how to reload supplementary view in collectionView

Question

Is there an easy way to reload the suppplementary view only in a UICollectionViewFlowLayout? I don't want to reload the whole thing. Is it possible to do so?

Answer 1

After reviewing the documentation, I'm not sure about reloading an individual supplementary view, but you can use reloadSections: to update 1 or more sections in the UICollectionView. ( documentation ) So when a section header needs updating, you can call:

Objective-C:

[self.collectionView reloadSections:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 3)]];

Swift:

self.collectionView?.reloadSections(IndexSet(0 ..< 3))

Which happens to call:

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

       //Place logic for handling update here...
}

Answer 2

如果要从Controller更改补充视图的布局或大小，请使用[self.collectionView.collectionViewLayout invalidateLayout] 。如果只想刷新补充视图，请使用[supplementaryView setNeedsDisplay]如果补充视图为复杂和/或将更改其尺寸。