VBA Switch from an open excel app to a different open Excel app

Question

I can have multiple Excel 2010 instances open at once because I'm using VBA Excel 2010. I have workbook1 open in the current Excel app, and I need to import data from workbook2 (which is open in a different Excel app). I've discovered that, even if workbook2 is open in another Excel app, APPACTIVATE will tell whether it is or is not. If not open right now, it's simple... Within the present Excel application, I simply open workbook 2, get my data, update workbook 1, and then dismiss workbook 2. So if workbook2 is already open, I have to access it, retrieve my information, update workbook1, and leave workbook2 alone. Can I access the workbook2 app in any way?

Sub AppAct()

    'Workbook (1): workbook.name="Book1"
    'Workbook (2): workbook.name="Fuel2010I.xlsm"
    'Workbook (2): workbook.fullname="C:\FltTools\Fuel2010I.xlsm"
    'Sheets("FL") exists in Workbook (2)
    'Sheets("S") exists in Workbook (1)
    
    On Error Resume Next
    AppActivate ("FUEL2010I.xlsm")
    If Err.Number > 0 Then 'if workbook not already open, then open it and select sheet "FL"
        On Error GoTo 0
        Workbooks.Open Filename:="C:\FltTools\Fuel2010I.xlsm"
        Sheets("FL").Select 'works fine
    Else 'if the workbook is open, select sheet "FL"
        On Error GoTo 0
        Sheets("FL").Select 'Subscript out of range, I'm not talking with FUEL2010I.xlsm
    End If
    Sheets("S").select
End Sub

I've tried the code as above. The code does not switch to the workbook2 instance of Excel

Answer 1

Switch Between Excel Instances Using AppActivate

• After app-activating, you need to activate the window as illustrated in the following code.

A Quick Fix

Sub AppAct()
    
    Dim ErrNumber As Long

    On Error Resume Next
        AppActivate "FUEL2010I.xlsm"
        ErrNumber = Err.Number
    On Error GoTo 0
    
    If ErrNumber > 0 Then ' workbook is not open in another instance
        Workbooks.Open Filename:="C:\FltTools\Fuel2010I.xlsm"
    Else ' workbook is open in another instance
        Windows("FUEL2010I.xlsm").Activate
    End If

    Sheets("FL").Select
    Sheets("S").Select

End Sub