Failed to get the correct index for UICollectionViewCell

Question

Here's the background: I have a UICollectionView which contains UITableView as its cell. Whenever I select UITableViewCell, I want to know which UICollectionViewCell the action is from.

But I fail to get the right index of UICollectionViewCell. As the code below.

First, in the init method, I register my custom cell.

 [self registerClass:[QuestionCVCell class] forCellWithReuseIdentifier:QuestionCVCellIdentifier];

Then, in the UICollectionViewDataSource.

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = nil;
        cell = (QuestionCVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:QuestionCVCellIdentifier forIndexPath:indexPath];
        if (_questions && _questions.count > 0) {
            ((QuestionCVCell *)cell).model = [_questions objectAtIndex:indexPath.item];
            ((QuestionCVCell *)cell).index = indexPath.item;

            NSLog(@"   %ld, %ld",(long)indexPath.item, (long)indexPath.row);
        }
       return cell;
}

The log is in mess, and not same as the right index I meant. I guess it has something to do with the dequeueReusableCellWithReuseIdentifier?

In code above, cell.index is passed to QuestionCVCell, which contains a tableview. I add a notification poster in its didSelectRowAtIndexPath: delegate to let main controller know that the select is from which collectionview cell.

This is the whole process of my problem.

I've searched for similar questions in Google, and find some solutions like these:

• Get the index from delegate of UIScrollView;
• Get the index by the point you touch, using indexPathForItemAtPoint: or similar methods.
• Someone said that it should be indexPath.item in collectionview instead of indexPath.row, so I logged both of them and didn't see the difference.

So my question is:

• Is there a direct way to get the correct index of UICollectionView? Why I get the right model by [_questions objectAtIndex:indexPath.item] but the wrong index by indexPath.item ?

• Is there any better way to let main controller know that the tableview cell select action belong to which collectionview cell?

• If you find any problem or mistake in my solution, please do let me know.

Thanks in advance if anyone could help with it.

Answer 1

I give you sample collection view code.It helps you get the index.

in viewDidLoad

 UINib *cellNib = [UINib nibWithNibName:@"QuestionCVCell" bundle:nil];
 [collectionView registerNib:cellNib forCellWithReuseIdentifier:@"cvCell"];

in CollectionView Data Source Methods

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
 static NSString *cellIdentifier = @"cvCell";
 QuestionCVCell *cell = (QuestionCVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
 //Here you need to give your QuestionCVCell data instead of my data;
 cell.img_Collection.image = [imgArray objectAtIndex:indexPath.row];
 cell.lbl_Collection.text = [lblArray objectAtIndex:indexPath.row];
 NSLog(@"The current indexPath row is - %ld",(long)indexPath.row);
 cell.tag = indexPath.row;
 return cell;
}

in Collection View Delegate method

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
  NSLog(@"The touched index path os collection cell item row is - %ld",(long)indexPath.row);
}

Answer 2

instead of using indexPath.row use indexPath.item in UICollectionView. it will give you correct index.

NSIndexpath.item vs NSIndexpath.row

Answer 3

Use the delegate pattern to achieve this.

i) In CollectionView Data Source Methods set the cell tag as indexPath.row

 - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    QuestionCVCell *cell = (QuestionCVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:QuestionCVCellIdentifier forIndexPath:indexPath];

    if (_questions && _questions.count > 0) {
        cell.model = [_questions objectAtIndex:indexPath.item];
    }
    cell.delegate = self;
    cell.tag = indexPath.row;
    return cell;
}

ii) Create a custom delegate in QuestionCVCell class

@protocol QuestionCVCellDelagate <NSObject>
- (void)tableSelectedWithIndex:(NSUInteger)index;
@end

@interface QuestionCVCell : UICollectionViewCell
@property (nonatomic, weak) id<QuestionCVCellDelagate>delegate;
@end

iii) In tableView didSelectRowAtIndexPath method invoke the delegate method

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    if (self.delegate && [self.delegate respondsToSelector:@selector(tableSelectedWithIndex:)]) {
        [self.delegate tableSelectedWithIndex:self.tag];
    }
}

iii) Adopt the protocol in the ViewController class and add the delegate method.

- (void)tableSelectedWithIndex:(NSUInteger)index {
    //do whatever you with the index.
}

Now whenever the table row is selected, it calls the tableSelectedWithIndex method with collection view index in ViewController class