Windows Workflow Custom Sequence Activity

Question

I'm working with Windows Workflow 4, and I need to create a C# activity that, basically, inherits from the Sequence activity. I want it to look just like the Sequence activity, so a user can drag and drop other activities onto it from the designer. But, it acts differently in the code (maybe I want to run them in a different order, or do special actions between each one, it shouldn't matter).

How can I do this? I see a similar question was asked about this, and only one person responded with a suggestion that only applies to Windows Workflow 3. In version 4, a sequence activity can't be inherited from, to say the least.

This doesn't seem like a very far fetched concept. A Sequence activity is provided as a built in activity. So, it seems logical that it should be reproducible, or at least inheritable, so I can have a customized version of a Sequence activity.

Anyone have any ideas?

I ganked my version from MSDN: social.msdn.microsoft.com/Forums/ar-SA/wfprerelease/thread/… required some modification and some reflection work to get everything working, but it looks as expected. — user1228
Will: that looks great, and this should be an answer. But I am not sure how to implement it. There's the "SpacerTemplate" UserControl, and when I paste this code into VS2010, it has several errors. The class derives from IComponentConnector, but doesn't implement either of its methods. And if I implement them with NotImplementedException() stubs, I get more errors: "this.dropTarget" doesn't exist, for instance. And the activity designer code (sap:WorkflowItemsPresenter), well, I can't figure out where to put that. I'm new to workflows so I could really use a more idiot proof example. — Jay Sullivan
Ooo! Ooo! Okay, I had to change the namespace in the SpacerTemplate XAML to match the Code's namespace. Duh! That fixes the interface implementation issue (well, it compiles). Now I gotta figure out how to create that designer. I don't know where to put that sap:WorkflowItemsPresenter block of XAML. — Jay Sullivan
Your IComponentConnector issue is caused by copypasting code from the internets. This is a programming sin, and you must repent by NOT copypasting codes but by creating a new UserControl and using the example code as a GUIDE. Your issues have nothing to do with WF, they are all WPF. Slow down and understand what you are doing before doing it. — user1228
That's usually a problem with the binding. Start small, then go big. — user1228

Jay Sullivan Jay Sullivan · Accepted Answer · 2011-09-29T15:14:49

The "System.Activities.Core.Presentation.SequenceDesigner" designer is already available in WF 4. One can then compose a Sequence activity and use this designer for the outer class.

Here's a working example:

using System.Activities;
using System.Activities.Statements;
using System.Collections.ObjectModel;
using System.ComponentModel;

[Designer("System.Activities.Core.Presentation.SequenceDesigner, System.Activities.Core.Presentation")]
public class MySeq : NativeActivity
{
    private Sequence innerSequence = new Sequence();

    [Browsable(false)]
    public Collection<Activity> Activities
    {
        get
        {
            return innerSequence.Activities;
        }
    }

    [Browsable(false)]
    public Collection<Variable> Variables
    {
        get
        {
            return innerSequence.Variables;
        }
    }

    protected override void CacheMetadata(NativeActivityMetadata metadata)
    {
        metadata.AddImplementationChild(innerSequence);
    }

    protected override void Execute(NativeActivityContext context)
    {
        context.ScheduleActivity(innerSequence);
    }

}

This is forwarding the real behavior on to a private innerSequence, which might make this code seem useless, but note that in the Execute method it gives us a chance to do things before and after execution. If we want to provide customized behavior, we'd have to implement it instead of forwarding to an inner private activity.

Windows Workflow Custom Sequence Activity

1 Answers