Detect and uninstall old version of application in Inno Setup using its version number stored in registry

Question

I have an installer that write this line in the Windows registry

[Registry]
Root: "HKCU"; Subkey: "SOFTWARE\\W117GAMER"; ValueType: string         


        

Answer 1

With use of RegQueryStringValue function and CompareVersion function from Compare version strings in Inno Setup (your question), you can do:

#define MyAppVersion "2.6"

[Code]

function InitializeSetup(): Boolean;
var
  InstalledVersion: string;
  VersionDiff: Integer;
begin
  Result := True;
  if not RegQueryStringValue(
           HKCU, 'Software\My Program', 'DSVersionL4D2', InstalledVersion) then
  begin
    Log('No installed version detected');
  end
    else
  begin
    Log(Format('Found installed version %s', [InstalledVersion]));
    VersionDiff := CompareVersion(InstalledVersion, '{#MyAppVersion}');
    if VersionDiff < 0 then
    begin
      MsgBox(
        Format('You have an old version %s installed, will uninstall it.', [
          InstalledVersion]),
        mbInformation, MB_OK);
      { Uninstall old version here }
    end
      else
    if VersionDiff = 0 then
    begin
      MsgBox(
        'You have this version installed already, cancelling installation.',
        mbInformation, MB_OK);
      Result := False;
    end
      else
    begin
      MsgBox(
        Format(
          'You have newer version %s installed already, cancelling installation.', [
          InstalledVersion]),
        mbInformation, MB_OK);
      Result := False;
    end;
  end;
end;

Just plug-in an uninstallation code from some of the answers you have linked in your question.

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Though note that you do not need to write your own version registry value. There are DisplayVersion, VersionMajor and VersionMinor in the stnadard uninstall registry key.