Question

Using the JEDI VCL library with Delphi, I put a JvDockServer on the main form,
and on another that should be docked to the main form, I have JvDockClient using dock style JvDockVIDVCStyle.

While Docking works great, I would like to be notified when a client form changes from docked to undocked (floating) mode.

Answer 1

Update The JVCL is now modified to contain this feature built in! The TForm’s built in events is now fired when you dock a form. Check out the DockingInCode demo in the JEDI JVCL, which now (as of March 27 2012) contains samples of Docking and Undocking events firing. TForm.OnEndDock is now fired when docking, as is TForm.OnUnDock on undocking. Sorry about the names, those area already in TForm and I didn’t choose them!

OLD ANSWER for historical reasons:

You would like a notification when a form has been made to float. TForm already has OnUnDock and OnEndDock, but these are (sadly) not fired when you dock and undock using the Jedi VCL Dock Manager.

The best method I can think of to do this is to modify the JVCL.

Modify JvDockSupportControl.pas, method TJvDockCustomControl.WndProc:

procedure TJvDockCustomControl.WndProc(var Msg: TMessage);
var
  CMUnDockClient: TCMUnDockClient;
  DockableForm: TJvDockableForm;
  allow:Boolean;
begin
  if Msg.Msg = CM_UNDOCKCLIENT then
  begin
    CMUnDockClient := TCMUnDockClient(Msg);
    // new code starts here
    if CMUnDockClient.Client is TForm then begin
      allow := true;
      if Assigned(TForm(CMUnDockClient.Client).OnUnDock) then
        TForm(CMUnDockClient.Client).OnUnDock(Self,CMUnDockClient.Client,TWinControl(nil),allow);
//      if not allow then
//        exit; // currently JvDocking has already deleted you from the dock tree, so we can't honor this.
    end;
    // new code ends here
   if CMUnDockClient.Client is TJvDockableForm then
   begin
    ...

Unfortunately this is an oversight in the design of the components, and if you log it in the Jedi Bug Tracker, and post the link to it here. JvDocking internals are complex, sadly, but the above hack might get you going as of today.

Alternative to editing JVCL is to make your own Style, based on the Dock Style that you prefer to use, and add OnDock and OnFloat events to it. For example, if you are using the VID (Visual Interdev) dock style, copy JvDockVIDStyle.pas to your own unit, and rename it to something else.

Find this procedure in the code:

    procedure TJvDockVIDTree.WindowProc(var Msg: TMessage);

leave the existing code in that function and add the following at the bottom:

if (Msg.msg =CM_UNDOCKCLIENT)and Assigned(FOnUndock) then
    FOnUndock( TObject(Msg.Client))

I think that I should write a better version of the above and put it into the JVCL JvDocking, since it’s an intuitive thing. In addition OnEndDock should probably be made to function. OnStartDock is incompatible with JvDocking, so I can’t add that.