How to get output value (customOut) from EnvDTE Commands.Raise method? - visual-studio

Question

I am writing a Visual Studio 2012 add-in that needs to send a command to the built-in T-SQL Editor. The command in question, sqlEditorSqlDatabaseCommand, can be used to either set or get the name of the current database in the editor. Here is some (working) code that sets the database name:
const string guidSqlEditorCommandSet = "b371c497-6d81-4b13-9db8-8e3e6abad0c3";
const int sqlEditorSqlDatabaseCommand = 0x312;
object customIn = "myDatabaseName";
object customOut = null;
m_applicationObject.Commands.Raise(guidSqlEditorCommandSet, sqlEditorSqlDatabaseCommand, ref customIn, ref customOut);
The problem is, I need to get the current database name, which would require use of the customOut parameter, and I can't figure out how to make customOut work.
The implementation of sqlEditorSqlDatabaseCommand is as follows (via Reflector):
protected override int HandleExec(uint nCmdexecopt, IntPtr pvaIn, IntPtr pvaOut)
{
AuxiliaryDocData auxiliaryDocDataForEditor = base.GetAuxiliaryDocDataForEditor();
if (auxiliaryDocDataForEditor != null)
{
QueryExecutor queryExecutor = auxiliaryDocDataForEditor.QueryExecutor;
if (queryExecutor != null)
{
if (pvaIn != IntPtr.Zero)
{
string objectForNativeVariant = (string) Marshal.GetObjectForNativeVariant(pvaIn);
this.SetDatabase(auxiliaryDocDataForEditor, objectForNativeVariant);
}
else if (pvaOut != IntPtr.Zero)
{
object database = string.Empty;
IDbConnection connection = queryExecutor.ConnectionStrategy.Connection;
if (((connection != null) && (connection.State == ConnectionState.Open)) && !string.IsNullOrEmpty(connection.Database))
{
database = connection.Database;
}
else
{
database = string.Empty;
}
Marshal.GetNativeVariantForObject(database, pvaOut);
}
}
}
return 0;
}
According to every marshaling example I've seen, I should be able to pass null for both customIn and customOut, and the database name should be placed in customOut. When I do this, I get an E_INVALIDARG exception from Commands.Raise:
System.ArgumentException: The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG))
at EnvDTE.Commands.Raise(String Guid, Int32 ID, Object& CustomIn, Object& CustomOut)
at RDSVisualStudioAddIn.Exec(String commandName, vsCommandExecOption executeOption, Object& varIn, Object& varOut, Boolean& handled) in c:\RDS\RDSVisualStudioAddIn\Connect.cs:line 193
Has anyone used Commands.Raise with the customOut parameter?