Delphi datasnap callback - BroadCast question

I'm again in a situation where I've spend an obscene amount of time on trying to customize datasnap callback samples to my needs. I'm old school OOP programmer and have several very large Object hierakies in my "toolbox" PODO style :-) .. and having this great datasnap feature, I want to utilize the forces of the callback.

BUT - when I implement it ... it simply fails ... (FASTMM4 reports mem leaks).

Try and create a simple VCL datasnap server - TCP. And add a butto开发者_StackOverflow中文版n and this source ...

procedure TForm1.Button1Click(Sender: TObject);
var
//  AObject : TObject;
  aJSONVal : TJSONValue;
begin
//  AObject := TObject.Create;
//  ServerContainer1.DSServer1.BroadcastObject('SomeChannel','SomeCallbackID', AObject);
//  AObject.Free;

  aJSONVal := TJSONObject.Create;
  ServerContainer1.DSServer1.BroadcastMessage('SomeChannel','SomeCallbackID',aJSONVal);
  // aJSONVal.Free; // Mat pointed out that this is done by the broadcast.
end;

It will work - as long as you keep using TJSONValue ... But try and switch the commented code - and you will see what I mean.

I could of course change all my existing code to JSON ... but that is simply not acceptable.

Does anyone have any idea on how to use the BroadcastOBJECT or NotifyOBJECT ?

Regards Bjarne

The object which you give to a Notify or Broadcast call is then owned by that call. Therefore do not call "AObject.Free;" or "aJSONVal.Free;". Doing so will often result in an Access Violation or other memory management related problems.

Note also that Broadcasted messages get put in a queue on the server and are later sent, in a different thread. Meaning, when your call to Broadcast returns, it hasn't actually sent the message to all the clients yet.

I hope that helps,

Mat

Possible answer: Your question was vague but based on what you've said, I'd start here:

Delphi XE help: (ms-help://embarcadero.rs_xe/vcl/DSServer.TDSServer.BroadcastObject.html):

function BroadcastObject(const ChannelName: String; const CallbackId: String; const Msg: TObject): boolean; overload;

The second overload sends an object to all client callbacks with a given registered callback identifier. For this purpose, an additional CallbackId parameter is required in the call."

You are using the second overload which takes 3 params - are your callback identifiers set up properly?