We have an issue in which a RadComboBox configured with VirtualizingStackPanel
and using an ItemsSource of VirtualQueryableCollectionView, sometimes doesn't load items, especially when scrolling to the end of it.
For example, when the combo-box drop-down is opened and initial items are loaded,
If you scroll straight to the end of the combo-box using the vertical scroll-bar,
the ItemLoading event won't be triggered in the VirtualQueryableCollectionView that uses as the ItemsSource.
The scenario is when loading items async (without RIA).
Telerik documentation declare the RadComboBox suppose to work with VirtualQueryableCollectionView
http://www.telerik.com/help/silverlight/using-data-virtualization.html
So my question is, is it RadComboBox / VirtualQueryableCollectionView issue or
is it incorrectly practicing the data virtualization (as shown in the attached sample)?
Thanks
-Attached is a sample that demonstrate the problem-
--The View--
The view-model
The rest
internal class ItemsDataLoader
{
public void GetItemsAsync(int startIndex, int itemCount, Action<ItemsAsyncCallResult> completionCallback, object userState)
{
var random = new Random();
int delayMilliseconds = random.Next(10, 1000);
AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null); //remember the calling thread
Timer timer = null;
TimerCallback callback = delegate
{
OnTimerTriggered(timer, asyncOp, startIndex, itemCount, completionCallback, userState);
};
timer = new Timer(callback, null, delayMilliseconds, Timeout.Infinite);
}
private void OnTimerTriggered(Timer timer, AsyncOperation asyncOp, int startIndex, int itemCount, Action<ItemsAsyncCallResult> completionCallback, object userState)
{
timer.Dispose();
IEnumerable<DataItem> items = LoadItems(startIndex, itemCount);
var result = new ItemsAsyncCallResult(items, userState);
SendOrPostCallback callbackOnOriginalThread = arg => completionCallback(result);
asyncOp.PostOperationCompleted(callbackOnOriginalThread, null);
}
private IEnumerable<DataItem> LoadItems(int startIndex, int itemCount)
{
var items = new List<DataItem>();
for(int index = startIndex; index < startIndex + itemCount; index++)
{
var item = new DataItem
{
Id = index + 1001,
Score = (index % 101),
Text = "Item No " + (index + 1)
};
items.Add(item);
}
return items;
}
}