WPF, UserControl, and Commands? Oh my!
- by Greg D
(This question is related to another one, but different enough that I think it warrants placement here.)
Here's a (heavily snipped) Window:
<Window x:Class="Gmd.TimeTracker2.TimeTrackerMainForm"
xmlns:local="clr-namespace:Gmd.TimeTracker2"
xmlns:localcommands="clr-namespace:Gmd.TimeTracker2.Commands"
x:Name="This"
DataContext="{Binding ElementName=This}">
<Window.CommandBindings>
<CommandBinding Command="localcommands:TaskCommands.ViewTaskProperties"
Executed="HandleViewTaskProperties"
CanExecute="CanViewTaskPropertiesExecute" />
</Window.CommandBindings>
<DockPanel>
<!-- snip stuff -->
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<!-- snip more stuff -->
<Button Content="_Create a new task" Grid.Row="1" x:Name="btnAddTask" Click="HandleNewTaskClick" />
</Grid>
</DockPanel>
</Window>
and here's a (heavily snipped) UserControl:
<UserControl x:Class="Gmd.TimeTracker2.TaskStopwatchControl"
xmlns:local="clr-namespace:Gmd.TimeTracker2"
xmlns:localcommands="clr-namespace:Gmd.TimeTracker2.Commands"
x:Name="This"
DataContext="{Binding ElementName=This}">
<UserControl.ContextMenu>
<ContextMenu>
<MenuItem x:Name="mnuProperties" Header="_Properties" Command="{x:Static localcommands:TaskCommands.ViewTaskProperties}"
CommandTarget="What goes here?" />
</ContextMenu>
</UserControl.ContextMenu>
<StackPanel>
<TextBlock MaxWidth="100" Text="{Binding Task.TaskName, Mode=TwoWay}" TextWrapping="WrapWithOverflow" TextAlignment="Center" />
<TextBlock Text="{Binding Path=ElapsedTime}" TextAlignment="Center" />
<Button Content="{Binding Path=IsRunning, Converter={StaticResource boolToString}, ConverterParameter='Stop Start'}" Click="HandleStartStopClicked" />
</StackPanel>
</UserControl>
Through various techniques, a UserControl can be dynamically added to the Window. Perhaps via the Button in the window. Perhaps, more problematically, from a persistent backing store when the application is started.
As can be seen from the xaml, I've decided that it makes sense for me to try to use Commands as a way to handle various operations that the user can perform with Tasks. I'm doing this with the eventual goal of factoring all command logic into a more formally-defined Controller layer, but I'm trying to refactor one step at a time.
The problem that I'm encountering is related to the interaction between the command in the UserControl's ContextMenu and the command's CanExecute, defined in the Window. When the application first starts and the saved Tasks are restored into TaskStopwatches on the Window, no actual UI elements are selected. If I then immediately r-click a UserControl in the Window in an attempt to execute the ViewTaskProperties command, the CanExecute handler never runs and the menu item remains disabled. If I then click some UI element (e.g., the button) just to give something focus, the CanExecute handlers are run with the CanExecuteRoutedEventArgs's Source property set to the UI element that has the focus.
In some respect, this behavior seems to be known-- I've learned that menus automat
