如何使用带有MVVM和WPF的WF4将ViewModel传递给CodeActivity

Question

I am trying to integrate my current WPF/MVVM application to Workflow Foundation 4.0.

Currently one of my ViewModel methods is invoking my sample CodeActivity sending it some parameters.

Inside of my CodeActivity execute method I need to call some methods from the calling ViewModel. I would like to know what the best approach is to do this. So far I have identified three possible ways:

1. Send my ViewModel instance as an input argument to my CodeActivity
2. Send my ViewModel instance through a Constructor in my CodeActivity like public MyCodeActivity(ViewModel vm)
3. Wrap my CodeActivity in a WorkflowApplication and send my ViewModel instance as an extension using SynchronizationContext

So far I have tested options 2 and 3 and they work well apparently.

What is the optimal way to do this to avoid any issues like thread synchronization problems or other?

Thanks in advance,

Edit: Just to mention a possible scenario: If user picks value 'X' from a given dropdown list in my View I need to add object childA and childB to an ObservableCollection contained by a ParentObject exposed through a public property in my ViewModel. The logic to create the child objects and add them to the parent are in my ViewModel. But I want Workflow to contain the Business Rule itself.

Answer 1

Why does your CodeActivity need to know anything about a specific view model? I would look for another solution that allows your activity to maintain as much independence as possible. Two options I can think of off the top of my head:

1. Use an abstract class or interface so that your activity is not bound to a single viewmodel, ie, InArgument<IViewModel>
2. Facilitate communication using an event aggregation pattern (if possible if WF4, not too sure on this yet?), ie, give the activity what it needs to do it's job and let your view model listen for an event to receive updates from the activity

Without knowing the specifics of your application, I don't know which option would work best (or work at all), but I would avoid a direct connection between a given view model and a given CodeActivity .