Delphi - callback wrong code - delphi

Question

I believe I'm too tired, and I don't understand why a small callback doesn't work. I have 2 frames, created dynamically, I show the first one and at a click, I show the second one. When I finish the work with the second one, I want to show the first frame and free the second frame. Code is bellow:
code for the first frame:
procedure CommingBackFromFrame(aFrame:TFrame);
procedure TfraMain.ComingBackFromFrame(aFrame:TFrame);
begin
if Assigned(aFrame) then
begin
try
aFrame.Hide;
FreeAndNil(aFrame);
except on e:Exception do
//make a log
end;
Self.Show;//first frame show
end;
//code which creates the second frame
wFrm := TFrameType.Create(Application);//create the second frame
with wFrm do
begin
GoBack:=ComingBackFromFrame(wFrm);//error here
parent:=Self;
Show;
end; //with
Application.ProcessMessages;
code for the second frame:
TCallBack = procedure(aFrame:TFrame) of object;//callback declaration
TFrameType = class(Tframe)
...
private
FGoBack:TCallBack;
public
property GoBack:TCallBack read FGoBack write FGoBack;//publish callback
....
//at a moment, return to frame 1
if Assigned(fgoback) then
GoBack(Self);
Can anyone help me this simple thing?

Answer 1

BTW this is bad practice - free an object from its own code. Try to do that by message handler via PostMessage() to ensure that VCL finished all its work before freeing object.
Something like this:
TFrameType = class(TFrame)
protected
procedure FreeMe(var Msg TMessage) message WM_FREE_MY_FRAME;
public
procedure PostponedFree;
end;
procedure TFrameType.FreeMe(var Msg TMessage);
begin
Free;
end;
procedure TFrameType.PostponedFree;
begin
PostMessage(Self.Handle, WM_FREE_MY_FRAME, 0, 0);
end;
And call PostponedFree.
PS Code may not be accurate - I haven't started Delphi now. Sorry.

Answer 2

You're calling CommingBackFromFrame. So unless it's return-type is TCallBack it's obvious that it doesn't compile.
You might want to do GoBack:=CommingBackFromFrame; instead which subscribes the method CommingBackFromFrame to the even GoBack. Or perhaps GoBack:=wFrm.CommingBackFromFrame; depending on where CommingBackFromFrame is declared.
SideNote: You have a typo, the word is "coming" and not comming

Answer 3

Specify where CommingBackFromFrame comes from and what it does; without that, CodeInChaos` answer is the best you can get.
Is it part of wFrmDblDet, or part of your encompassing scope (the usage of with obfuscates that)?
In your current code, ComingBackFromFrame(wFrm) should return a TCallBack, but I think that was not your intent.
--jeroen

Answer 4

+1 to all.Thank you for your answers, especially to Abelisto et Jeroen, I've resolved now all the problems. Until Abelisto suggested PostMessage I've encountered lots of errors. Entire solution is bellow :
first frame, or FrmMain :
const WM_MY_MESSAGE = WM_USER + 0;
type
TfraMain = class(TFrame)
...
private
FFraChild : TFraChild;//second frame
procedure OnMyMessage(var Msg: TMessage); message WM_MY_MESSAGE;
procedure ComingBackFromFrame(aFrame:TFrame);
....
//step when the second frame is created
FFraChild := TFraChild.Create(Application);
with FFraChild do
begin
GoBack:= ComingBackFromFrame;
parent:=Self;
Show;
end; //with
....
procedure TfraMain.ComingBackFromFrame(aFrame:TFrame);
begin
if aFrame<>nil then
begin
try
aFrame.Hide;
PostMessage(Self.Handle,WM_MY_MESSAGE,0,0);
except on e:Exception do
// log error
end;
end;
end;
procedure TfraMain.OnMyMessage(var Msg: TMessage);
begin
FreeAndNil(FFraChild);
end;
second frame or frame 'child'
type
TCallBack = procedure(aFrame:TFrame) of object;
TFraChild = class(TFrame)
...
private
FGoBack:TCallBack;
public
property GoBack:TCallBack read FGoBack write FGoBack;
....
//after all operations with it are finished
if Assigned(fgoback) then
FGoBack(Self);
#Jeroen, I didn't found something related to Frames as the 'Release' existing in the TForm's implementation.
Best regards,
Radu