Refresh Scroll position of WPF ComboxBox on ItemSource's reload

Question

I have a ComboBox which uses ListBox to show items. ListBox’s ItemSource is bound with a CollectionViewSource.

Issue: Once I open ComboBox and scroll through the items and leave it in middle or at bottom. Once I reopen ComboBox, even though I refresh or reload ItemSource (CollectionViewSource), the Scrollbar remains at the same place where I left it last time. I want it to be as default (at top) each and every time I reload ItemSource.

Is there is any way of doing this in XAML itself? Another thing, I cannot use Behavior or Attach property. I want any template or style for this.

Why can't you use Attached Behaviors / Attached Properties? – Isaiah Nelson May 24 '16 at 22:08 — Isaiah Nelson, May 24 '16 at 22:08

score 1 · Answer 1 · edited May 23 '17 at 12:07

In order for a Style on a ListBox to embody some behavior for the <ScrollViewer>, you would need to use an Attached Property / Attached Behavior to control the ScrollViewer's "grabber" position. This is because your collection is bound to your ListBox and notifying when it is updated needs to drive a behavior that isn't natively on the ListBox. It may be possible to reset the scroll position with a <ControlTemplate> for the <ScrollViewer> itself, but I imagine it would be difficult as it would likely involve manipulating Transforms / StoryBoards based on DataTriggering with your ItemsSource, but again that may cause a dependency on needing to use an Attached property, which for some reason you can't use...

If you simply want to get a result now, and you don't care about testability or re-usability, I would handle the TargetUpdated event in the code-behind. It's ultimately what the Attached Behavior would end up doing. On the other hand, if you do care about re-usability then you need to evaluate and challenge why you can't use an Attached Behavior (they are also testable, too); an Attached Behavior would be also easier than trying to edit a ControlTemplate.

Here is the code-behind approach:

.xaml:

<ListBox x:Name="myListBox" 
        ItemsSource="{Binding MyItemsSource, NotifyOnTargetUpdated=True}"
        TargetUpdated="ListBox_TargetUpdated"/>

.xaml.cs:

private void ListBox_TargetUpdated(object sender, DataTransferEventArgs e)
{
    if (myListBox.Items.Count > 0)
        myListBox.ScrollIntoView(myListBox.Items[0]);
}

Edit: On the flip-side, if you are using MVVM, you can do something like this SO post suggests and set IsSynchronizationWithCurrentItem="True" and when you refresh your ItemsSource, simply set your SelectedItem to the first in the list and handle the SelectionChanged event in your vm.

Refresh Scroll position of WPF ComboxBox on ItemSource's reload

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