excel - No definition found for GetActiveObject from System.Runtime.InteropServices.Marshal C#

Question

I'm trying to connect to a running Excel instance, but when I try to use the following code snippet:

using Microsoft.Office.Interop.Excel;
using System.Runtime.InteropServices;

public Application StartExcel()
{
    Application instance = null;
    try
    {
        instance = (Application)Marshal.GetActiveObject("Excel.Application");
    }
    catch (COMException ex)
    {
        instance = new ApplicationClass();
    }

    return instance;
}

I found similar snippets on the internet, but when I compile this code I get the following error:

error CS0117: 'Marshal' does not contain a definition for 'GetActiveObject'.

I do not know why, because I have the following NuGet packages: - Microsoft.Office.Interop.Excel - System.Runtime.InteropServices

Answer 1

We need to pull the GetActiveObject(String ProgID) function from the source code GitHub.Microsoft

Create your own class, for example - Marshal2

And use as before

Marshal2.GetActiveObject(progID);

Source code

public static class Marshal2
{
    internal const String OLEAUT32 = "oleaut32.dll";
    internal const String OLE32 = "ole32.dll";

    [System.Security.SecurityCritical]  // auto-generated_required
    public static Object GetActiveObject(String progID)
    {
        Object obj = null;
        Guid clsid;

        // Call CLSIDFromProgIDEx first then fall back on CLSIDFromProgID if
        // CLSIDFromProgIDEx doesn't exist.
        try
        {
            CLSIDFromProgIDEx(progID, out clsid);
        }
        //            catch
        catch (Exception)
        {
            CLSIDFromProgID(progID, out clsid);
        }

        GetActiveObject(ref clsid, IntPtr.Zero, out obj);
        return obj;
    }

    //[DllImport(Microsoft.Win32.Win32Native.OLE32, PreserveSig = false)]
    [DllImport(OLE32, PreserveSig = false)]
    [ResourceExposure(ResourceScope.None)]
    [SuppressUnmanagedCodeSecurity]
    [System.Security.SecurityCritical]  // auto-generated
    private static extern void CLSIDFromProgIDEx([MarshalAs(UnmanagedType.LPWStr)] String progId, out Guid clsid);

    //[DllImport(Microsoft.Win32.Win32Native.OLE32, PreserveSig = false)]
    [DllImport(OLE32, PreserveSig = false)]
    [ResourceExposure(ResourceScope.None)]
    [SuppressUnmanagedCodeSecurity]
    [System.Security.SecurityCritical]  // auto-generated
    private static extern void CLSIDFromProgID([MarshalAs(UnmanagedType.LPWStr)] String progId, out Guid clsid);

    //[DllImport(Microsoft.Win32.Win32Native.OLEAUT32, PreserveSig = false)]
    [DllImport(OLEAUT32, PreserveSig = false)]
    [ResourceExposure(ResourceScope.None)]
    [SuppressUnmanagedCodeSecurity]
    [System.Security.SecurityCritical]  // auto-generated
    private static extern void GetActiveObject(ref Guid rclsid, IntPtr reserved, [MarshalAs(UnmanagedType.Interface)] out Object ppunk);

}