WPF ListBox SelectedIndex issue

the first time it is the value my code sets it to and the second time it is -1.

what do you mean by 'bounded' listbox?

if somewhere a selection of -1 index is made, the listbox has no selection. after this, you could set the selection again.

so you could do the following:

instead of setting the selected index in the first case, you only save the index to select in a member variable or some other shared variable. when the change event with -1 was occuring you now set the selected index. be aware that the event was fired again after this.

if you want to find out which statement was causing the reset of the listbox you may add a static control to your form. in your code now write log messages to the static control at points where you think the listbox might get changed. if the -1 was selected, you break in the debugger and can see from the current log message which statement may have issued the reset of the listbox. you also can see into the stack where you should see perhaps which messages have been processed before. perhaps you have to add further log messages (or use a listbox for the messages) to narrow down the crucial code sequence..

Sara

Hello Sara,

I mean the listbox is data-bound to a Collection:

		listCues.ItemsSource = theCueList
		listCues.DisplayMemberPath = "DisplayLine"
		Dim sortDecsription As New SortDescription("ID", ListSortDirection.Ascending)
		listCues.Items.SortDescriptions.Add(sortDecsription)

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instead of setting the selected index in the first case ...

If my code does not set the selected index the change to -1 does not happen so your suggested work-around cannot be used.

if you want to find out which statement  ...

I have used the debugger to stop when the "selected index changed" event occurs, looking at the call stack does not show where the "-1" coming from. It appears that the -1 gets set very quickly after I see the right value gets set and the code has not returned to my code before the -1 is set.

This is very confusing, thanks for helping,
Sid

Sara,
I am not sure if this helps but I made a DebugView log of the issue. First a short description of the path to selecting the list item.

My "Sequencer" class detects that a change of selection is required and it raises an event to request this is done. The "PlayManager" class catches this event and in turn raises an event to request the the listbox item selection. In the "MainWindow this last event is processed and the listbox selection is made. I added messaging before and after each "RaiseEvent", plus in the "MainWindow" processing of the selection:

[5240] Sequencer::SequenceFromThisCue (Before event) - selected cue 3 
[5240] PlayManager::HandleSelectThisCue (Before event) - selected cue 3 
[5240] MainWindow::HandleSelectThisCue (Entry) - selected cue 3 
[5240] MainWindow::HandleSelectThisCue - selected cue index2 Calling listCues.SelectedIndex = cueIndex 
[5240] MainWindow::listCues_SelectionChanged - selected index 2 
[5240] MainWindow::HandleSelectThisCue - selected cue index2 After listCues.SelectedIndex = cueIndex 
[5240] MainWindow::HandleSelectThisCue (Exit) - selected cue 3 
[5240] PlayManager::HandleSelectThisCue (After event) - selected cue 3 
[5240] MainWindow::listCues_SelectionChanged - selected index -1 
[5240] Sequencer::SequenceFromThisCue (After event) - selected cue 3 

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The only place in my project that the selected index is changed is in "MainWindow" class and as you can see that method is only called once and with the correct selection.

Note that the "SelectionChanged" event is happening twice, once when I select the item requested and once to -1 so some reason.

I hope this helps understand what I am seeing.
Thanks again,
Sid

MainWindow::listCues_SelectionChanged - selected index -1

could it be that it happened cause the data were reloaded from database? do you have any Code which makes the bound control 'dirty'?

If my code does not set the selected index the change to -1 does not happen so your suggested work-around cannot be used.

you could set the selected index a second time when -1 was selected ... that is not nice but might work.

Sara

could it be that it happened cause the data were reloaded ...

No the Collection is loaded once on startup from a file.

you could set the selected index a second time ...

Well this is a pretty awful hack but at least I can move forward with my design while I continue to try to find the real solution. Here's what I added to the changed event:

	Private useThis As Integer
	Private Sub listCues_SelectionChanged(sender As Object, e As SelectionChangedEventArgs) Handles listCues.SelectionChanged
		Dim iIndex As Integer = listCues.SelectedIndex
		If iIndex = -1 Then
			listCues.SelectedIndex = useThis
		Else
			useThis = iIndex
		End If
		Debug.WriteLine("MainWindow::listCues_SelectionChanged - selected index " & iIndex)
	End Sub

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Any further ideas on the real problem here would be much appreciated,
Sid

ok. if we take for granted that your first selection also is the trigger for the reset, you first should guarantee that

   - the select is the last statement operating at the listbox in the function
     MainWindow::HandleSelectThisCue

  - that the handler MainWindow::listCues_SelectionChanged  does nothing for this case

  - and returns 'Event successfully handled' if that is possible.

Sara

the select is the last statement operating  ...

Here is the full code of MainWindow::HandleSelectThisCue:

	Private Sub HandleSelectThisCue(ByVal sender As Object, ByRef thisCue As Cue) Handles mPlayManger.SelectThisCue
		If theCueList.Contains(thisCue) = True Then
			Dim cueIndex As UInt32 = theCueList.IndexOf(thisCue)
			listCues.SelectedIndex = cueIndex
		End If
	End Sub

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that the handler MainWindow::listCues_SelectionChanged  does nothing for this case

Not sure what this means, I posted the full code of MainWindow::listCues_SelectionChanged previously.

and returns 'Event successfully handled' if that is possible

The events are "Sub" methods so there is no return value.

Sid

native winapi allows to stop a cascade of windows messages ...

This is a vb.net/WPF application, one cannot have return values on events.

how do you guarantee that an index valid for theCueList also is valid for listCues ?

The listbox is sorted by the Cue identity and these are always ascending in the input file that is read into the Collection.

can you post all functions where  listCues was used somehow?

	Private Sub MainWindow_Initialized(sender As Object, e As EventArgs) Handles Me.Initialized
		'
		' Test the cues loading
		'
		theCueList.Load("C:\DataRoot\Projects\cueassistv2.0\CueAssistv2.0\CueAssistv2.0\Shows\AvianAmb_001.aap")
		mPlayManger.CueList = theCueList
		listCues.ItemsSource = theCueList
		listCues.DisplayMemberPath = "DisplayLine"
		Dim sortDecsription As New SortDescription("ID", ListSortDirection.Ascending)
		listCues.Items.SortDescriptions.Add(sortDecsription)
	End Sub

	Private Sub btnPlaySelected_Click(sender As Object, e As RoutedEventArgs) Handles btnPlaySelected.Click
		If listCues.SelectedIndex <> -1 Then
			Dim oCue As Cue = listCues.Items(listCues.SelectedIndex)
			mPlayManger.PlayFromThis(oCue)
		End If
	End Sub

	Private Sub HandleSelectThisCue(ByVal sender As Object, ByRef thisCue As Cue) Handles mPlayManger.SelectThisCue
		If theCueList.Contains(thisCue) = True Then
			Dim cueIndex As UInt32 = theCueList.IndexOf(thisCue)
			listCues.SelectedIndex = cueIndex
		End If
	End Sub

	Private Sub listCues_SelectionChanged(sender As Object, e As SelectionChangedEventArgs) Handles listCues.SelectionChanged
		Dim iIndex As Integer = listCues.SelectedIndex
		If iIndex = -1 Then
			listCues.SelectedIndex = useThis
		Else
			useThis = iIndex
		End If
	End Sub

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I came to the fix through my own research and work.

Congratulations. It is great that you found a good solution and could remove the hack.

Sara