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; https://stackoverflow.com/questions/11739317/how-to-detect-old-installation-and-offer-removal
[Code]
function GetUninstallString: string;
var
sUnInstPath: string;
sUnInstallString: String;
begin
Result := '';
sUnInstPath := ExpandConstant('Software\Microsoft\Windows\CurrentVersion\Uninstall\{{A227028A-40D7-4695-8BA9-41DF6A3895C7}_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\{A227028A-40D7-4695-8BA9-41DF6A3895C7}_is1', 'UninstallString') then { Your App GUID/ID }
begin
V := MsgBox(ExpandConstant('Hey! 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;
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