()
cell.minusButton.enabled = false
cell.plusButton.enabled = false
}
}
}
return cell
}
Does it have to do with asynchronous processing?

Answer 1

The tableview actually re-creates cells on the fly as you scroll up and down. So when a cell is scrolled out of view it can get destroyed and re-created.
You need to store cell properties inside of a map and then re-initialize the cell each time.
Here is an example from my own code:
public func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
{
var cell = collectionView.dequeueReusableCellWithReuseIdentifier("selectPhotoCell", forIndexPath: indexPath) as B_SelectPhotoControllerViewCell
cell.indexPath = indexPath
let asset = currentAssetAtIndex(indexPath.item)
PHImageManager.defaultManager().requestImageForAsset(asset, targetSize:_cellSize, contentMode: .AspectFit, options: nil)
{
result, info in
if(cell.indexPath == indexPath)
{
cell.imageView.image = result
cell.imageView.frame = CGRectMake(0, 0,self._cellSize.width,self._cellSize.height)
for editImage in self._editImageChicklets
{
if(editImage.selectedPhotoIndexPath != nil && editImage.selectedPhotoIndexPath == indexPath)
{
cell.number = editImage.selectedPhotoDisplayNumber!
}
}
}
}
return cell
}
This is an example of a UICollectionView that uses photo images from the users photo roll. I keep track of the indexPath, and if its a match, then I assign the images to the property.
In your case you need to do the same. Keep a map of the cell properties and the index path:
Dictionary<NSIndexPath,CustomCellPropertiesObject>
Then go through and re-initialize it appropriately.