Items do not display after scrolling, navigating to another page, and returning to the page. 

You have to scroll or resize the window and the items appear

from 11.1.0 version and above the behavior of dropping item changes for my custom scenario.

I have two CollectionView's. one on left has inner collectionview, and one on right. When the inner collectionview has no items, dropping item from the right collectionview to the collectionview with no data cannot be achieved. 

The height of the inner collectionview with no items is 0. 

This works in 11.0.0 version but after 11.1.0 the behavior changes and item cannot be dropped.

Having the following code:

    <telerik:RadCollectionView
            x:Name="configurationsCollectionView"
            BackgroundColor="Green"
            ItemsSource="{Binding Configurations}">
        <telerik:RadCollectionView.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto" />
                        <ColumnDefinition Width="*" />
                    </Grid.ColumnDefinitions>
                    <Label
                            Grid.Column="0"
                            BackgroundColor="Blue"
                            Text="Test 123" />
                    <Label
                            Grid.Column="1"
                            BackgroundColor="Red"
                            Text="Test 456" />
                </Grid>
            </DataTemplate>
        </telerik:RadCollectionView.ItemTemplate>
    </telerik:RadCollectionView>

when rotating the device, the control does not size correctly its item template

We've got a CollectionView which shows a list of grouped items (grouping can be by date or other values - but date is the default).

The CollectionView items source is bound to an observable collection, and when the viewmodel saw an item removed from the observable collection, the Telerik control crashed.  We've seen instances of this app crash on Android (the same control hasn't been released to other platforms yet). We do not have reproduction steps as this is a rare issue, but it feels like it is worth communicating as you might be able to spot what is going on from your end.

System.ArgumentException: Arg_MustBeDateTime
  at int DateTime.CompareTo(object value)()
  at int Comparer.Compare(object a, object b)()
  at int SortFieldComparer.Compare(object o1, object o2)()
  at int ArraySortHelper<object>.InternalBinarySearch(object[], int, int, object, IComparer<object>)()
  at int ArraySortHelper<object>.BinarySearch(object[], int, int, object, IComparer<object>)()

System.InvalidOperationException: InvalidOperation_IComparerFailed
  at int ArraySortHelper<object>.BinarySearch(object[], int, int, object, IComparer<object>)()
  at int Array.BinarySearch<object>(object[] array, int index, int length, object value, IComparer<object> comparer)()
  at int List<object>.BinarySearch(int, int, object, IComparer<object>) x 2()
  at int Group.IndexOf(object item, IComparer<object> sortComparer)()
  at Tuple<Group, int> ParallelDataEngine.FindGroupAndItemIndex(IValueProvider valueProvider, Group rowRootGroup, object item, int index, bool exhaustiveSearch, bool canUseComparer)()
  at AddRemoveItemResult ParallelDataEngine.RemoveItem(IAggregateResultProvider aggregateResultProvider, IValueProvider valueProvider, Group rowRootGroup, Group columnRootGroup, object item, int index, bool exhaustiveSearch, bool canUseComparer)()
  at List<AddRemoveResult> ParallelDataEngine.Process(int index, IEnumerable items, bool remove, bool removeFilteredItem, bool canUseComparer)()
  at List<AddRemoveResult> ParallelDataEngine.Telerik.Maui.Data.IDataEngine.RemoveItems(int index, IEnumerable items, bool removeFilteredItem, bool canUseComparer)()
  at List<AddRemoveResult> LocalDataSourceProvider.RemoveItems(int oldStartingIndex, IList oldItems, NotifyCollectionChangedEventArgs e, bool doExhaustiveSearch, bool canUseComparer)()
  at void LocalDataSourceProvider.ProcessCollectionChanged(NotifyCollectionChangedEventArgs e)()
  at void LocalDataSourceProvider.DataView_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)()
  at void EnumerableDataSourceView.RaiseCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)()
  at void EnumerableDataSourceView.ProcessCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)()
  at void EnumerableDataSourceView.ProcessCollectionChangedOverride(object sender, NotifyCollectionChangedEventArgs args)()
  at void EnumerableDataSourceView.ProcessPendingCollectionChange()()
  at void DataProviderBase.RaiseViewChanging(object sender, IList changedItems, CollectionChange action)()
  at void LocalDataSourceProvider.DataView_CollectionChanging(object sender, NotifyCollectionChangedEventArgs e)()
  at void EnumerableDataSourceView.RaiseCollectionChanging(object sender, NotifyCollectionChangedEventArgs args)()
  at void EnumerableDataSourceView.HandleCollectionChangedOverride(object sender, NotifyCollectionChangedEventArgs e)()
  at void EnumerableDataSourceView.Telerik.Maui.IWeakEventListener.ReceiveEvent(object sender, object args)()
  at void WeakEventHandlerList<NotifyCollectionChangedEventArgs>.ProcessEvent(object sender, object args)()
  at void WeakEventHandlerList<NotifyCollectionChangedEventArgs>.OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)()
  at void ObservableCollection<IWorkItemListItem>.OnCollectionChanged(NotifyCollectionChangedEventArgs) x 2()
  at void ObservableCollection<IWorkItemListItem>.RemoveItem(int)()
  at bool Collection<IWorkItemListItem>.Remove(IWorkItemListItem)()

any ideas on what might be going on here?

Hello,

The CollectionView has a HeaderTemplate and a FooterTemplate. When using grouping, there is a GroupHeaderTemplate but no GroupFooterTemplate (like the default MAUI CollectionView has).

Can the GroupFooterTemplate be added to the CollectionView control?

Thanks!

1. Unexpected indent at the right, Android/iOS.
2. iOS only issue - width of CollectionView content continuously changes during scroll - to fill that ident and back.

I see iOS crashes in Sentry, seems like caused by clearing the RadCollectionView bound DataSource ObservableCollection, when an item was previously selected

Maui 9.0.70
Telerik 11.0

System.NullReferenceException: Arg_NullReferenceException
  ?, in void RadCollectionViewItemView.OnIsSelectedChanged()
  ?, in static RadCollectionViewItemView()+(BindableObject b, object o, object n) => { }
  ?, in void BindableObject.OnBindablePropertySet(BindableProperty property, object original, object value, bool didChange, bool willFirePropertyChanged)
  ?, in void Element.OnBindablePropertySet(BindableProperty property, object original, object value, bool changed, bool willFirePropertyChanged)
  ?, in void BindableObject.SetValueActual(BindableProperty property, BindablePropertyContext context, object value, bool currentlyApplying, SetValueFlags attributes, SetterSpecificity specificity, bool silent)
  ?, in void BindableObject.SetValueCore(BindableProperty property, object value, SetValueFlags attributes, SetValuePrivateFlags privateAttributes, SetterSpecificity specificity)
  ?, in void BindableObject.SetValue(BindableProperty property, object value)
  ?, in void RadCollectionViewItemView.set_IsSelected(bool value)
  ?, in void RadCollectionView.SelectContainers(IEnumerable items, bool select)
  ?, in void RadCollectionView.SelectionHelperSelectionChanged(object sender, RadSelectionChangedEventArgs e)
  ?, in void <>c__DisplayClass36_0.<SelectionChangerSelectionChanged>b__0(?)+() => { }
  ?, in void ActiveSelectionScope.Dispose()
  ?, in void SelectionHelper.ClearSelection()
  ?, in void RadCollectionView.Telerik.Maui.Controls.ICollectionView.ItemsChanged(NotifyCollectionChangedEventArgs e)
  ?, in void CollectionViewModel.OnDataProviderViewChanged(object sender, ViewChangedEventArgs e)
  ?, in void DataProviderBase.RaiseViewChanged(object sender, List<AddRemoveResult> changes, NotifyCollectionChangedEventArgs args, CollectionChange action, bool affectsAggregates)
  ?, in void LocalDataSourceProvider.ProcessCollectionChanged(NotifyCollectionChangedEventArgs e)
  ?, in void LocalDataSourceProvider.DataView_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
  ?, in void EnumerableDataSourceView.RaiseCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
  ?, in void EnumerableDataSourceView.ProcessCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
  ?, in void EnumerableDataSourceView.ProcessCollectionChangedOverride(object sender, NotifyCollectionChangedEventArgs args)
  ?, in void EnumerableDataSourceView.ProcessPendingCollectionChange()
  ?, in void DataProviderBase.RaiseViewChanging(object sender, IList changedItems, CollectionChange action)
  ?, in void LocalDataSourceProvider.DataView_CollectionChanging(object sender, NotifyCollectionChangedEventArgs e)
  ?, in void EnumerableDataSourceView.HandleCollectionChangedOverride(object sender, NotifyCollectionChangedEventArgs e)
  ?, in void EnumerableDataSourceView.Telerik.Maui.IWeakEventListener.ReceiveEvent(object sender, object args)
  ?, in void WeakEventHandlerList<NotifyCollectionChangedEventArgs>.ProcessEvent(object sender, object args)
  ?, in void WeakEventHandlerList<NotifyCollectionChangedEventArgs>.OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
  ?, in void ObservableCollection<ViewBundle>.OnCollectionChanged(NotifyCollectionChangedEventArgs)
  ?, in void ExtObservableCollection<ViewBundle>.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
  ?, in void ObservableCollection<ViewBundle>.OnCollectionReset()
  ?, in void ObservableCollection<ViewBundle>.ClearItems()
  ?, in void ExtObservableCollection<ViewBundle>.ClearItems()
  ?, in void Collection<ViewBundle>.Clear()
  ?, in void SearchViewViewModel.Dispose(bool disposing)
  ?, in void PropertyChangedNotifyingBase.Dispose()
  ?, in async void ViewBundle.Dispose(bool disposing)
  ?, in void <>c.<ThrowAsync>b__128_0(?)+(object state) => { }
  ?, in void NSAsyncSynchronizationContextDispatcher.Apply()
  ?, in void __Registrar_Callbacks__.callback_3311_Foundation_NSAsyncSynchronizationContextDispatcher_Apply(IntPtr pobj, IntPtr sel, IntPtr* exception_gchandle)

When having a CollectionView and navigating between different views when tapping on an item from the CollectionView, the item(s) look(s) selected. 

It seems the behavior is due to the mouse over and selected visual states.