That is what I expect for that case.
Try this - Close the form after creating the components. ie press button 1, then close
the form.
You are correct, it you free them then you will get the notifications.
The problem only arises when the Form (the components owners) does the destroy/free
instead.
Myles.
-----Original Message-----
From: Carl Reynolds [SMTP:[EMAIL PROTECTED]]
Sent: Tuesday, July 06, 1999 4:20 PM
To: Multiple recipients of list delphi
Subject: RE: [DUG]: Notification Bug on Remove???
Hmmm. Well, I knocked together a sample form to test things:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;
type
TMyComponent = class(TComponent)
protected
procedure Notification(AComponent: TComponent; Operation: TOperation);
override;
end;
TMyComponent2 = class(TComponent)
protected
constructor CreateMe(POwner: TComponent; PNotifyComponent: TComponent);
end;
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Button3: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
private
MyComponent: TMyComponent;
MyComponent2: TMyComponent2;
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TMyComponent.Notification(AComponent: TComponent; Operation: TOperation);
begin
inherited;
if (AComponent is TMyComponent2) and (Operation = opRemove) then begin
ShowMessage('Can''t say I wasn''t told...');
end;
end;
constructor TMyComponent2.CreateMe(POwner: TComponent; PNotifyComponent: TComponent);
begin
inherited Create(POwner);
FreeNotification(PNotifyComponent);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
MyComponent := TMyComponent.Create(Self);
MyComponent2 := TMyComponent2.CreateMe(Self, MyComponent);
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
MyComponent2.Free;
end;
procedure TForm1.Button3Click(Sender: TObject);
begin
MyComponent.Free;
end;
end.
and if I click the buttons in order, my component receives OpRemove notification when
I click button 2, as expected. And they're non-visual components, so no problem
there. And both component have the same owner - I tried it with nil as an owner and
it still worked. That's using FreeNotification.
>Can't use FreeNotification as it checks who the owner of the two components are and
>if they are the same it does not add it to the >FreeNotifies list. Tried that one
>already.
Well, it seemed to. Did I miss something?
Cheers,
Carl Reynolds Ph: +64-9-4154790
CJN Technologies Ltd. Fax: +64-9-4154791
[EMAIL PROTECTED] DDI: +64-9-4154795
PO Box 302-278, North Harbour, Auckland, New Zealand
12 Piermark Drive, North Harbour Estate, Auckland, NZ
Visit our website at http://www.cjntech.co.nz/
-----Original Message-----
From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED]]
Sent: Tuesday, July 06, 1999 3:14 PM
To: '[EMAIL PROTECTED]'
Subject: RE: [DUG]: Notification Bug on Remove???
That's the whole POINT it DOES NOT WORK. Have now spent several hours tracing through
the source code using the Debugger to check what was occurring - I did not believe
this was the problem initially.
I only found it during testing of Creation Order of Components and having Contructors
throw exceptions during Form creation to test the components destructors cleanup code
(which failed of course) as no Notification( , OpRemove) was received as the
Non-Visual components were destroyed.
I was VERY surprised to find the OpRemove notifications not working for Non-Visual
components eg TDatabase, TQuery etc - Any TControl or TWinControl does not have this
problem, as they get destroyed in TWinControl.Destory, and hence do not have this
problem,
Can't use FreeNotification as it checks who the owner of the two components are and if
they are the same it does not add it to the FreeNotifies list. Tried that one already.
Seems like the only solution is to change TComponent.DestroyComponents to call
RemoveComponent instead of Remove.
Myles.
-----Original Message-----
From: Carl Reynolds [SMTP:[EMAIL PROTECTED]]
Sent: Tuesday, July 06, 1999 2:36 PM
To: Multiple recipients of list delphi
Subject: RE: [DUG]: Notification Bug on Remove???
If you want a component (TMyComponent) to be notified about another component being
freed, eg. when one of its sub-components (TMySubComponent) is removed, call
TMySubComponent.FreeNotification(TMyComponent) at some point, usually during
TMySubComponent's construction. Then TMyComponent gets an OpRemove notification just
before TMySubComponent is freed. That's without using InsertComponent or
RemoveComponent - is that what you meant?
If you want to let other components on a form know of a component's impending demise,
and those other components haven't been given FreeNotification from the component,
then the form has to do the work (iterating through its components list to let the
appropriate components know as required). Hope that helps...
Cheers,
Carl Reynolds Ph: +64-9-4154790
CJN Technologies Ltd. Fax: +64-9-4154791
[EMAIL PROTECTED] DDI: +64-9-4154795
PO Box 302-278, North Harbour, Auckland, New Zealand
12 Piermark Drive, North Harbour Estate, Auckland, NZ
Visit our website at http://www.cjntech.co.nz/
-----Original Message-----
From: Myles Penlington [SMTP:[EMAIL PROTECTED]]
Sent: Tuesday, July 06, 1999 11:53 AM
To: Multiple recipients of list delphi
Subject: [DUG]: Notification Bug on Remove???
What's your understanding of the Delphi Notification mechanism??
My understanding is that if a TComponent or its descendant is removed from a Form then
all other components on the Form will be sent a Notification ( MyComponent, OpRemove)
- of course its owner is the form - this all stuff in the DFM.
However this appears to be NOT the case. No OpRemove notification sent is if the
component being removed is descended from TComponent eg TQuery etc - It does work if
you remove a TControl or TWinControl.
e.g. If you put a TButton , TDatabase and a TQuery on a form (in that order), the
TDatabase does not get notified of the destruction of the TQuery - not that it matters
in this case (but we have other cases that do matter - our own components).
The offending code is in TComponent.
procedure TComponent.DestroyComponents; // This is called from TComponent.Destroy
var
Instance: TComponent;
begin
while FComponents <> nil do
begin
Instance := FComponents.Last;
Remove(Instance); // IF THIS WAS RemoveComponent then all would be okay, or if
TComponent.Remove did not set the owner to NIL.
Instance.Destroy;
end;
end;
Do I have my understanding wrong or is this a serious bug/stuff up??
Can someone (Richard/Nic?) explain why it has been done this way??
By the way all the components do get a Notification( , OpInsert), when they are
created from the DFM, they just do not get the OpRemove when the form is destroyed,
this occurs as TComponent.Create does a InsertComponent which does do a notification.
Comments Please.
Regards
Myles Penlington
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