Mega Code Archive
Communicating between your applications
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Title: Communicating between your applications.
Question: I want to perform communication between two my applications or between two instances of my application.
Answer:
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.
For performing this you could make the following:
(In example below we will inform about our form's top position)
1. Define type of your message structure, it could be something like this:
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
TForm1 = class(TForm)
...
public
{ Public declarations }
...
procedure DefaultHandler(var Message); override;
procedure WMMYMessage(var Msg: TWMMYMessage);
...
end;
3. Declare message variable:
var
WM_OURMESSAGE: DWORD;
4. Insert realisation of DefaultHandler and our message handler methods:
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:
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;
7. Compile and run two copies of your application and test it functionality.
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