更新section header (UICollectionReusableView)中的文本

Question

如何更新UICollectionView节标题?在我的集合视图中，部分的标题(title)显示每个部分上可用的项目总数，当用户从集合中删除项目时，我需要更新标题。

我正在实现数据源方法collectionView:viewForSupplementaryElementOfKind:atIndexPath:，为我的集合视图中的每个部分设置自定义标题，如下所示:

- (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;
}

我的删除函数如下:

- (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*/
}

我的应用程序可以在应用程序启动时设置集合视图中的项目数量，但从集合视图中删除项目后，标题不会更新。

请建议

Answer 1

经过多次尝试，我想出了以下解决方案:

为每个section补充元素设置一个标签值…然后可以通过标签搜索对象:

- (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];
    }
}

在我个人看来，我认为它不应该是去更新UICollectionView中的任何section补充元素的方式。

另一个选择是调用reload sections，但这不仅会重新加载补充元素(header, footers)，还会重新加载每个section的数据，这可能会导致性能问题:

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

希望这可以帮助任何人在未来或张贴更好的方法:)

Answer 2

如果你有一个NSIndexPath在你的手中，当你想改变头，你可以通过调用

检索它

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

，然后使用tag属性或使用

检索标签

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

如果你有子视图在标题中添加的顺序。

欢呼。