How to select next workflow activity using Core Service?

Question

I have a decision activity and using the core service I want to finish the current activity, assign the next person and the next activity. This is working fine for a manual activity where I only need to assign the person.

However, the decision activity also requires the next activity to perform and I don't know how to set it. Here is my error: "The next Workflow Activity has not been selected." Any ideas?

Here is my code so far:

using (SessionAwareCoreServiceClient client = new SessionAwareCoreServiceClient(binding))
{
    // Get Component
    var wfItem = client.Read(componentUri, new ReadOptions()) as ComponentData;
    if (wfItem == null)
        return;

    // Get Workflow info for Component
    var activityUri = wfItem.WorkflowInfo.ActivityInstance.IdRef;
    var activityTitle = wfItem.WorkflowInfo.ActivityInstance.Title;

    // Set Finish Message
    ActivityFinishData finishData = new ActivityFinishData();
    finishData.Message = finishMessage;

    // Set Previous performer
    LinkToTrusteeData guiltyPerson = new LinkToTrusteeData();
    TridionHelper tridionHelper = new TridionHelper();
    guiltyPerson.IdRef = tridionHelper.GetPreviousAssigneeUri(componentUri, activityUri, activityTitle);
    finishData.NextAssignee = guiltyPerson;

    // Finish
    client.FinishActivity(activityUri, finishData, new ReadOptions());
}

Answer 1

Posting answer from Frank here for community users convenience.

You need to use DecisionActivityFinishData instead of of ActivityFinishData.

var decisionActivityFinishData = new DecisionActivityFinishData
{
  NextActivity = new LinkToActivityDefinitionData{IdRef = "next activity ID"}
};
csClient.FinishActivity(currentactivity.Id, decisionActivityFinishData, 
                        readoption);