arcobjects 10.3.1 c#: Loading Addins programmatically

Question

I am writing addins in C#, and am trying to load an addin. I thought i had the solution, but it seems like the full code is not loaded.

The button is added to my toolbar, and code seems to run, too a point. Once i need to use the singleton extension of the child, it crashes.

The child addin will run by itself, with no issues.

Calling Addin (Parent):

public class ParentExten : Extension
{
 .....

/// <summary>
        ///
        /// </summary>
        protected override void OnStartup()
        {
            WireDocumentEvents();            
            // load other extensions:

            // Call FindExtension to load this just-in-time extension.  
            var ais =  ArcMap.Application.FindExtensionByName("ChildExtension");

        }

}

Child Addin: config.esriaddinx

<AddIn language="CLR4.5" library="name.dll" namespace="name">
    <ArcMap>
      <Extensions>
        <Extension id="childExtension" class="classname"  showInExtensionDialog="true" autoLoad="false" />
      </Extensions>
      <Commands >
        <Button  id="button_id" class="namspace.classname"  
                  image="Images\Layer.jpeg"  onDemand="true"/>

        <Tool id="tool_id" class="hiddenname" 
             category="Layer" image="Images\Layer.jpeg" onDemand="true" />
      </Commands>
    </ArcMap>
  </AddIn>

Answer 1

I came up with this solution by looking up the IExtensionManager/IExtensionConfig. The 'Child' extension is set to showInExtensionDialog="false" autoLoad="false"

Parent Extension: (called after IDocumentEvents_OpenDocumentEventHandler)

private bool LoadChildExtensions()
{          
   var child = ArcMap.Application.FindExtensionByName("ChildLayeExtension");
   var configext = child as IExtensionConfig;


   if(configext.State != esriExtensionState.esriESUnavailable)
   {
     configext.State = (configext.State == esriExtensionState.esriESEnabled) ? esriExtensionState.esriESDisabled : esriExtensionState.esriESEnabled;
   }
   else
   {
      ReportError(true, string.Format("ChildLayeExtension is {0}", configext.State.ToString()));
   }

   child.Startup(ArcMap.ThisApplication);
   return true;
 }