Inno Setup (이노셋업) 이전 버전 확인 후 Uninstall / Install

function GetUninstallString: string;
var
  sUnInstPath: string;
  sUnInstallString: String;
begin
  Result := '';
  sUnInstPath := ExpandConstant('Software\Microsoft\Windows\CurrentVersion\Uninstall\{{B77EBEF8-649A-4420-8EC9-14E43D09072D}_is1'); //Your App GUID/ID
  sUnInstallString := '';
  if not RegQueryStringValue(HKLM, sUnInstPath, 'UninstallString', sUnInstallString) then
    RegQueryStringValue(HKCU, sUnInstPath, 'UninstallString', sUnInstallString);
  Result := sUnInstallString;
end;

function IsUpgrade: Boolean;
begin
  Result := (GetUninstallString() <> '');
end;

function InitializeSetup: Boolean;
var
  V: Integer;
  iResultCode: Integer;
  sUnInstallString: string;
begin
  Result := True; // in case when no previous version is found
  if RegValueExists(HKEY_LOCAL_MACHINE,'Software\Microsoft\Windows\CurrentVersion\Uninstall\{B77EBEF8-649A-4420-8EC9-14E43D09072D}_is1', 'UninstallString') then  //Your App GUID/ID
  begin
    V := MsgBox(ExpandConstant('An old version of app was detected. Do you want to uninstall it?'), mbInformation, MB_YESNO); //Custom Message if App installed
    if V = IDYES then
    begin
      sUnInstallString := GetUninstallString();
      sUnInstallString :=  RemoveQuotes(sUnInstallString);
      Exec(ExpandConstant(sUnInstallString), '', '', SW_SHOW, ewWaitUntilTerminated, iResultCode);
      Result := True; //if you want to proceed after uninstall
      //Exit; //if you want to quit after uninstall
    end
    else
      Result := False; //when older version present and not uninstalled
  end;
end;