title: Google Script - Can't combine on the same script multiple selection from listBox and SubmitButton
body: <p>I'm trying to code on google app and I've encountered one issue. For example, let's consider this example code on google website ( link's here <a href="https://developers.google.com/apps-script/class_formpanel" rel="nofollow">https://developers.google.com/apps-script/class_formpanel</a> )</p>
  
  <pre><code> function doGet() {
   var app = UiApp.createApplication();
   var form = app.createFormPanel();
   var flow = app.createFlowPanel();
   flow.add(app.createTextBox().setName("textBox"));
   flow.add(app.createListBox().setName("listBox").addItem("option 1").addItem("option 2"));
   flow.add(app.createSubmitButton("Submit"));
   form.add(flow);
   app.add(form);
   return app;
   }
  
   function doPost(eventInfo) {
   var app = UiApp.getActiveApplication();
   app.add(app.createLabel("Form submitted. The text box's value was '" +
     eventInfo.parameter.textBox +
     "' and the list box's value was '" +
     eventInfo.parameter.listBox + "'"));
   return app;
    }
  </code></pre>
  
  <p>My issue is that I want to select multiple values on the listbox. I change then line 6 in</p>
  
  <pre><code> flow.add(app.createListBox(true).setName("listBox").addItem("option 1").addItem("option 2"));
  </code></pre>
  
  <p>to allow multiple selection. But the result is that only the last selected value is taken, preventing multiple selections. Apparently, it is due to the submitButton. I need to keep the formPanel because on a further code I'll like to combine uploading files and listBox multiple selection. How may I fix that? Thank you a lot </p>