WPF Gui refresh from different Thread

Question

I have a popup Gui with command binding,

 <Grid x:Name="popup" Visibility="Hidden" DataContext="{Binding Path=PopupMsg}" >


                    <TextBlock x:Name="tbMessage" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="3" Margin="20,70,10,0"
                           Text="{Binding Path=Message}" FontSize="16"/>

                    <Button x:Name="btnPopupOk" Grid.Row="1" Grid.Column="2" Content="{Binding Path=OkContent}" Margin="10,40,10,10"
                        Command="{Binding}" CommandParameter="true" />
                </Grid>
            </Border>
        </Grid>

in the C# file i bind the command:

   CommandBinding okCommandBinding = new CommandBinding(OkCommand);
   okCommandBinding.Executed += popupButtons_Executed;
    okCommandBinding.CanExecute += okCommandBinding_CanExecute;
    CommandBindings.Add(okCommandBinding);
    btnPopupOk.Command = OkCommand;

Its working fine when I use it from the same Thread, when I get a callback from Web Service which is in a different thread I use Dispatcher to show a message, i can see the new text in the popup but the binding isn't working the button remaining unavailable (CanExecute = false), When I click on the screen with the mouse, the popup update the real value of CanExecute and the button is appear available.

System.Windows.Threading.DispatcherPriority.Normal,
          new Action(
            delegate()
            {
                popup.Visibility = Visibility.Visible;
                popup.Focus();

            }));

Why do you need to change the CommandBinding of the button ? — Thomas Levesque
– Thomas Levesque, Commented Aug 13, 2009 at 9:06
@dmitri I think that he wish to know why the commands are being updated only after he clicked on the screen. — ArielBH
– ArielBH, Commented Aug 13, 2009 at 9:19

Alastair Pitts · Accepted Answer · 2009-09-26 16:14:05Z

12

this is the code snippet I use to fix any cross thread calls when updating a WPF UI.

 this.Dispatcher.BeginInvoke(
            (Action)delegate()
        {
            //Update code goes in here
        });

Hope this helps

answered Sep 26, 2009 at 16:14

Alastair Pitts

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Cameron MacFarland · Accepted Answer · 2009-09-26 16:35:52Z

2

Your issue isn't with threading, it's with what will cause a command to call CanExecute.

Usually only certain gui events will cause routed commands to update, and since WPF doesn't know to call CanExecute when data changes, it doesn't.

To manually cause all routed commands to update, call CommandManager.InvalidateRequerySuggested. If the command is based on the message I'd call it when the message is changed.

answered Sep 26, 2009 at 16:35

Cameron MacFarland

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Thies · Accepted Answer · 2009-08-13 09:04:46Z

1

You need to use a dispatcher to get the visibility update to go through the main GUI thread (like you need to use Invoke with WinForms)

See MSDN Forums for details.

Basically something like;

   popup.Dispatcher.Invoke(DispatcherPriority.Normal, delegate() { popup.Visibilty = Visibility.Visible; popup.Focus(); });

answered Aug 13, 2009 at 9:04

Thies

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1 Comment

ArielBH Over a year ago

It's hard to tell by the question, but I think he is already doing it, based on the last code section.

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