集合视图IOS中的像元大小未更改（在Xamarin中实现）

Question

I have a collection view that needs to have the cells fitting size to content. I use sizeForItemAtIndexPath: to set size for each cell. It's fired and works great.

Here is the problem what I am facing. The data list for collection view is changed dynamically.

• collection view has only 1 item to show and shows it in correct cell size(let's say size1 )
• next time collection view has 1 item to show again but it's different data.

In this case, the collection view doesn't show it in correct cell size. it shows in size1 I want to show next item in its own size but collection view keep original size. When item count is changed, sizeForItemAtIndexPath: is fired again. When item count is same, it's not fired.

I want it to be fired everytime.

I share some of my code.

cllSelected.Source = new SelectedItemSource(this, _selectedItems);

Above code will be called whenever there is new _selectedItems

I implemented the UICollectionViewSource as following

public class SelectedItemSource : UICollectionViewSource, IUICollectionViewDelegateFlowLayout
    {
        CatalogVC _ownerVC;
        SelectedCategoryList _selectedItems;

        public SelectedItemSource(CatalogVC ownerVC, SelectedCategoryList selectedItems)
        {
            _ownerVC = ownerVC;
            _selectedItems = selectedItems;
        }

        public override nint NumberOfSections(UICollectionView collectionView)
        {
            return 1;
        }

        public override nint GetItemsCount(UICollectionView collectionView, nint section)
        {
            return _selectedItems != null ? _selectedItems.Count : 0;
        }

        public override bool ShouldHighlightItem(UICollectionView collectionView, Foundation.NSIndexPath indexPath)
        {
            return true;
        }

        public override void ItemHighlighted(UICollectionView collectionView, Foundation.NSIndexPath indexPath)
        {

        }

        public override void ItemUnhighlighted(UICollectionView collectionView, Foundation.NSIndexPath indexPath)
        {
            _ownerVC.SelectedFilter_ItemClick(indexPath.Row);
        }

        public override UICollectionViewCell GetCell(UICollectionView collectionView, Foundation.NSIndexPath indexPath)
        {
            SelectedFilterCollectionCell cell = collectionView.DequeueReusableCell("SelectedFilterCollectionCell", indexPath) as SelectedFilterCollectionCell;
            cell.Layer.ShouldRasterize = true;
            cell.Layer.RasterizationScale = UIScreen.MainScreen.Scale;

            cell.BindDataToCell(_selectedItems[indexPath.Row]);

            return cell;
        }

        [Export("collectionView:layout:sizeForItemAtIndexPath:")]
        public CoreGraphics.CGSize GetSizeForItem(UICollectionView collectionView, UICollectionViewLayout layout, Foundation.NSIndexPath indexPath)
        {
            var text = new NSString(_selectedItems[indexPath.Row].Text);
            CGSize cellSize = new CGSize(xxx, yyy); // cellSize will be determined according to text

            return cellSize;
        }
    }

Thanks for any solution or suggestion!

Answer 1

Try to call CollectionView.ReloadData() after the data changes.

I think it will invoke the methods included in the delegate.