unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  PcsCopyDataStruct = ^TcsCopyDataStruct;
  TcsCopyDataStruct =
  packed record
    dwData : DWORD;
    cbData : DWORD;
    lpData : Pointer;
  end;
  TForm1 = class(TForm)
    Memo1: TMemo;
    Label1: TLabel;
    procedure FormShow(Sender: TObject);
    protected
      procedure WndProc(var msg : TMessage); override;

  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;
  dwMessage : DWORD;

implementation

uses Unit2;

{$R *.dfm}

procedure TForm1.WndProc(var msg : TMessage);
var
  cdWork : PcsCopyDataStruct;
begin
  if msg.Msg = dwMessage then
    begin
      cdWork := PcsCopyDataStruct(msg.LParam);
      if cdWork.dwData = dwMessage then
        begin
          Memo1.Lines.LoadFromFile(PChar(cdWork.lpData));
        end;
    end
  else
    begin
      inherited WndProc(msg);
    end;
end;

procedure TForm1.FormShow(Sender: TObject);
begin
  if (ParamCount > 0) and (FileExists(ParamStr(1))) then
    begin
      Label1.Caption := IntToStr(ParamCount);
      memo1.Lines.LoadFromFile(ParamStr(1));
    end;
end;

end.

program Project1;

uses
  Windows,
  Sysutils,
  Messages,
  Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

var
  dwMutex : DWORD;
  hWindow : DWORD;
  dwMessage : DWORD;
  cdWork : TcsCopyDataStruct;

begin
  dwMessage := RegisterWindowMessage('{44387CDE-D2EE-44A6-A97B-62627929A80F}');
  dwMutex := CreateMutex(nil, true, 'Project1');
  try
    if GetLastError <> ERROR_ALREADY_EXISTS then
      begin
        Application.Initialize;
        Application.CreateForm(TForm1, Form1);
  Application.Run;
      end
    else
      begin
        hWindow := FindWindow(nil, 'Project1');
        if hWindow <> 0 then
          begin
            if (ParamCount > 0) and FileExists(ParamStr(1)) then
              begin
                cdWork.dwData := dwMessage;
                cdWork.cbData := Length(ParamStr(1))+1;
                cdWork.lpData := AllocMem(cdWork.cbData);
                try
                  CopyMemory(cdWork.lpData, @ParamStr(1)[1], cdWork.cbData-1);
                  SendMessage(hWindow, WM_COPYDATA, 0, LPAram(@cdWork));
                finally
                  FreeMem(cdWork.lpData, cdWork.cbData);
                end;
              end;
          end;
      end;
    finally
      if dwMutex <> 0 then
        begin
          CloseHandle(dwMutex);
        end;
    end;
end.