Currently, the LoadOnDemandCollection accepts a callback of the following format in the constructor:
public LoadOnDemandCollection(Func<CancellationToken, IEnumerable> action)It is a very common scenario to populate the items asynchronously. In its current form the collection would require blocking the current thread to populate the results:
ItemsSource = new LoadOnDemandCollection((cancelationToken) =>
{
var result = new List<ItemsModel>();
try
{
var items = dataService.GetItemsAsync().Result;
// TODO: Handle the result.
return result;
}
catch (Exception e)
{
// TODO: Handle the exception.
return null;
}
});
This is not desired, as using Task.Result blocks the current thread and is considered an anti-pattern, in general.
A better approach would be to add a second overload of the constructor, allowing asynchronous calls:
public LoadOnDemandCollection(Func<CancellationToken, Task<IEnumerable>> action)This way we can use async and await in the callback instead:
ItemsSource = new LoadOnDemandCollection(async (cancelationToken) =>
{
var result = new List<ItemsModel>();
try
{
var items = await dataService.GetItemsAsync();
// TODO: Handle the result.
return result;
}
catch (Exception e)
{
// TODO: Handle the exception.
return null;
}
});According to my tests, the first blocking approach is not a problem, as the LoadOnDemandCollection starts a thread internally. That behavior is not obvious however, and using Task.Result is somewhat counterintuitive, so the second approach is much better from the user's perspective.
1. Bind the CheckedItems collection of the TreeView to the CollectionView ItemsSource.
2. there aren't any items in the TreeView initially. Add items to it
3. Start checking the checkboxes
4. The items are added to the CollectionView, still they are not visible in the control.
Currently the group descriptors provide a SortOrder property, so the groups are sorted alphabetically in descending or ascending order. We would need to cover the following scenarios:
- allow certain groups to be ordered at the top, possibly by specifying an comparer or a separate group sort property.
- show the groups in order the corresponding items appear in the ItemsSource.
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The ItemsSource of the views is populated in the ViewModel of the page. This is done in a command that is triggered by the NavigatedTo event of the page, which is forwarded via EventToCommandBehavior from the Maui Toolkit.
When using the RadCollectionView the loaded items are no longer displayed.
When the ObservableCollection of the items is completely reconstructed and reassigned the display works.
Provide a built it way to notify the parent group when the items in the nested groups are changed.
For example, there is no PropertyChanged or CollectionChanged notification that we can hook in to in order to detect updates in parent group headers when the count changes in a subgroup. Only the leaf group headers get updated, but not the parents.
- Unexpected indent at the right, Android/iOS.
- iOS only issue - width of CollectionView content continuously changes during scroll - to fill that ident and back.
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?