Setting internal properties in composite WF4 Activities at design time - wcf

Question

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?

Answer 1

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;
metadata.AddImplementationChild(_receive);
metadata.AddImplementationChild(_sendReply);
_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;
base.CacheMetadata(metadata);
}
protected override void Execute(NativeActivityContext context)
{
context.ScheduleActivity(_receive, ReceiveCompleted);
}
private void ReceiveCompleted(NativeActivityContext context, ActivityInstance completedInstance)
{
context.ScheduleActivity(_sendReply);
}
}