Update text in section header (UICollectionReusableView)

Question

How can I update UICollectionView section title? Headers (titles) for sections in my collection view show the total number of items available on each section and I need to update that title when the user has deleted items from the collection.

I'm implementing datasource method collectionView:viewForSupplementaryElementOfKind:atIndexPath: to set a custom header for each one of the sections in my collection view, as follows:

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionReusableView *view = nil;

    if([kind isEqualToString:UICollectionElementKindSectionHeader]) {

        view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"myCustomCollectionHeader" forIndexPath:indexPath];

        MyCustomCollectionViewHeader *header = (MyCustomCollectionViewHeader *) view;

        NSString *headerTitle;

        if(indexPath.Section == 0) {
            headerTitle = [NSString stringWithFormat:@"%lu items", (unsigned long) myArrayOfObjectsInFirstSection.count];
        } else {
            headerTitle = [NSString stringWithFormat:@"%lu items", (unsigned long) myArrayOfObjectsInSecondSection.count];
        }

        header.myLabelTitle.text = headerTitle;
    }
    return view;
}

My delete function is as follows:

- (void)deleteSelectedItems {

    NSArray *indexPaths = self.collectionView.indexPathsForSelectedItems;

    for(NSIndexPath *indexPath in indexPaths) {

        NSString *numberOfItems;

        if(indexPath.section == 0) {
            [myArrayOfObjectsInFirstSection removeObjectAtIndex:indexPath.row];
            numberOfItems = [NSString stringWithFormat:@"%lu items", (unsigned long)myArrayOfObjectsInFirstSection.count];
        } else {
            [myArrayOfObjectsInSecondSection removeObjectAtIndex:indexPath.row];
            numberOfItems = [NSString stringWithFormat:@"%lu items", (unsigned long)myArrayOfObjectsInSecondSection.count];
        }

        [self.collectionView deleteItemsAtIndexPaths:@[indexPath]];
    }
    /* after deleting all items, section title must be updated with the new value of numberOfItems*/
}

My app is able to set the number of items in collection view when the app starts, but after deleting items from collection view the header doesn't get updated.

Please advice

score 3 · Accepted Answer · answered Jun 26 '14 at 21:19

After many multiple attempts I came up with the following workaround:

Set a tag value for each section supplementary element... then later it's possible to search the object by tag:

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionReusableView *view = nil;

    if([kind isEqualToString:UICollectionElementKindSectionHeader]) {

        view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"myCustomCollectionHeader" forIndexPath:indexPath];

        MyCustomCollectionViewHeader *header = (MyCustomCollectionViewHeader *) view;

        if(indexPath.Section == 0) {
            header.tag = 100;
        } else {
            header.tag = 200;
        }

        // ...

    }
    return view;
}

- (void)updateSectionTitles {
    NSInteger numberOfItems;
    MyCollectionViewHeader *header;
    if(indexPath.section == 0) {
        header = (MyCollectionViewHeader *) [self.collectionView viewWithTag:100];
        numberOfItems = myArrayOfObjectsInFirstSection.count;
    } else {
        header = (MyCollectionViewHeader *) [self.collectionView viewWithTag:200];
        numberOfItems = myArrayOfObjectsInSecondSection.count;
    }
    header.myHeaderTitleLabel.text = [NSString stringWithFormat:@"There are %lu items", (unsigned long) numberOfItems];
    }
}

In my personal opinion I think it shouldn't be the way to go to update any section supplementary element in UICollectionView.

Another option is to call reload sections, but this reloads not only supplementary elements (headers, footers) but also the data of each section which may be a performance issue:

[self.collectionView reloadSections:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 2)]];

Hope this may help anybody in the future or post with better approach :)

score 2 · Answer 2 · answered Jul 22 '16 at 17:12

2

If you have an NSIndexPath in your hands when you want to change de header, you can retrieve it by calling

let header = self.collectionView?.supplementaryViewForElementKind(UICollectionElementKindSectionHeader, atIndexPath: indexPath_)

and then retrieve your labels using the tag property or using

let _label = header!.subviews[0] as! UILabel

if you have the order that the subviews were added in the header.

Cheers.

answered Jul 22 '16 at 17:12

reinaldoluckman

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the `header` always seems to be nil.. as I am performing the operation in `willDisplaySupplementaryView`. I guess at that moment, the view is not initialized yet? – nr5 Oct 05 '17 at 18:26

Update text in section header (UICollectionReusableView)

2 Answers2