How To Get an ArcGIS Add-in Dockable Window

It wasn't as easy as it first appeared. Here is a quote from an ESRI staff member that replied to my plea for help in the forums:

DockableWindow is a bit tricky here since it is implemented by two classes - 1) the UI part is the designer surface derived from controls and 2) the non-UI part is the class actually inherits from DockableWindow base class. 

FromID can only handle types derived from base classes declared in ESRI.ArcGIS.Desktop.AddIns.dll. You have to pass in the type that inherits DockableWindow, which is the inner class of the designer window itself if you are using the Add-in Wizard.

If you go to the xml declaration of the dockable window, you will see the class attribute is set to “DockableWindow1+AddinImpl”. You have to pass this type to get the dockablewindow implementation class first, then you have to expose a property there get a hold of the UI window.

While I won't pretend to understand stand it perfectly yet, I did come up with a solution that works well.

First, I added added a property called "UI" to the innerclass "AddinImpl" within my dockable window class that points to the dockable window class (why isn't this part of the template?):

/// <summary>
/// Implementation class of the dockable window add-in. It is responsible for 
/// creating and disposing the user interface class of the dockable window.
/// </summary>
public class AddinImpl : ESRI.ArcGIS.Desktop.AddIns.DockableWindow
{
    private DockableWindow1 m_windowUI;

    // this property is what I added - the rest was generated by the template
    internal DockableWindow1 UI
    {
        get { return m_windowUI; }
    }

    public AddinImpl()
    {
    }

    protected override IntPtr OnCreateChild()
    {
        m_windowUI = new DockableWindow1(this.Hook);
        return m_windowUI.Handle;
    }

    protected override void Dispose(bool disposing)
    {
        if (m_windowUI != null)
            m_windowUI.Dispose(disposing);

        base.Dispose(disposing);
    }
}

Then to get the dockable window from another class it was just a few lines:

// get reference to dockable window
DockableWindow1.AddinImpl winImpl = AddIn.FromID<DockableWindow1.AddinImpl>(ThisAddIn.IDs.DockableWindow1);
DockableWindow1 dockWin = winImpl.UI;

// or you could just do this
DockableWindow1 dockWin = AddIn.FromID<DockableWindow1.AddinImpl>(ThisAddIn.IDs.DockableWindow1).UI;

I spent hours trying to figure this out. Hopefully this will save you the head-ache. Anyone else out there using Add-ins yet?