Inno setup: check for new updates - inno-setup

Question

After reading this post How to read a text file from the Internet resource?, I've adapted the code to what I need but I have some problems.
What I want to do is that when I run the setup, it checks for new updates. 1) If there isn't a new update, don't show any message. 2) And if there is a new update, show a message asking whether you want to download it or not.
This is my code:
procedure InitializeWizard;
var
DxLastVersion: string;
DxSetupVersion: String;
begin
if DownloadFile('http://dex.wotanksmods.com/latestver.txt', DxLastVersion) then
MsgBox(DxLastVersion, mbInformation, MB_YESNO)
else
MsgBox(DxLastVersion, mbError, MB_OK)
end;
Thanks so much in advanced.

Answer 1

Since you've decided to use a common version string pattern, you'll need a function which will parse and compare a version string of your setup and the one downloaded from your site. And because there is no such function built-in in Inno Setup, you'll need to have your own one.
I've seen a few functions for comparing version strings, like e.g. the one used in this script, but I've decided to write my own. It can detect an invalid version string, and treats the missing version chunks as to be 0, which causes comparison of version strings like follows to be equal:
1.2.3
1.2.3.0.0.0
The following script might do what you want (the setup version is defined by the AppVersion directive):
[Setup]
AppName=My Program
AppVersion=1.2.3
DefaultDirName={pf}\My Program
[Code]
const
SetupURL = 'http://dex.wotanksmods.com/setup.exe';
VersionURL = 'http://dex.wotanksmods.com/latestver.txt';
type
TIntegerArray = array of Integer;
TCompareResult = (
crLesser,
crEquals,
crGreater
);
function Max(A, B: Integer): Integer;
begin
if A > B then Result := A else Result := B;
end;
function CompareValue(A, B: Integer): TCompareResult;
begin
if A = B then
Result := crEquals
else
if A < B then
Result := crLesser
else
Result := crGreater;
end;
function AddVersionChunk(const S: string; var A: TIntegerArray): Integer;
var
Chunk: Integer;
begin
Chunk := StrToIntDef(S, -1);
if Chunk <> -1 then
begin
Result := GetArrayLength(A) + 1;
SetArrayLength(A, Result);
A[Result - 1] := Chunk;
end
else
RaiseException('Invalid format of version string');
end;
function ParseVersionStr(const S: string; var A: TIntegerArray): Integer;
var
I: Integer;
Count: Integer;
Index: Integer;
begin
Count := 0;
Index := 1;
for I := 1 to Length(S) do
begin
case S[I] of
'.':
begin
AddVersionChunk(Copy(S, Index, Count), A);
Count := 0;
Index := I + 1;
end;
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
begin
Count := Count + 1;
end;
else
RaiseException('Invalid char in version string');
end;
end;
Result := AddVersionChunk(Copy(S, Index, Count), A);
end;
function GetVersionValue(const A: TIntegerArray; Index,
Length: Integer): Integer;
begin
Result := 0;
if (Index >= 0) and (Index < Length) then
Result := A[Index];
end;
function CompareVersionStr(const A, B: string): TCompareResult;
var
I: Integer;
VerLenA, VerLenB: Integer;
VerIntA, VerIntB: TIntegerArray;
begin
Result := crEquals;
VerLenA := ParseVersionStr(A, VerIntA);
VerLenB := ParseVersionStr(B, VerIntB);
for I := 0 to Max(VerLenA, VerLenB) - 1 do
begin
Result := CompareValue(GetVersionValue(VerIntA, I, VerLenA),
GetVersionValue(VerIntB, I, VerLenB));
if Result <> crEquals then
Exit;
end;
end;
function DownloadFile(const URL: string; var Response: string): Boolean;
var
WinHttpRequest: Variant;
begin
Result := True;
try
WinHttpRequest := CreateOleObject('WinHttp.WinHttpRequest.5.1');
WinHttpRequest.Open('GET', URL, False);
WinHttpRequest.Send;
Response := WinHttpRequest.ResponseText;
except
Result := False;
Response := GetExceptionMessage;
end;
end;
function InitializeSetup: Boolean;
var
ErrorCode: Integer;
SetupVersion: string;
LatestVersion: string;
begin
Result := True;
if DownloadFile(VersionURL, LatestVersion) then
begin
SetupVersion := '{#SetupSetting('AppVersion')}';
if CompareVersionStr(LatestVersion, SetupVersion) = crGreater then
begin
if MsgBox('There is a newer version of this setup available. Do ' +
'you want to visit the site ?', mbConfirmation, MB_YESNO) = IDYES then
begin
Result := not ShellExec('', SetupURL, '', '', SW_SHOW, ewNoWait,
ErrorCode);
end;
end;
end;
end;