Processing WM_CopyData message fails

[Krzychu]

Hi! I try to create a plugin in Lazarus which is based on existing open-source code. I use Windows and Messages classes.  WM_COPYDATA message should be used to communicate with the main programme and TCopyDataStruct should collect the data.
However, I found out that the messages between them are lost. After research I think it might be connected with Processing non-user messages in your window (http://wiki.freepascal.org/Win32/64_Interface#Processing_non-user_messages_in_your_window)

Now I try to implement the WndCallBack function, but I stuck with an error. I don't know what parameter should I pass to the procedure WMCopyData inside of the function WndCallback. I have already tried with:
- (var Msg: TCopyDataStruct) as in the procedure declaration. It raises an error: <<Sytax error, expected ")" but "IDENTIFIER MSG" found>>
- (Msg) - Error <<Error: Only class methods, class properties and class variables can be referred with class references>>
-() - Error <<Wrong number of parameters specified to call WmCopyData>>

Could you tell me how to make it work?

The code of my procedure:

Code: [Select]

procedure TForm1.WMCopyData(var Msg: TCopyDataStruct);


var
  sText: array[0..199] of Char;
  s, nr, kod, x, y, z : string;
  xx, yy : Double;
  err, n : Integer;


begin
    if Msg.dwData = 1 then
         Memo1.Clear;
         pkt := Msg.lpData;
         for n := 0 to 5000 do
          begin
           if pkt^[n].nr = '' then Break;
           Memo1.Lines.Add(pkt^[n].nr+' '+pkt^[n].k+' '+tostr(pkt^[n].x,2)+' '+tostr(pkt^[n].y,2)+' '+tostr(pkt^[n].z,3));
          end;
       end 

end; 

The WndCallBack function

Code: [Select]

function WndCallback(Ahwnd: HWND; uMsg: UINT; wParam: WParam; lParam: LParam):LRESULT; stdcall;

 begin
   case uMsg of WM_COPYDATA:
     begin
       Result := TForm1.WMCopyData();
       exit;
       end;
      else
      Result := CallWindowProc(PrevWndProc, Ahwnd, uMsg, WParam, LParam);
     end;

 end;                  

Declared with:

Code: [Select]

procedure WMCopyData(var Msg:TCopyDataStruct); message WM_COPYDATA;

[derek.john.evans]

This is the method i'm using. This unit is hacked from one of my projects. Would be nice to have something like this which is portable.

Code: Pascal  [Select][+][-]

1. unit Wim;
2.  
3. {$MODE objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   SysUtils, Windows;
9.  
10. type
11.   TWimCallBack = procedure(const AMessage: String);
12.  
13. procedure WimSetCallBack(const ASender: HWND; const ACallBack: TWimCallBack);
14. function WimSendMessage(const ASender: HWND; const AReceiver, AMessage: String): Boolean;
15.  
16. implementation
17.  
18. function WimSendMessage(const ASender: HWND; const AReceiver, AMessage: String): Boolean;
19. var
20.   LHandle: HWND;
21.   LCopyDataStruct: TCopyDataStruct;
22. begin
23.   LHandle := FindWindow(nil, pchar(AReceiver));
24.   Result := LHandle <> 0;
25.   if Result then begin
26.     LCopyDataStruct.dwData := 0;
27.     LCopyDataStruct.cbData := Length(AMessage) + 1;
28.     LCopyDataStruct.lpData := pchar(AMessage);
29.     SendMessage(LHandle, WM_COPYDATA, WPARAM(ASender), LPARAM(@LCopyDataStruct));
30.   end;
31. end;
32.  
33. var
34.  
35.   GWndProc: WNDPROC;
36.   GWimCallBack: TWimCallBack;
37.  
38. function WimProc(AHwnd: HWND; AMessage: UINT; AWParam: WParam; ALParam: LParam): LRESULT; stdcall;
39. var
40.   LCopyDataStruct: TCopyDataStruct;
41. begin
42.   if Assigned(GWimCallBack) and (AMessage = WM_COPYDATA) then begin
43.     LCopyDataStruct := PCopyDataStruct(ALParam)^;
44.     if LCopyDataStruct.dwData = 0 then begin
45.       GWimCallBack(pchar(LCopyDataStruct.lpData));
46.     end;
47.     Result := S_OK;
48.   end else begin
49.     Result := CallWindowProc(GWndProc, AHwnd, AMessage, AWParam, ALParam);
50.   end;
51. end;
52.  
53. procedure WimSetCallBack(const ASender: HWND; const ACallBack: TWimCallBack);
54. begin
55.   GWimCallBack := ACallBack;
56.   if GWndProc = nil then begin
57.     GWndProc := Windows.WNDPROC(SetWindowLongPtr(ASender, GWL_WNDPROC, PtrInt(@WimProc)));
58.   end;
59. end;
60.  
61. end.
62.  

To use, include unit wim, and:

Code: Pascal  [Select][+][-]

1. // This is your message receiver.
2. procedure GMyMessageCallBack(const AMessage: String);
3. begin
4.   ShowMessage(AMessage);
5. end;
6.  
7. procedure TForm1.FormCreate(Sender: TObject);
8. begin
9.   // Set the receiver callback.
10.   WimSetCallBack(Handle, @GMyMessageCallBack);
11.   // Set the caption. (I will explain why its here below)
12.   Caption := 'MyCaption';
13. end;
14.  
15. // Send a message like this.
16. procedure TForm1.Button1Click(Sender: TObject);
17. begin
18.   WimSendMessage(Handle, 'MyCaption', 'Hello There');
19. end;  
20.  

The way I use this is for single instances applications. I use WimSendMessage to send the ParamStr(1) (or, EmptyStr if there are no paramstr's) to a known window caption. If that succeeds, I halt the application, since another instance will pick up the filename and load it.

If it fails, then I must be the first instance, in which cause I handle the file loading. The reason why Caption must be set after the WinSendMessage, is so I dont pick up my own messages.

Anyway, if you have problems with the code, sing out. I guess I like this feature in a seperate unit, because, it makes porting the code easy. On other platforms, I just ignor WinSendMessage/WimSetCallBack

[Krzychu]

I have reproduced your code as you provided and I worked. Now I will try to use in the original project. I'll give you feedback soon
Thanks a lot for your help!

[Krzychu]

I managed to rewrite those codes and make it work in my project. So the problem was solved. Your hint was very useful. Thanks!