Send string data from Thread to main form

Question

In Dephi, I create a thread, like this, which will send message to main form from time to time

Procedure TMyThread.SendLog(I: Integer);
Var
  Log: array[0..2         


        

Answer 1

If you have D2009 or later version, there is another way to post messages to your main form. TThread.Queue is an asynchronous call from a thread, where a method or procedure can be executed in the main thread.

The advantage here is that the frame to set up the message passing is less complex. Just pass your callback method when creating your thread. No handles and no explicit handling of string allocation/deallocation.

Type
  TMyCallback = procedure(const s : String) of object;

  TMyThread = class(TThread)
    private
      FCallback : TMyCallback;
      procedure Execute; override;
      procedure SendLog(I: Integer);
    public
      constructor Create(aCallback : TMyCallback);
  end;

constructor TMyThread.Create(aCallback: TMyCallback);
begin
  inherited Create(false);
  FCallback := aCallback;
end;

procedure TMyThread.SendLog(I: Integer);
begin
  if not Assigned(FCallback) then
    Exit;
  Self.Queue(  // Executed later in the main thread
    procedure
    begin
      FCallback( 'Log: current stag is ' + IntToStr(I));
    end
  );
end;

procedure TMyThread.Execute;
var
  I: Integer;
begin
  for I := 0 to 1024 * 65536 do
  begin
    if ((I mod 65536) = 0) then
    begin
      SendLog(I);
    End;
  End;
end;

---

procedure TMyForm.TheCallback(const msg : String);
begin
  // Show msg
end;

procedure TMyForm.StartBackgroundTask(Sender : TObject);
begin
  ... 
  FMyThread := TMyThread.Create(TheCallback);
  ...
end;