UICollectionView - didDeselectItemAtIndexPath not called if cell is selected

Question

The first thing I do is to set the cell selected.

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    cell.selected = YES;
    return cell;
}

And the cell is successfully selected. If the user touches the selected cell, than should the cell be deselected and the delegates be called. But this never happen.

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"%s", __PRETTY_FUNCTION__);
}

- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"%s", __PRETTY_FUNCTION__);
}

I know that the delegates are not called if I set the selection programmatically. The delegate and datasource are set.

However, this delegate gets called:

- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"%s", __PRETTY_FUNCTION__);
    return YES;
}

If I remove the cell.selected = YES than everything is working. Is there any one who can me explain this behaviour?

Answer 1

The issue is, that the cell is selected, but the UICollectionView does not know anything about it. An extra call for the UICollectionView solves the problem:

[collectionView selectItemAtIndexPath:indexPath animated:NO scrollPosition:UICollectionViewScrollPositionNone]; 

Full code:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    cell.selected = YES;
    [collectionView selectItemAtIndexPath:indexPath animated:NO scrollPosition:UICollectionViewScrollPositionNone];
    return cell;
}

I keep the question to help someone who may face the same problem.

Answer 2

I think the solution @zeiteisen provided is a way around solution. The actual thing lies in the selection mode. There is nothing to be set the in property cell.selected .

There are two properties of the UICollectionView name allowsMultipleSelection and allowsSelection .

allowsMultipleSelection is NO by default and allowsSelection is YES .

If you want to select only one cell then the code @the initialization look like

yourCollectionView.allowsMultipleSelection = NO;
yourCollectionView.allowsSelection = YES; //this is set by default

Then the settings will allow you select only one cell at a time, not less not more. You must have to select at least one cell. The didDeselectItemAtIndexPath wont be called unless you select another cell. Tapping an already selected UICollectionViewCell won't make it to Deselect. This is the policy behind the implementation.

If you want to select multiple cell then the code @the initialization should look like the following:

yourCollectionView.allowsMultipleSelection = YES;
yourCollectionView.allowsSelection = YES; //this is set by default

Then the settings will allow to select multiple cell. This settings allow none or multiple UICollectionViewCell to be selected. Number of cell selected will be

0 <= number_selected_cell <= total_number_of_cell

This is the policy behind the multiple cell selection.

If you are intended to use any of the above you are welcome to use apples api without extra headache, otherwise you got to find a way around to sneak into your goal using your own code or apple's api.

Answer 3

I had the same issue. I pre-selected cells upon table load yet I had to double tap a cell to deselect it. @zeiteisen answer helped me. However, I'm working in Swift 3 so I thought I'd give an answer in Swift.

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell

    if /*Test for Selection*/ {
        cell.isSelected = true
        collectionView.selectItem(at: indexPath, animated: false, scrollPosition: .left)
    }        
    return cell
}

Answer 4

将此行添加到您的 didSelectItemAtIndexPath 方法中

[collectionView selectItemAtIndexPath:indexPath animated:NO scrollPosition:nil]

Answer 5

In my case, I want to change the background of the button in other words the background of the cell in the collection view:

class CustomCVCell: UICollectionViewCell {

override var isSelected: Bool {
        didSet {
            grayBackgroundViewWithImage.image =
                isSelected ? UIImage(named: "") : UIImage()
        }
    }

In the main class where the collection view is stored create this variable:

class CustomViewController: UIViewController {

///save the indexPath of last selected cell
private var lastSelectedIndexPath: IndexPath? }

In viewDidLoad() set this value to false:

customCollectionView.allowsMultipleSelection = false

Further code in data source. In my case, the first cell should be is selected:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: CustomCVCell.cellID(),
                                                  for: indexPath) as! CustomCVCell
    
    if indexPath.row == 0 {
        lastSelectedIndexPath = indexPath
        cell.isSelected = true
    }
    
    //update last select state from lastSelectedIndexPath
    cell.isSelected = (lastSelectedIndexPath == indexPath)
    
    return cell
}

Further code in the delegate:

///UICollectionViewDelegate
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    guard lastSelectedIndexPath != indexPath else { return }

         if let index = lastSelectedIndexPath {
            let cell = collectionView.cellForItem(at: index) as! CustomCVCell
            cell.isSelected = false
          }

          let cell = collectionView.cellForItem(at: indexPath) as! CustomCVCell
          cell.isSelected = true
    lastSelectedIndexPath = indexPath
}

Answer 6

Reloading the cell was solution for me. What i need was changing image in cell for a brief moment. I assign image to imageView in cellForItemAtIndexPath and when user touches the cell i change image and run mycode then reload the cell.

 func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
        let cell = collectionView.cellForItemAtIndexPath(indexPath) as! MenuCollectionViewCell
        cell.backgroundImageView.image = UIImage(named: "selected")
        // handle tap events
        collectionView.reloadItemsAtIndexPaths([indexPath])
    }

Hope it helps someone.

Answer 7

In my case it was caused by using same logic for

func collectionView(_ collectionView: UICollectionView, shouldHighlightItemAt indexPath: IndexPath) -> Bool

as for

func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool

And when cell was selected shouldHighlightItemAt was returning false - and this prevented me to deselect that cell.

Hope this will save someone's time :)

Answer 8

I was having the same issue, if you investigate further you willl see that not only the diddiselect is not called, but the touch itself is not perceived by the cell. What solved for me was to allow for async execution of the selection and set the selecItem manually as well. Inside cellForItemAt.

       DispatchQueue.main.async {
            cell.isSelected = true
            collectionView.selectItem(at: indexPath, animated: false, scrollPosition: .init())
        }

Use .init() and false on animated if you don't want to see movements. If you don't wrap this with the async block you will see the UI jumping while scrolling.