deactivate the current sheet before going to another sheet - vba

Question

I am getting error while swapping with two sheets.
I open one sheet and paste some data in this,after that I call a function which opens another sheet.but when I again paste data in the first sheet it throws error.
For y = 1 To size
Set src = Workbooks.Open("C:Template\Mapping.xlsx")
Worksheets("Sheet1").Activate
Worksheets("Sheet1").Range("B" & rowCntr).Value = "abc"
newValue= getNewValue()
rowCntr=rowCntr+1
Next
public Function getNewValue()
Dim newV=123
Set src = Workbooks.Open("C:Template\Mapping - Development v1.0.xlsx")
getNewValue=newV
End Function
For the first time it works properly but after calling the function getNewValue() it throws error "Subscript out of range" at Worksheets("Sheet1").Range("B" & rowCntr).Value = "abc" line.
Please help.

Answer 1

Your code example is incomplete. Noteably, it doesn't define what src is, but that is exactly what the error is: I must assume that srcis a global variable and you set src in both your main function and in function getNewValue.
When getNewValue returns, src now points to another workbook in which your ranges don't exist.
Further I am not sure whether opening the workbook again and again results in it being reloaded, reset or that multiple copies will be opened. I suggest you open them only once, e.g.:
Dim src as Object
Dim src2 As Object
Function main (size As Integer)
Dim y As Integer
Dim rowCntr As Integer
Set src = Workbooks.Open("C:Template\Mapping.xlsx")
Set src2 = Workbooks.Open("C:Template\Mapping - Development v1.0.xlsx")
For y = 1 To size
src.Worksheets("Sheet1").Activate
src.Worksheets("Sheet1").Range("B" & rowCntr).Value = "abc"
newValue= getNewValue()
rowCntr=rowCntr+1
Next
End Function
Public Function getNewValue()
Dim newV
newV = 123
'...whatever you want to do...
getNewValue = newV
End Function

Answer 2

no need for selection/activation, use objects (workbook, range) reference instead, like follows
Set src = Workbooks.Open("C:Template\Mapping.xlsx") '<~~ open workbook outside the loop since it doesn't depend on it
For y = 1 To size
src.Worksheets("Sheet1").Range("B" & rowCntr).Value = "abc" '<~~ use "src" workbook reference to point to it whatever may be the currently active workbook
newValue= getNewValue()
rowCntr=rowCntr+1
Next