The signature for the Office 2010 backstage OnShow callback looks like so:

void Backstage_OnShow(object contextObject)

But I cannot find anywhere that documents what the contextObject is.

Well I can tell you – it’s the Window object that is hosting the backstage as shown. I’m guessing it’s an object because it will be the equivalent Window object in whichever Office application happens to be running.

I just stumbled on an undocumented feature of the getImage callback for the Office 2010 Ribbon (well, backstage actually)

The “official” callback signature is

Public System.Drawing.Bitmap GetImage(Office.IRibbonControl control) {}

Or sometimes

Public stdole.IPictureDisp GetImage(Office.IRibbonControl control) {}

I don’t know which is “best”, but if you return a Bitmap it sure is easier to work with.

Now back in Office 2007 there are a couple controls with a GetImageMso callback that allows you to provide an Office Control ID for a built-in image. This is lacking from any 2010 backstage controls.

Whilst doing some unpleasant native debugging to try to “figure out” what office expects in these callback delegates, I tried creating a GetImage callback that returned a string.

<?xml version="1.0" encoding="utf-8"?>
<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui" onLoad="Ribbon_Load">
  <backstage>
    <tab id="MyTabShare" label="Testing">
      <firstColumn>
        <group id="MyGroup">
          <topItems>
            <imageControl id="imageControl1" getImage="GetImage"/>
          </topItems>
        </group>
      </firstColumn>
    </tab>
  </backstage>
</customUI>

        public string GetImage(Office.IRibbonControl control)
        {
            return "hello world";
        }

I was really hoping for an error about a bad callback signature, possible including an exception in MSO.DLL that I could dig into…

Instead, I got this:

Really… So when GetImage returns a string, Office interprets it as an ImageMso? I had to try:

        public string GetImage(Office.IRibbonControl control)
        {
            return "WindowKeepOnTop";
        }

The result: SUCCESS!

So, at least for the Office 2010 backstage ribbon, the getImage callback has an alternate signature:

string GetImage(IRibbonControl control)

Where string is an Office Image Id (or the value you would place statically in imageMso).