Get instance of Excel application with C# by Handle

Question

I have a c# simple application that have to write some values in a excel ranges of a specific worksheet. I create an instance of Excel application if not exist, but if exist i want to set active it and take an instance if it to use in my code.

I use this code to create a new application:

Microsoft.Office.Interop.Excel app = 
   new Microsoft.Office.Interop.Excel.Application();
app.Visible = true;

To get the handle of active excel window i use this api

[DllImportAttribute("User32.dll")]
private static extern int FindWindow(String ClassName, String WindowName);

How can i get an instance of excel application by an handle?

int hWnd = FindWindow(null, "Microsoft Excel - MySheet.xlsx");
Microsoft.Office.Interop.Excel app = ....(hWnd)

Answer 1

Use the following code to get the first running instance of Excel:

oExcelApp =  (Excel.Application)System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application");

Example

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

    return instance;
}