Call C# DLL from Inno Setup with callback

I have a running Inno Setup script, wherein I use innocallback.dll by Sherlock Software.

This DLL wraps a procedure of mine so that it can be passed to a C# DLL.

I don't want to use this DLL, I want to call my exported C# method directly and pass to it the callback procedure.

My question is:

How can I pass my Inno Setup procedure (@mycallback) to my C# DLL so that I can use it as my delegate/UnmanagedFunctionPointer?

As I said this code works, but I want to use as little external DLL's as possible.

Here is my code:

Inno Setup Script

type
  TTimerProc=procedure();
  TProgressCallback=procedure(progress:Integer);
    
function WrapProgressProc(callback:TProgressCallback; paramcount:integer):longword;
  external 'wrapcallback@files:innocallback.dll stdcall';

function Test(callback:longword): String;
  external 'Test@files:ExposeTestLibrary.dll stdcall';

var
  endProgram : Boolean;

procedure mycallback(progress:Integer);
begin
  MsgBox(IntToStr(progress), mbInformation, MB_OK); 
  if progress > 15 then
  begin
    endProgram := True;
  end
end;
  
function InitializeSetup:boolean;
var
  progCallBack   : longword;
  callback       : longword;
  msg            : longword;
  msg2           : widestring;
begin
  endProgram := False;
  progCallBack:= WrapProgressProc(@mycallback,1); //Our proc has 1 arguments
  Test(progCallBack);
  result:=true;
end;

And this is my C# code

public class TestClass
{
    [UnmanagedFunctionPointer(CallingConvention.StdCall)]
    public delegate void ReportProgress(uint progress);

    public static ReportProgress m_reportProgess;
    static uint m_iProgress;
    
    [DllExport("Test", CallingConvention = CallingConvention.StdCall)]
    static int Test(ReportProgress rProg)
    {
        m_iProgress = 0;
        m_reportProgess = rProg;
        System.Timers.Timer pTimer = new System.Timers.Timer();
        pTimer.Elapsed += aTimer_Elapsed;
        pTimer.Interval = 1000;
        pTimer.Enabled = true;
        GC.KeepAlive(pTimer);
        return 0;
    }

    static void aTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
    {
        m_iProgress++;
        m_reportProgess(m_iProgress);
    }
}

There's no way to drop the usage of the wrapping InnoCallback library since you simply cannot define a callback procedure with a calling convention of your choice in Inno Setup, nor you can define a callback with the register calling convention (the one specific to Delphi compiler) in your C# library.

Due to this limit you must use an external library, which wraps a callback method from Inno Setup into a function with a calling convention that your library can consume (InnoCallback uses stdcall for that).

So, what you're asking for would be possible if you were writing your library in a language that supports Delphi's register calling convention. Out of curiosity, in Delphi you could write e.g.:

library MyLib;

type
  TMyCallback = procedure(IntParam: Integer; StrParam: WideString) of object;

procedure CallMeBack(Callback: TMyCallback); stdcall;
begin
  Callback(123, 'Hello!');
end;

exports
  CallMeBack;

begin
end.

And in Inno Setup then (without any wrapping library):

[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program

[Files]
Source: "MyLib.dll"; Flags: dontcopy

[Code]
type
  TMyCallback = procedure(IntParam: Integer; StrParam: WideString);

procedure CallMeBack(Callback: TMyCallback);
  external 'CallMeBack@files:mylib.dll stdcall';

procedure MyCallback(IntParam: Integer; StrParam: WideString);
begin
  MsgBox(Format('IntParam: %d; StrParam: %s', [IntParam, StrParam]),
    mbInformation, MB_OK);
end;

procedure InitializeWizard;
begin
  CallMeBack(@MyCallback);
end;