Form DataSource Deleting EventHandler

i wanna prevent the user from delete a record based on condition

i used eventhandler for form datasource deleting eventhandler i used the below code

[FormDataSourceEventHandler(formDataSourceStr(PurchTable, PurchTable), FormDataSourceEventType::Deleting)]
public static void PurchTable_OnDeleting(FormDataSource sender, FormDataSourceEventArgs e)
{
// ValidateEventArgs args = e as ValidateEventArgs;
//boolean result = args.parmValidateResult();

PurchTable purchTable = sender.cursor() ;

if(purchTable.purchid == '1234')
checkFailed("you can not delete this PO");


}
but still can deleted it
i tried to get the eventargs result by below code

// ValidateEventArgs args = e as ValidateEventArgs;
//boolean result = args.parmValidateResult();

but it gives and error i wanted to do like that

// ValidateEventArgs args = e as ValidateEventArgs;
//boolean result = args.parmValidateResult()

if(purchTable.purchid == '1234')
result = result  && checkFailed("you can not delete this PO");

but it gives an error

any help please?