At the beginning (InitializeSetup event function), check if the application is installed already (see GetUninstallString in the code below). If it is, ask user, what to do (see MsgBox use in the code and the first screenshot). If user chooses to update the existing installation, proceed normally. Inno Setup by default does not allow changing installation path of an existing installation (see DisableDirPage).
If uses chooses to install another copy, set AppId to a new unique value (GetAppId function in the code). This will make Inno Setup treat the installation as new, so it will prompt for the installation path. Update also UninstallDisplayName, so that the user can distinguish the installations when choosing which copy to uninstall (see GetAppIdentification and the third screenshot). Also update DefaultDirName to a new unique path (see GetAppIdentification and the third screenshot).
#define AppName "My Program"
#define AppVersion "1.5"
[Setup]
AppId={code:GetAppId}
AppName={#AppName}
AppVersion={#AppVersion}
UninstallDisplayName={#AppName} {#AppVersion}{code:GetAppIdentification}
UsePreviousLanguage=no # Needed when AppId is dynamic
DefaultDirName={autopf}\My Program{code:GetAppIdentification}
[Code]
var
Instance: string;
function GetAppId(Param: string): string;
begin
Result := '{#AppName}' + Instance;
end;
function GetAppIdentification(Param: string): string;
begin
if Instance <> '' then Result := ' (' + Instance + ')';
end;
function GetUninstallString(): string;
var
UninstallKey: string;
begin
UninstallKey :=
'Software\Microsoft\Windows\CurrentVersion\Uninstall\' + GetAppId('') + '_is1';
RegQueryStringValue(HKA, UninstallKey, 'UninstallString', Result);
Log(Result)
end;
function InitializeSetup(): Boolean;
var
Message: string;
Answer: Integer;
begin
Result := True;
if GetUninstallString() = '' then
begin
Log('Application is not installed yed, installing the first copy');
end
else
begin
Log('Application is installed already, asking what to do');
Message :=
'This program is installed already, ' +
'do you want to update the existing installation? ' +
'Press No to install another copy of the program';
Answer := MsgBox(Message, mbConfirmation, MB_YESNOCANCEL);
if Answer = IDYES then
begin
Log('User chose to update the installation');
end
else
if Answer = IDNO then
begin
Log('User chose to install another copy');
Instance := '2';
end
else
begin
Log('User chose to abort the installation');
Result := False;
end;
end;
end;
Now the question is what to do if there are already two installations. To make a third (or more), it's easy, just loop, increasing the value in Instance, until GetUninstallString returns an empty string. But had you wanted the user to be able to choose what copy to update, it would be more difficult. That's too much for one question.
What you want to do is quite complicated. If you want to keep the flexibility, I think that the easiest solution is to treat every new version as a separate software. In addition, when starting the installation, as a courtesy to those who want to keep the latest version only, offer to uninstall the previous (latest) installation automatically. If the user already has multiple installations, do nothing specific (or just inform the user).
