hi all I want to write an text editor and to assign the txt files to it. My problem is that I want to have only one instance running and when a new file is opened to send the filename to the first app that is already running... (I want to do this using mutex). Here is a small test

DPR looks like this

uses
  Windows, Messages, SysUtils,
  Forms,
  wndMain in 'wndMain.pas' {frmMain};

{$R *.res}

var
  PrevWindow : HWND;
  S : string;
  CData : TCopyDataStruct;
begin 
  PrevWindow := 0;
  if OpenMutex(MUTEX_ALL_ACCESS, False, 'MyMutex') <> 0 then
  begin
  repeat
     PrevWindow:=FindWindow('TfrmMain', nil);
  until PrevWindow<>Application.Handle;

     if IsWindow(PrevWindow) then
     begin
        SendMessage(PrevWindow, WM_SYSCOMMAND, SC_RESTORE, 0);
        BringWindowToTop(PrevWindow);
        SetForegroundWindow(PrevWindow);

        if FileExists(ParamStr(1)) then
        begin
           S:=ParamStr(1);
           CData.dwData:=0;
           CData.lpData:=PChar(S);
           CData.cbData:=1+Length(S);

           SendMessage(PrevWindow, WM_COPYDATA, 0, DWORD(@CData) );
           end;
        end;
     end
   else
      CreateMutex(nil, False, 'MyMutex');

  Application.Initialize;
  Application.CreateForm(TfrmMain, frmMain);
  Application.Run;
end.

PAS:

type TfrmMain = class(TForm)
   memo: TMemo;
   private
      procedure WMCopyData ( var msg : TWMCopyData ) ; message WM_COPYDATA;
  public
     procedure OpenFile(f : String);
end;

var
  frmMain: TfrmMain;

implementation

{$R *.dfm}

procedure TfrmMain.WMCopyData ( var msg : TWMCopyData ) ;
var
   f : String;
begin
   f:=PChar(msg.CopyDataStruct.lpData);
   //ShowMessage(f);
   OpenFile(f);
end;

procedure TfrmMain.OpenFile(f : String);
begin
   memo.Clear;
   memo.Lines.LoadFromFile(f);
   Caption:=f;
end;

this code should be ok, but if i want to open a text file (from the second app), the first app receives a message like this:

thanks