Have processing icons appear during custom button action - acumatica

Question

I have a process which is activated by a button on a screen - but I'd like to know how to make it work like a process button, where the spinning wheel happens and the green checkbox appears at the end. I've got the following code, which I had wrapped in a PXLongOperation.StartOperation(...) as follows (the PXLongOperation is commented out here, because it didn't seem to be doing anything):
public PXAction<APInvoice> CreatePOBillings;
// [PXButton(CommitChanges = true)]
[PXProcessButton]
[PXUIField(DisplayName = "Create PO Billings", MapEnableRights = PXCacheRights.Update, MapViewRights = PXCacheRights.Update)]
protected void createPOBillings()
{
int i = 0;
try
{
//This wraps the whole process into a 'PXLongOperation' function that will create the spinning 'busy' wheel at the top toolbar...
//PXLongOperation.StartOperation(this, delegate()
//{
var apinvoice = (APInvoice)Base.Document.Current;
if (apinvoice == null) return;
string RefNbr = apinvoice.RefNbr;
//Run the stored procedure which will get the records to create the Project Transactions. This will populate the table 'xCreatePOBilings':
var pars = new PXSPParameter[] { new PXSPInParameter("#p_RefNbr", RefNbr) }; //, new PXSPOutParameter("p2", outp2) };
var results = PXDatabase.Execute("xspMarketingPOBilling", pars);
//Get the dataset from the xCreatePOBillings table which was populated from the stored procedure above:
PXResultset<xCreatePOBillings> res = PXSelect<xCreatePOBillings,
Where<xCreatePOBillings.ponbr, Equal<Required<xCreatePOBillings.ponbr>>>
,OrderBy<Asc<xCreatePOBillings.ponbr
,Asc<xCreatePOBillings.destProject
,Asc<xCreatePOBillings.startDate>>>>>.Select(Base, RefNbr);
//Create the graph for the Project Transactions screen:
RegisterEntry graph = PXGraph.CreateInstance<RegisterEntry>();
//Create a new cache object for the header of Project Transactions:
PMRegister pmreg = new PMRegister();
pmreg.Module = "PM";
graph.Document.Insert(pmreg);
//Define the cache for the Project Transactions screen's grid records:
PMTran pmtrn;
foreach (PXResult<xCreatePOBillings> rec in res)
{
....
graph.Actions.PressSave();
//});
What is the best way to achieve this, if it's possible?

Answer 1

When the static PXLongOperation.StartOperation method is invoked inside a BLC extension class, as first parameter it can only accept Base property instead of this keyword:
PXLongOperation.StartOperation(Base, delegate()
{
...
}