Unusual disabling behavior with Command buttons

I'm sorry for this being so wordy, but I want to make the situation perfectly clear. Please, if you are a WPF pro, take a look.

There are two CollectionViewSource bound to ItemsControls that use UserControl Views to display either StackPanels or custom Buttons. There is one for each side shown in the screenshot below. The problem I'm encountering is that when the parent collection property is set, all of the buttons in the DataTemplate view are disabled. Even the 2 buttons higher up are having the same problem even though they worked before my recent edits.

If I click on the form, or press any key, the buttons enable. As soon as the property is reset to a newly edited and sorted collection, they disable again. Rinse and repeat. This is what it looks like. The first frame is how it starts (gray using StackPanel), the 2nd is what it looks like when the RFS button is clicked, and the 3rd frame is what happens when I click anywhere or press a key.

I've been going in circles trying out things. The only thing that seems to work is a code-behind workaround that sets focus to one thing and then back. However, that would not be good for the user if they are trying to use one of the other dashboard items.

Since the WPF for all of this is very massive, I'll try to include just the relevant parts. These are the ItemsControls on the TabItemControl (UserControl).

        <!-- BID (SELL) DEPTH -->
        <ItemsControl Grid.Row="0" Grid.Column="0" x:Name="bidDepthList" ItemsSource="{Binding Source={StaticResource BidDepthCollection}}"
                      Visibility="{Binding Path=IsMultilegEnabled, Converter={StaticResource CollapsedConverter}}">
           <ItemsControl.ItemTemplate>
              <DataTemplate DataType="{x:Type viewmodels:DepthLevelViewModel}">
                 <v:DepthLevelRowView x:Name="BidDepthLevelRowViewControl" DataContext="{Binding}" HorizontalAlignment="Center" Margin="1,0,1,3" />
              </DataTemplate>
           </ItemsControl.ItemTemplate>
        </ItemsControl>

        <!-- ASK (BUY) DEPTH -->
        <ItemsControl Grid.Row="0" Grid.Column="1" x:Name="askDepthList" ItemsSource="{Binding Source={StaticResource AskDepthCollection}}"
                      Visibility="{Binding Path=IsMultilegEnabled, Converter={StaticResource CollapsedConverter}}">
           <ItemsControl.ItemTemplate>
              <DataTemplate DataType="{x:Type viewmodels:DepthLevelViewModel}">
                 <v:DepthLevelRowView x:Name="AskDepthLevelRowViewControl" DataContext="{Binding}" HorizontalAlignment="Center" Margin="1,0,1,3" />
              </DataTemplate>
           </ItemsControl.ItemTemplate>
        </ItemsControl>

The view being used has 4 "controls" inside of a grid. Only one of them is displayed at a time depending on the state (RFS OFF/RFS ON) and which side they are on (Sell/Buy). The others are collapsed. As you can see, this is fine.

The only common factor between them is that they have their Command set, as do most of the controls at the top that are disabling/enabling correctly. The fact that the buttons enable correctly if any mouse or keyboard action is taken tells me that the CanExecute handler is working, just not immediately. The other controls started working after I made these changes, but then the big buttons started misbehaving like the depth buttons have been doing.

I've tried using CommandManager.InvalidateRequerySuggested(); after altering the collections, but that didn't help.

NOTE: This is also happening even for something as simple as this:

<Button x:Name="TestBuyButton" Command="{x:Static ptcommands:OrderCommands.Buy}" CommandTarget="{Binding RelativeSource={RelativeSource Self}}" Content="Test Buy" />

I know the booleans are set correctly because I added test CheckBoxes to display the current value with IsChecked. And, they all enable, including the extremely basic Button, as soon as any input action is taken.

Is there something else I'm missing or a different approach I can take?

EDIT: I ended up using the Dispatcher to invoke my display update routine from the event thread over to the UI thread. The boolean values get set, but WPF still didn't requery the Command. BUT.. the CommandManager.InvalidateRequerySuggested() call then worked! The only thing I don't like about that is it sounds like a broadcast invalidation. I don't want all commands to be requeried. I just want the Buy and Sell commands to requery. I've tried all sorts of weirdness trying to get just those to work, but nothing has worked so far other than the global.

EDIT 2: It appears as though the InvalidateRequerySuggested is the way to go.

From MSDN CommandManager.InvalidateRequerySuggested:

The CommandManager only pays attention to certain conditions in determining when the command target has changed, such as change in keyboard focus. In situations where the CommandManager does not sufficiently determine a change in conditions that cause a command to not be able to execute, InvalidateRequerySuggested can be called to force the CommandManager to raise the RequerySuggested event.

This would explain why the focus changes and keypresses would cause the buttons to enable. The page also shows putting the call in a timer. Because of this, I assume it is not as resource intensive as I thought. So, I guess it's my permanent solution.

回答1:

The command that's bound to the button...is there a CanExecute delegate with it? If so, you have to raise CanExecuteChanged when that delegate should be re-evaluated. Also, make sure the implementation of CanExecute isn't broken and incorrectly returning false;

回答2:

I had to make a few changes to get the buttons to enable without focus changes.

The boolean values were being set within a method called from an event thread. I had tried calling CommandManager.InvalidateRequerySuggested along with it, but nothing happened. Eventually I thought it might have something to do with the thread. This is what ended up resolving it.

In the parent form that the tab manager class (containing the event handlers and other logic) has access to, I added an invoke method:

  Public Sub InvokeOnUiThread(ByRef uiAction As Action, Optional ByRef doAsync As Boolean = False)

     Dim dispatchObject As Dispatcher = orderTicketView.Dispatcher

     If (dispatchObject Is Nothing OrElse dispatchObject.CheckAccess()) Then
        uiAction()
     Else
        If doAsync Then
           dispatchObject.BeginInvoke(uiAction, DispatcherPriority.Normal)
        Else
           dispatchObject.Invoke(uiAction, DispatcherPriority.Normal)
        End If
     End If

  End Sub

In the tab manager event handler, I changed it to call the update routine through the invoker:

formOrderTicketView.InvokeOnUiThread(New Action(AddressOf UpdateButtons))

At the bottom of the UpdateButtons method, I added a call to the CommandManager if a change has been made that would require a requery:

CommandManager.InvalidateRequerySuggested()

I do not know what type of performance hit this would have, but apparently WPF executes it in its own way when focus changes and such. Calling it directly is the advised way to force it.

From MSDN CommandManager.InvalidateRequerySuggested:

The CommandManager only pays attention to certain conditions in determining when the command target has changed, such as change in keyboard focus. In situations where the CommandManager does not sufficiently determine a change in conditions that cause a command to not be able to execute, InvalidateRequerySuggested can be called to force the CommandManager to raise the RequerySuggested event.

Since it is working now, I am taking this as the resolution.