COMAddIn.Object is always Null - outlook

Question

I am trying to implement a email functionality using VSTO Outlook AddIn. But
I am getting ComAddIn.Object as always null due to this i am not able to
access the member of VSTO AddIns
Outlook.Application OutlookObj = new Outlook.Application();
object AddinName = "OutlookAddIn";
COMAddIn AddIn = OutlookObj.COMAddIns.Item(ref AddinName);
IOutLookApp utils = (IOutLookApp)AddIn.Object;
utils.CallOlMethod();
This is TheAddIn.cs
namespace OutlookAddIn
{
public interface IOutLookApp
{
void CallOlMethod();
}
public partial class ThisAddIn
{
protected override object RequestComAddInAutomationService()
{
OutlookApp ol = new OutlookApp();
return ol;
}
#region VSTO generated code
private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
}
private void ThisAddIn_Shutdown(object sender, System.EventArgs e)
{
// Note: Outlook no longer raises this event. If you have code that
// must run when Outlook shuts down, see
https://go.microsoft.com/fwlink/?LinkId=506785
}
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InternalStartup()
{
this.Startup += new System.EventHandler(ThisAddIn_Startup);
this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown);
}
#endregion
public void CreateOutlookItem()
{
Outlook.MailItem newEmail = new Outlook.MailItem
{
To = "example#gmail.com",
Subject = "testing",
Importance = Outlook.OlImportance.olImportanceLow
};
newEmail.Send();
}
}
public class OutlookApp:
StandardOleMarshalObject,
IOutLookApp
{
public void CallOlMethod()
{
Globals.ThisAddIn.CreateOutlookItem();
}
}
}
What I am doing wrong here? though my AddIn class is exposed still the ComAddIn.Object is null, why? Kindly help resolving the issue.

Answer 1

To expose your VSTO add-in to external callers do following steps:
Define interface as dual and make it COM visible
[ComVisible(true)]
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
public interface IOutLookApp
{
void CallOlMethod();
}
Also define a class that implements the interface as shown bellow
[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
public class OutlookApp : StandardOleMarshalObject, IOutLookApp
{
public void CallOlMethod()
{
//do something
}
}
Read more: Call code in VSTO Add-ins from other Office solutions and
VSTO Add-ins, COMAddIns and RequestComAddInAutomationService
Edit:
It is also required to check "Register For Com interop" in project settings and make sure to run Visual Studio as administrator.