Check/Prevent Windows Shutdown (NSIS) - nsis

Question

To summarize, I need to check and/or prevent a user if he/she decides to shutdown the computer while the installer is running. Now I've researched for a while and came up with the following:
${If} ${AtMostWinXP}
System::Call `kernel32::GetModuleHandle(i0)i.r3`
System::Call `user32::CreateWindowEx(i0,t"STATIC",t"MyApp",i0,i0,i0,i0,i0,i$HWNDPARENT,i0,ir3,i0)i.r1`
${ElseIf} ${AtLeastVista}
System::Call `user32::ShutdownBlockReasonCreate(ir1,w"MyApp is running and still needs to clean up before shutting down!")i.r0`
${EndIf}
However the above snippet isn't working. Am I missing something? I've tried using just:
System::Call `kernel32::GetModuleHandle(i0)i.r3`
System::Call `user32::CreateWindowEx(i0,t"STATIC",t"MyApp",i0,i0,i0,i0,i0,i$HWNDPARENT,i0,ir3,i0)i.r1`
System::Call `user32::ShutdownBlockReasonCreate(ir1,w"MyApp is running and still needs to clean up before shutting down!")i.r0`
As the first two calls are meant for Windows XP and earlier and the third call is meant for Windows Vista or later but is ignored by Windows XP and earlier I believe (I have no evidence to support this theory). This too isn't working.
Also, I can use user32::ShutdownBlockReasonCreate(ir1,w"$(PreventShutdown)")i.r0 instead of using the entire string in the above snippet for different language support, right?

Answer 1

Your code for Windows XP makes no sense, the window needs to handle WM_QUERYENDSESSION to block the shutdown. Luckily NSIS already handles WM_QUERYENDSESSION for you.
Use something like this for Vista and later:
LoadLanguageFile "${NSISDIR}\Contrib\Language Files\English.nlf"
LangString BlockReason ${LANG_ENGLISH} "Installer blah blah"
LoadLanguageFile "${NSISDIR}\Contrib\Language Files\Swedish.nlf"
LangString BlockReason ${LANG_SWEDISH} "Installer bork bork"
!include nsDialogs.nsh ; For WS_CHILD
!define /ifndef WS_POPUP 0x80000000
!include LogicLib.nsh
Function CreateShutdownBlockReason
StrCpy $1 $hwndParent
${If} $1 Z= 0 ; $hwndParent is 0, create a new window for silent installers
System::Call 'USER32::CreateWindowEx(i0, t "STATIC", t "$(^Name)", i ${WS_CHILD}|${WS_POPUP}, i0, i0, i0, i0, p r1, i0, i0, i0)p.r1'
${EndIf}
System::Call 'USER32::ShutdownBlockReasonCreate(p r1, w "$(BlockReason)")'
FunctionEnd
Function .onInit
IfSilent 0 +2
Call CreateShutdownBlockReason ; .onGuiInit is not executed in silent installers
FunctionEnd
Function .onGuiInit
Call CreateShutdownBlockReason
FunctionEnd
I'm not sure if a silent installer will be able to block the shutdown but this is the best you can do without a plug-in.