ListBox Shift-Click Multi-Select Anchor is not bei

Question

I’m at my wit’s end trying to figure this out. I'm experienced in WPF, but I've never seen anything like this.

I have a ListBox that contains selectable ListBoxItems. Items in the list can be selected by mouse click or by using the up/down arrows. I’m using SelectionMode.Extended, so my list supports multiple selections.

The problem: Clicking on an item in the list, then Shift-Clicking on another item selects the correct range of items like you would expect. Unfortunately, using the up/down arrows does not work properly – instead, the range that’s selected always seems to be based off of the last CLICKED item, not the item that was selected with the arrow keys.

For example:

[Item 1] <- Click this item
[Item 2] <- Use the down arrow to select this item
[Item 3] <- Shift-Click this item

You would expect items 2 and 3 to be selected, instead, all of the items (1, 2, and 3) are selected.

All of the ListBox properties have the correct values (i.e. using the arrow keys updates the SelectedItems property), my only problem seems to be with how the ListBox is handling Shift-Click selection internally. To the best of my knowledge, I believe this has to do with the ListBox’s “multi-select anchor” getting set by mouse-click but not with the arrow keys.

Has anyone encountered and solved this before? Is there a way to set the “multi-select anchor” manually? Thanks for your help!

Chris

Answer 1

I've figured out the resolution to this:

In order to solve this, you must set Focus to the item after changing the SelectedIndex:

if (SelectedIndex > 0) {
     SelectedIndex--;
     ListBoxItem item = ItemContainerGenerator.ContainerFromIndex(SelectedIndex) as ListBoxItem;
     item.Focus();
}

This is how you move the selection down in the list. However, you need to set focus to the item for the shift-click selection to recognize the item as the anchor.