communicate between 2 progs with sendmessage.

[JeanCremers 1]

Ok, so one prog does for instance 

HWND hwnd = FindWindow(NULL, "myprog");
if (hwnd)
  SendMessage(hwnd, WM_USER, 0, 0);

 

And what exactly should the other prog do? I have this, but it's not working.

in form constructor Application->HookMainWindow(&AppHook);

 

bool __fastcall TMainForm::AppHook(TMessage &Message)
{
if (Message.Msg == WM_USER)
  {

  Application->MessageBox("", "", MB_OK);
  return true;
  }
return false;
}

 

But i'm not getting any msg there.

 

Thanks.

Edited October 28, 2023 by JeanCremers
spelling

[Remy Lebeau 1396]

On 10/27/2023 at 3:08 PM, JeanCremers said:

HWND hwnd = FindWindow(NULL, "myprog");

 

Is "myprog" the title for your program's TApplication window or TForm window?  It makes a big difference.  I'm suspecting the latter.

Quote

I have this, but it's not working.

...

i'm not getting any msg there.

You are installing a message handler for the TApplication window.  To handle messages for the TForm window, override the TForm's virtual WndProc() method instead:

void __fastcall TMainForm::WndProc(TMessage &Message)
{
  if (Message.Msg == WM_USER)
  {
    Application->MessageBox("", "", MB_OK);
    Message.Result = 1;
  }
  else
    TForm::WndProc(Message);
}

That being said, WM_USER is not a good choice for inter-process communications.  Use WM_APP or RegisterWindowMessage() instead.

Edited October 28, 2023 by Remy Lebeau

[JeanCremers 1]

Thanks Remy.

I'm getting EOSError 'System Error. Code 1411, Class does not exist.'

This is c++builder 6 🙂

 

Edit, i also tried 

void __fastcall TAstroClockMainForm::ApplicationEvents1Message(tagMSG &Msg,
      bool &Handled)
{
if (Msg.message == WM_APP)
  Application->MessageBox("", "", MB_OK);

}

and

 

HWND hwnd = FindWindow("TAstroclockMainForm", NULL);
if (hwnd)
  SendMessage(hwnd, WM_APP, 0, 0);

Edited October 28, 2023 by JeanCremers

[Remy Lebeau 1396]

18 hours ago, JeanCremers said:

Thanks Remy.

I'm getting EOSError 'System Error. Code 1411, Class does not exist.'

Sorry, my bad. I left out the part where the overriden WndProc() needs to pass unhandled messages to the default handler. I have corrected my example.

Quote

This is c++builder 6 🙂

What I showed applies to all C++Builder versions.

Quote

i also tried 

void __fastcall TAstroClockMainForm::ApplicationEvents1Message(tagMSG &Msg,
      bool &Handled)
{
if (Msg.message == WM_APP)
  Application->MessageBox("", "", MB_OK);

}

That won't work. That event is triggered only for messages that are posted to the main thread message queue. Which your example message is not.

Quote

and

HWND hwnd = FindWindow("TAstroclockMainForm", NULL);
if (hwnd)
  SendMessage(hwnd, WM_APP, 0, 0);

That likely won't work, either, because your MainForm's class name is TMainForm not TAstroclockMainForm (unless what you have shown is not your real code).

Edited October 28, 2023 by Remy Lebeau

[JeanCremers 1]

Thanks a bunch again Remy, i've got it working like a charm. 

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