Sharepoint App cannot start hostweb workflow

Question

I have a site workflow on my Apps hostweb that I would like to call from within the app.

The issue I am facing is that while I can successfully query the WorkflowServicesManager, find the specific workflow subscription and initiate a startWorkflow - I am getting a NullReferenceException within the ULS logs.

My suspicion is that this has something to do with the App context not sending the correct information to the WorkflowServicesManager

var ctx = new SP.ClientContext(appweburl);
var appContextSite = new SP.AppContextSite(ctx, hostweburl);
ctx.load(appContextSite.get_web());

var wfServiceManager = SP.WorkflowServices.WorkflowServicesManager.newObject(ctx, appContextSite.get_web());
var wfSubService = wfServiceManager.getWorkflowSubscriptionService();
var wfSubs = wfSubService.enumerateSubscriptions();
var wfParams = new Object();
wfParams['personName'] = "Thomas";
var wfSub = null;
ctx.executeQueryAsync(function () {

  wfSubEnum = wfSubs.getEnumerator();
  while (wfSubEnum.moveNext()){ if(wfSubEnum.get_current().get_name() == "PersonWorkflow"){} wfSub = wfSubEnum.get_current(); }

  wfServiceManager.getWorkflowInstanceService().startWorkflow(wfSub, wfParams );
  ctx.executeQueryAsync(function () {

  })

})

The same code (with just Client context) on the hostweb works fine. Using wireshark I can see that the App sending an extra contructor in the XML during POST - but I am still thinking this is something to do with the appweb contexts or maybe the User Profile Service/WorkFlow manager not handling the App "user".

A similar post here going into quite alot of depth but the resolution does seem to be what I have already been doing. I don't think I am doing anything wrong in that regard.

Is it possible to call a hostweb site workflow from within a sharepoint App?

Update.

It seems as though my problem was with enumerateSubscriptions() I wanted to enumerate them to get the workflow based on its name, but get_current() does not return an object that startWorkflow can use.

the following code now works

var ctx = new SP.ClientContext.get_current();
var hostCtx = new SP.AppContextSite(ctx, hostweburl);

var wfServiceManager = SP.WorkflowServices.WorkflowServicesManager.newObject(ctx, hostCtx.get_web());
var wfSubService = wfServiceManager.getWorkflowSubscriptionService();
var wfSubs = wfSubService.enumerateSubscriptions();
var wfSub = null;
var wfParams = new Object();
wfParams['personName'] = "thomas";

ctx.load(wfSubs);
ctx.executeQueryAsync(
  function () {
   var wfSubEnum = wfSubs.getEnumerator();
   while (wfSubEnum.moveNext()){ if(wfSubEnum.get_current().get_name() == "PersonWorkflow"){ wfSub = wfSubService.getSubscription(wfSubEnum.get_current().get_id()) }  };
   wfServiceManager.getWorkflowInstanceService().startWorkflow(wfSub, wfParams);
    ctx.executeQueryAsync(function() {});
  }
);

Answer 1

This is what I use to start workflows on the host web.

var startWorkflow = function(subId, itemId) {
    var d = $.Deferred(),
        ctx = new SP.ClientContext.get_current(),
        hostCtx = new SP.AppContextSite(ctx, this.hostUrl),
        wfServiceManager = SP.WorkflowServices.WorkflowServicesManager.newObject(ctx, hostCtx.get_web()),
        wfSubService = wfServiceManager.getWorkflowSubscriptionService();
    ctx.load(wfSubService);

    ctx.executeQueryAsync(function() {
        var wfSubscription = wfSubService.getSubscription(subId);
        wfServiceManager.getWorkflowInstanceService().startWorkflowOnListItem(wfSubscription, itemId, new Object());

        ctx.executeQueryAsync(function() {
            console.log("Workflow started.");
            d.resolve();
        }, function(sender, args) {
            console.error("Failed to start the workflow. " + args.get_message());
            d.reject();
        });
    }, function(sender, args) {
        console.error("Failed to start the workflow. " + args.get_message());
        d.reject();args.get_message());
    });
    return d.promise();
};

The key difference being I pass in the subscription id of the workflow I need to start.