Programmatically multiselection update is slow in listbox.

Question

I try to programmatically update the selected items in a listbox, with extended selection mode.
Here is how I do it:

foreach (var selectedItem in ItemsForSelection)
{
  _myList.SelectedItems.Add(selectedItem);
}

My problem is, that when the number of the selected items is big, the update is very slow.
The root of the problem is that listbox doesn't derrive from MultiSelector, which can be tweaked to perform a fast bulk update, by using the methods BeginUpdateSelectedItems and EndUpdateSelectedItems.
Is there a way to get a similar result in a listbox?

Answer 1

Is there a BeginUpdate and EndUpdate method available in the ListBox...

_myList.BeginUpdate();
foreach (var selectedItem in ItemsForSelection)
{
  _myList.SelectedItems.Add(selectedItem);
}
_myList.EndUpdate();

That is assuming that _myList is a ListBox...The pair for Begin/End Update methods freezes the WM_PAINT message and unfreezes respectively thereby making it flicker free and fast.

Hope this helps, Best regards, Tom.

Answer 2

After adding a chunk of items, try pumping the dispatcher by pushing a dispatcher frame into the dispatcher.

http://msdn.microsoft.com/en-us/library/system.windows.threading.dispatcherframe.aspx

Answer 3

There is a SetSelectedItems(IEnumerable) available on ListBox you could use. This function wraps selection changes in a SelectionChange.Begin/End (unfortunately only available internally of course) which ought to result in only a single selection change event going out.

Note that SetSelectedItems is protected, so you'll have to use your own ListBox derivative to call it. Odd choice, that.