Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

{ 
You can perform communication between your application using Windows messages 
exchange mechanism. We can use HWND_BROADCAST value for first parameter for 
SendMessage function for suppressing finding of forms' in other applications HANDLE. 
For using HWND_BROADCAST we should register our messages in Windows. 
In example below we will inform about our form's top position) 

Das Beispiel zeigt, wie zwischen zwei Applikationen eine Meldung (Message) 
verschickt werden kann. Die Meldung mit wird mit SendMessage verschickt. 
Der erst Parameter ist HWND_BROADCAST, beim zweite ist unsere Message. 
Das untenstehende Beispiel informiert z.B uber die Top-Position unserer Form}


 // 1. Define type of your message structure, it could be something like this: 
// 1. Definiere eine eigene Message Struktur: 


type
   TWMMYMessage = record
     Msg: Cardinal;   // ( first is the message ID ) 
    Handle: HWND;    // ( this is the wParam, Handle of sender) 
    Info: Longint;   // ( this is lParam, pointer to our data) 
    Result: Longint;
   end;

   // 2. Override your form''s DefaultHandler method and add 
  //    method for handling your message, like this 
  // 2. Die DefaultHandler Methode zu uberschreiben 

  TForm1 = class(TForm)
     ...public
     { Public declarations }
     ...procedure DefaultHandler(var Message); override;
     procedure WMMYMessage(var Msg: TWMMYMessage);
     ...end;


   // 3. Declare message variable: 
  // 3. Die Message-Variablen deklarieren: 

var
   WM_OURMESSAGE: DWORD;

   // 4. Insert realisation of DefaultHandler and our message handler methods: 
  // 4. DefaultHandler Implementation: 

procedure TForm1.DefaultHandler(var Message);
 var
   ee: TWMMYMessage;
 begin
   with TMessage(Message) do
   begin
     if (Msg = WM_OURMESSAGE) then
      begin
       ee.Msg    := Msg;
       ee.Handle := wParam;
       ee.Info   := lParam;
       // Checking if this message is not from us 
      if ee.Handle <> Handle then
         WMMYMessage(ee);
     end
     else
       inherited DefaultHandler(Message);
   end;
 end;

 procedure TForm1.WMMYMessage(var Msg: TWMMYMessage);
 begin
   label1.Caption := Format('Our another form handle :%d', [Msg.Handle]);
   Label2.Caption := Format('Our another form top :%d', [Msg.Info]);
 end;

 // 5. Add registration of your message that you could 
//    handle the HWND_BROADCAST messages: 
// 5. Die Message registrieren. 

initialization
   WM_OURMESSAGE := RegisterWindowMessage('Our broadcast message');

   // 6. Add the message sending somewhere: 

procedure TForm1.Button1Click(Sender: TObject);
 begin
   SendMessage(HWND_BROADCAST, WM_OURMESSAGE, Handle, Top);
 end;