launch application before uninstall

i need to launch a my .net application before uninstall main application. If my application end ok, uninstall process continue, otherwise stop it.

is it possible to do this? any suggestion or piece of code?

Your app should return 0 for success, and anything else for failure. Then your NSIS script could do this:

Function un.onInit
  ClearErrors
  ExecWait 'C:\ProgramFiles\YourCompany\YourNetApp.exe' $0
  ${If} ${Errors}    
    Abort        ;cancel uninstall 
  ${ElseIf} $0 <> 0
    Abort  ;cancel uninstall
${EndIf}
FunctionEnd 

thanks!!!

thank you very much.. it is perfect!