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Delphi Form ownership

Posted on 2016-09-03
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Last Modified: 2016-09-22
I want to create multiple instances of a (sub)Tform  that all are owned by another (main)Tform from where they where created. If the user closes a (sub)form, it should be destroyed and not be owned by the mainform. If the Mainform is closed, all subforms should all be destroyed. I guess i can do this with a new TComonentlist, but is there any functionality in the form that i can use? (probably also a TComonentlist) ?
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Question by:Sunsales
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4 Comments
 
LVL 28

Expert Comment

by:Sinisa Vuk
ID: 41783248
Delphi's Ownership handle such things....
So... create forms under Main Form ownership .... and on sub form destroy - Main form will be notified... and sub form will be excluded from component list...
//main form
procedure TfrmMain.StartSubForm();
var
  childform: TSubForm;
begin
   childform := TSubForm.Create(frmMain);
   childform.Show; //show and do not block main form
end;

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Child form's OnClose event:
procedure TSubForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Self.Hide;
  Action:=caFree;  //sub form want to be free.....
end;

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1
 

Author Comment

by:Sunsales
ID: 41783301
Can I use a TobjectList instead of the Tform as owner and still get an automatic delete in the TobjectList  when i free the form?
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LVL 38

Accepted Solution

by:
Geert Gruwez earned 2000 total points
ID: 41783587
there is no point in maintaining your own list
all components create with an owner are stored inside the parent container component
delphi does by default what you ask

except ... when you create components/forms with nil as owner
SubForm := TSubForm.Create(nil);

an object instance which is freed doens't have an owner
it just doesn't exist anymore

mind the difference between closing/hiding and free a form
1
 

Author Closing Comment

by:Sunsales
ID: 41811427
Thanx
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