Factory.EventValueCommand does not handle null properly..(?) about fsharp.viewmodule

[ReedCopsey]

@ruxo The EventValueCommand is meant to be used where the CommandParameter is of the generic type of the Event type. In this case, it'd mean you'd need a converter to pass the parameter of type MainWindowEvents.

What are you trying to do? There are a couple of approaches -

1. You could use the normal command infrastructure from ViewModelBase to just create a command that accepts a string parameter, then optionally add it to your event stream if you need at that point.
2. Write a converter to convert from your actual parameter type to the event type. This is what the sample applications in FsXaml all do.

[ruxo]

I'm interested in Event Stream and trying to do MVC with it (inspired by a blog post from http://marisks.net/). In my real XAML, there is also a TreeView which I also uses for selecting item. The TreeViewItem uses EventToCommand to convert Selected event to MainWindowEvents. Like following snippet:

      <TreeViewItem Header="About sample" Tag="AboutDialog.xaml">
        <i:Interaction.Triggers><i:EventTrigger EventName="Selected"><fsx:EventToCommand Command="{Binding EventCommand}" EventArgsConverter="{StaticResource selectConverter}" /> </i:EventTrigger> </i:Interaction.Triggers>
      </TreeViewItem>

Now I'm trying to use buttons instead of the TreeView. I guess I can use EventTrigger to do the same thing but I'm curious if there is a shorter way to do so.

So I have to apply a converter. Do I have to implement it myself (something like EventArgsConverter) or is there already a helper in the library? Sorry I'm new to this library. Thank you for your help :)

[ReedCopsey]

You'd need to make your own converter. If you inherit inherit EventViewModelBase<string>() instead of MainWindowEvents, using a string as the command parameter will work, though.

[ruxo]

Just post here for reference: http://stackoverflow.com/questions/335849/wpf-commandparameter-is-null-first-time-canexecute-is-called

So the true culprit is setting CommandParameter does not re-evaluate CanExecute method. Simple workaround is just swap the order of Command and CommandParameter in the XAML.