VBA focus passing - excel

Question

trying to do in another focus with the window from the workbook from first trying to do in another focus with the window from the workbook from first
Sub Update_DHL()
Workbooks.Open Filename:=trk
Workbooks.Open Filename:=stp
Workbooks.Open Filename:=dhl
Windows(stp).Activate
Workbooks(stpfile).Activate
Range("B2").Select
ActiveCell.Formula = _
"Hi"
Range(Cells(2, 2), Cells(2, 2)).Copy
'Range(Cells(3, 2), Cells(65536, 45)).Select
'Selection.ClearContents
'Range(Cells(3, 47), Cells(65536, 74)).Select
'Selection.ClearContents
' Set wb = Workbooks("VMW Macro.xlsm") 'Name of the workbook you are copying from
' Set ws = wb.Sheets("Extract") 'Name of sheet you are copying
' DateStamp = Format(Now(), "mm-dd-yyyy hhmmss")
End Sub

Answer 1

Make sure you define variables for your workbooks and worksheets properly. You can then use them for your Range and Cells objects to specify in which workbook and worksheet they are. This way you don't need .Activate or .Select because the code even works if the workbook has no focus.
Make sure in your entire code there is no Range and Cells object without a workbook and worksheet specified. Either by using a variable like shown below. Or directly like ThisWorkbook.Worksheets("Sheet1").Range(…).
You only need to .Activate or .Select if you want to focus it for the user. You never need to do this to make VBA work properly (VBA can work with non-focused workbooks/worksheets).
Option Explicit
Sub Update_DHL()
'open your workbooks
On Error GoTo ERR_WB_OPEN
Dim wbTrk As Workbook
Set wbTrk = Workbooks.Open(Filename:=[truckfilePath])
Dim wbStp As Workbook
Set wbStp = Workbooks.Open(Filename:=[stopfilePath])
Dim wbDhl As Workbook
Set wbDhl = Workbooks.Open(Filename:=[dhlfilePath])
On Error GoTo 0
'define in which worksheet in those workbooks you want to work
Dim wsTrk As Worksheet
Set wsTrk = wbTrk.Worksheets("SheetName")
Dim wsStp As Worksheet
Set wsStp = wsStp.Worksheets("SheetName")
Dim wsDhl As Worksheet
Set wsDhl = wsDhl.Worksheets("SheetName")
'now work with those worksheets directly (no activate or select needed!)
wsStp.Range("B2").Formula = "=IF(SUMIF('Route Master.xls'!$C$7:$C$65536,$A2,'Route Master.xls'!$Q$7:$Q$65536)>0,TRUE,FALSE)"
wsStp.Range("B2").Copy
wsStp.Range(wsStp.Cells(2, 2), wsStp.Cells(EndRow2, 2)).PasteSpecial Paste:=xlPasteFormulas, Operation:=xlNone, SkipBlanks:=False, Transpose:=False
' note this code does not work because `EndRow2` is nod defined
'select and activate a specific workbook/worksheet
'you do this ONLY if you want to focus it for the USER. Never do this for VBA instead work directly with the worksheets as shown above.
wbDhl.Activate
wsDhl.Select
Exit Sub
ERR_WB_OPEN:
MsgBox "One of the files could not be loaded.", vbCritical
End Sub
Don't forget to close your workbooks wbDhl.Close SaveChanges:=True/False otherwise they stay open.

Answer 2

See below. You can reference the workbook directly as pointed out by BigBen. In code, you never need to select ranges or activate workbooks/worksheets. You just need to reference them directly.
Notice I also added explicit declaration of types.
Dim a, b As Long
The line above will declare a as a variant and b as long
Sub Update_DHL()
Dim trk As Workbook, stp As Workbook, dhl As Workbook, wb As Workbook, wbNew As Workbook
Dim ws As Worksheet
Dim stpfile As String, DateStamp As String, strFolderpath As String
Dim EndRowTrk As Long, EndRowStp As Long, EndRowDHL As Long
Dim fileExplorer As FileDialog
Set dhl = [dhlfilePath]
Set trk = [truckfilePath]
Set stp = [stopfilePath]
stpfile = stp
Workbooks.Open Filename:=trk
Workbooks.Open Filename:=stp
Workbooks.Open Filename:=dhl
With Workbooks(stpfile).Worksheets(1)
.Range("B2").Formula = "Hi"
End With
End Sub