The current topic describes, how you can use other applications, like Microsoft Excel in your EPLAN API add-in. 

If you want to access data of an other program, the application needs to have a suitable interface. Because an EPLAN add-in is written in managed code (C# or VB.Net), you need to be able to set a reference to the other program. Either the other application already exposes its interface as .Net assembly, or the .Net framework creates an interop assembly from a COM type library. 

The following example shows the use of Microsoft Excel 2003. Excel exposes its functions as COM interface. In your EPLAN add-in, you can add a Reference to the registered type library of Excel: 

After you added the reference, the development environment creates an interop assembly. The types of this assembly then can be used in managed code (C# etc.): 

In your application code, the use of Excel would look like in the following example: 

Excel.ApplicationClass oExcel= new Excel.ApplicationClass();
oExcel.Visible=true;
new Decider().Decide(EnumDecisionType.eOkDecision, "Now Excel should be visible!" ,"", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
Excel.Workbooks iWorkBooks=oExcel.Workbooks;
Excel.Workbook  iWorkBook= iWorkBooks.Add(Excel.XlWBATemplate.xlWBATWorksheet);
Excel.Worksheet iSheet = (Excel.Worksheet)oExcel.ActiveSheet;
new Decider().Decide(EnumDecisionType.eOkDecision, "All project messages are now written into an Excel worksheet!", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
Check oCheck = new Check();
oCheck.VerifyProject(oProject);
PrjMessagesCollection colPrjMsg = new PrjMessagesCollection(oProject);
PrjMessagesEnumerator itPrjMsg = colPrjMsg.GetPrjMsgEnumerator();
itPrjMsg.MoveNext();
int nNr=1;
do
{
   ProjectMessage oPrjMsg = itPrjMsg.Current as ProjectMessage;
   if (oPrjMsg != null)
   {
       nNr++;
       iSheet.Cells[nNr, 1] = oPrjMsg.GetGroup().ToString() + GetId().ToString();
       iSheet.Cells[nNr, 2] = oPrjMsg.GetText();
   }
} while(itPrjMsg.MoveNext());

new Decider().Decide(EnumDecisionType.eOkDecision, "Action completed!", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
oExcel.Quit();

Dim oExcel As New Excel.ApplicationClass()
oExcel.Visible = True
Dim dec As Decider = New Decider
dec.Decide(EnumDecisionType.eOkDecision, "Now Excel should be visible!", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK)
Dim iWorkBooks As Excel.Workbooks = oExcel.Workbooks
Dim iWorkBook As Excel.Workbook = iWorkBooks.Add(Excel.XlWBATemplate.xlWBATWorksheet)
Dim iSheet As Excel.Worksheet = CType(oExcel.ActiveSheet, Excel.Worksheet)
dec.Decide(EnumDecisionType.eOkDecision, "All project messages are now written into an Excel worksheet!", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK)
Dim oCheck As New Check()
oCheck.VerifyProject(oProject)
Dim colPrjMsg As New PrjMessagesCollection(oProject)
Dim itPrjMsg As PrjMessagesEnumerator = colPrjMsg.GetPrjMsgEnumerator()
itPrjMsg.MoveNext()
Dim nNr As Integer = 1
Do
   Dim oPrjMsg As ProjectMessage = itPrjMsg.Current
   If Not (oPrjMsg Is Nothing) Then
      nNr += 1
      iSheet.Cells(nNr, 1) = oPrjMsg.GetGroup().ToString() + GetId().ToString()
      iSheet.Cells(nNr, 2) = oPrjMsg.GetText()
   End If
Loop While itPrjMsg.MoveNext()
dec.Decide(EnumDecisionType.eOkDecision, "Action completed!", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK)
oExcel.Quit()

Excel is started as a separate process. The only object, you create with new is Excel.ApplicationClass. All other objects like Excel.Workbook, are created -- or queried from Excel -- through functions of the Application object. 

Each call of Excel functions is a communication between processes!