Question

Given the following code, will the ReleaseCOMObj() method release the original COM object, or will it implicitly create a copy and release that?

private void TestRelease()
{
    Excel.Workbook workbook = excel.ActiveWorkbook;
    // do stuff
    ReleaseComObj(workbook);
}

private static void ReleaseComObj(Object obj)
{
    if (obj != null)
    {
        Marshal.ReleaseComObject(obj);
        obj = null;
    }
}

Update: Changed method to static. See Passing COM objects as parameters in C# for an explanation as to why the Object parameter cannot be ref Object obj.

Answer 1

C# parameters are passed by reference.

Therefore, it will release the original COM object, but it won’t set the original variable to null.

To set the original variable to null, change it to a ref parameter, which passes a variable by reference. (and call it with the ref keyword)

Also, by the way, the method should be static, since it doesn’t use this.