Marshal.GetActiveObject(String) Method

Definition

Namespace:

System.Runtime.InteropServices

Assembly:

mscorlib.dll

Obtains a running instance of the specified object from the running object table (ROT).

public:
 static System::Object ^ GetActiveObject(System::String ^ progID);

[System.Security.SecurityCritical]
public static object GetActiveObject (string progID);

[<System.Security.SecurityCritical>]
static member GetActiveObject : string -> obj

Public Shared Function GetActiveObject (progID As String) As Object

Parameters

progID

String

The programmatic identifier (ProgID) of the object that was requested.

Returns

Object

The object that was requested; otherwise null. You can cast this object to any COM interface that it supports.

Attributes

SecurityCriticalAttribute

Exceptions

COMException

The object was not found.

Examples

The following example was run on a computer that was configured with a running instance of Microsoft Word. There were no instances of Microsoft Excel running.

The example calls GetActiveObject twice. The first call tries to retrieve a reference to an instance of Microsoft Word (an instance of the Word.Application object). The second call tries to retrieve a reference to an instance of Microsoft Excel (an instance of an Excel.Application object).

The code retrieves a reference to an instance of Microsoft Word successfully. However, because Microsoft Excel is not running, the attempt to retrieve the second object raises a COMException.

using System;
using System.Runtime.InteropServices;

class MainFunction
{
    static void Main()
        {
        Console.WriteLine("\nSample: C# System.Runtime.InteropServices.Marshal.GetActiveObject.cs\n"); 

        GetObj(1, "Word.Application");
        GetObj(2, "Excel.Application");
        }

    static void GetObj(int i, String progID)
    {
        Object obj = null;

        Console.WriteLine("\n" +i+") Object obj = GetActiveObject(\"" + progID + "\")");
        try
           { obj = Marshal.GetActiveObject(progID); }
        catch (Exception e)
           {
           Write2Console("\n   Failure: obj did not get initialized\n" + 
                         "   Exception = " +e.ToString().Substring(0,43), 0); 
           }
 
        if (obj != null)
           { Write2Console("\n   Success: obj = " + obj.ToString(), 1 ); }
    }

    static void Write2Console(String s, int color)
        {
        Console.ForegroundColor = color == 1? ConsoleColor.Green : ConsoleColor.Red;
        Console.WriteLine(s); 
        Console.ForegroundColor = ConsoleColor.Gray;
    }
}

/*
Expected Output:

Sample: C# System.Runtime.InteropServices.Marshal.GetActiveObject.cs

1) Object obj = GetActiveObject("Word.Application")

   Success: obj = System.__ComObject

2) Object obj = GetActiveObject("Excel.Application")

   Failure: obj did not get initialized
   Exception = System.Runtime.InteropServices.COMException
*/

Imports System.Runtime.InteropServices

Module Module1

    Sub Main()
        Console.WriteLine(vbcrlf + "Sample: VB System.Runtime.InteropServices.Marshal.GetActiveObject.vb" + vbcrlf) 
        GetObj(1, "Word.Application")
        GetObj(2, "Excel.Application")
    End Sub


    Sub GetObj(ByVal i As Integer, ByVal progID As [String])
        Dim obj As [Object] = Nothing
        
        Console.WriteLine((vbLf & i & ") Object obj = GetActiveObject(""") + progID & """)")
        Try
            obj = Marshal.GetActiveObject(progID)
        Catch e As Exception
            Write2Console((vbLf & "   Failure: obj did not get initialized" & vbLf & "   Exception = ") + e.ToString().Substring(0, 43), 0)
        End Try
        
        If obj IsNot Nothing Then
            Write2Console(vbLf & "   Success: obj = " & obj.ToString(), 1)
        End If
    End Sub

    Sub Write2Console(ByVal s As [String], ByVal color As Integer)
        Console.ForegroundColor = If(color = 1, ConsoleColor.Green, ConsoleColor.Red)
        Console.WriteLine(s)
        Console.ForegroundColor = ConsoleColor.Gray
    End Sub

End Module

'Expected Output:
'
'Sample: VB System.Runtime.InteropServices.Marshal.GetActiveObject.vb
'
'1) Object obj = GetActiveObject("Word.Application")
'
'   Success: obj = System.__ComObject
'
'2) Object obj = GetActiveObject("Excel.Application")
'
'   Failure: obj did not get initialized
'   Exception = System.Runtime.InteropServices.COMException
'

Remarks

GetActiveObject exposes the COM GetActiveObject function from OLEAUT32.DLL; however, the latter expects a class identifier (CLSID) instead of the programmatic identifier (ProgID) expected by this method. To obtain a running instance of a COM object without a registered ProgID, use platform invoke to define the COM GetActiveObject function. For a description of platform invoke, see Consuming Unmanaged DLL Functions.

ProgID and CLSID

Keys in the HKEY_CLASSES_ROOT subtree of the registry contain a variety of subkey types. Most of the subkeys are ProgIDs, which map a user-friendly string to a CLSID. Applications often use these human-readable strings instead of the numeric CLSIDs. Often, a component has a version-independent ProgID that is mapped to the latest version of the component that is installed on the system.

Applications and components primarily use ProgIDs to retrieve their corresponding CLSIDs.