Setting internal properties in composite WF4 Activities at design time

I want to create a composite Windows Workflow Activity (under .NET 4) that contains a predefined ReceiveAndSendReply Activity. Some of the properties are predefined, but others (particularly ServiceContractName) need to be set in the designer.

I could implement this as an Activity Template (the same way ReceiveAndSendReply is implemented), but would rather not. If I later change the template, I'd have to update all previously created workflows manually. A template would also permit other developers to change properties that should be fixed.

Is there a way to do this from a Xaml Activity? I have not found a way to assign an Argument value to a property of an embedded Activity. If not, what technique would you suggest?


I haven't done this using a composite XAML activity and am getting some errors when I try but doing so through a NativeActivity is no problem. See the example code below.

public class MyReceiveAndSendReply : NativeActivity
    private Receive _receive;
    private SendReply _sendReply;

    public string ServiceContractName { get; set; }
    public string OperationName { get; set; }

    protected override bool CanInduceIdle
        get { return true; }

    protected override void CacheMetadata(NativeActivityMetadata metadata)
        _receive = _receive ?? new Receive();
        _sendReply = _sendReply ?? new SendReply();
        _receive.CanCreateInstance = true;

        _receive.ServiceContractName = ServiceContractName;
        _receive.OperationName = OperationName;

        var args = new ReceiveParametersContent();
        args.Parameters["firstName"] = new OutArgument<string>();
        _receive.Content = args;

        _sendReply.Request = _receive;

        var results = new SendParametersContent();
        results.Parameters["greeting"] = new InArgument<string>("Hello there");
        _sendReply.Content = results;


    protected override void Execute(NativeActivityContext context)
        context.ScheduleActivity(_receive, ReceiveCompleted);


    private void ReceiveCompleted(NativeActivityContext context, ActivityInstance completedInstance)

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