How to move NSD_OnBack function from the section in NSIS - nsis

Question

I'm writing an NSIS script, in this using some sections to execute EXE files. on depending output, I need to go back from the section to other custom pages but here nsis is moving to another section even though keeping of NSD_OnBack function or just calling the particular function
I have tried below 2 methods.
${NSD_OnBack} "callbackfunction"
call callbackfunction
//Section started
Section "validation" VALIDATION
DetailPrint "Executing Validation"
File "Folder_name\Validation.exe"
nsExec::Exec '"$INSTDIR\Validation.exe" $arg1 $arg2 $arg3'
IfFileExists "$INSTDIR\Output.txt" pass fail
pass:
FileOpen $chk "$INSTDIR\Output.txt" r
FileRead $chk $1
MessageBox MB_OK|MB_ICONSTOP "Validation_Output : in 1 $1"
Push $1
Push "true"
Call StrContains
Pop $3
${If} $3 == "true"
call someotherfunction
${ELSE}
goto fail
${ENDIF}
FileClose $chk
Delete $chk
fail:
MessageBox MB_OK|MB_ICONSTOP "fail"
//Here this call is not working
${NSD_OnBack} "callbackfunction"
SectionEnd
Function callbackfunction
GetDlgItem $0 $HWNDPARENT 2
${IF} $portalname == "centralised"
${IF} $username == ""
call CentralisedPage
${ENDIF}
${ELSE}
${IF} $username == ""
call SetCustom
${ENDIF}
${ENDIF}
Functionend
I am expecting to move other page based on EXE results.

Answer 1

${NSD_OnBack} is a callback for nsDialogs custom pages and it is invoked when the user presses the back button on that page, it is not relevant here.
Ideally you should collect all information before you get to the InstFiles page but if you can't do that then I would recommend that you just show a custom page after the InstFiles page if required.
If you absolutely need to execute sections multiple times you can use more than one InstFiles page:
!include LogicLib.nsh
!include WinMessages.nsh
!include nsDialogs.nsh
!include Sections.nsh
!include MUI2.nsh
!insertmacro MUI_PAGE_COMPONENTS
!define MUI_PAGE_CUSTOMFUNCTION_PRE Init1stStage
!insertmacro MUI_PAGE_INSTFILES
Page Custom MyCustomPageCreate
!define MUI_PAGE_CUSTOMFUNCTION_PRE Init2ndStage
!insertmacro MUI_PAGE_INSTFILES
!insertmacro MUI_PAGE_FINISH
!insertmacro MUI_LANGUAGE English
Var Needs2ndStage
Section "1st stage" SID_1
DetailPrint "1st stage"
MessageBox mb_yesno "Needs 2nd stage?" IDNO nope
StrCpy $Needs2ndStage 1
nope:
SectionEnd
Section "-2nd stage" SID_2
DetailPrint "2nd stage"
SectionEnd
Function Init1stStage
!insertmacro UnselectSection ${SID_2}
FunctionEnd
Function Init2ndStage
!insertmacro UnselectSection ${SID_1}
${IfThen} $Needs2ndStage = 0 ${|} Abort ${|}
FunctionEnd
Function MyCustomPageCreate
${IfThen} $Needs2ndStage = 0 ${|} Abort ${|}
!insertmacro SelectSection ${SID_2}
GetDlgItem $0 $hWndParent 1
SendMessage $0 ${WM_SETTEXT} "" "STR:C&ontinue"
GetDlgItem $0 $hWndParent 3
ShowWindow $0 0 ; Hide back
GetDlgItem $0 $hWndParent 2
EnableWindow $0 0 ; Disable cancel
!insertmacro MUI_HEADER_TEXT "Blah" "Blah blah blah"
nsDialogs::Create 1018
Pop $0
${NSD_CreateLabel} 0 0 100% 12u "Enter blah blah before you can enter the 2nd stage"
Pop $0
nsDialogs::Show
FunctionEnd