How to free form inside of panel?

[dasa2]

Hi, I use 2 public procedures to view and delete forms in a panel.

To create form:

Code: Pascal  [Select][+][-]

1. procedure TfrmMain.CreateAndShowForm(Form: TForm; FormClass: TFormClass);
2. begin
3.   CloseActiveForm;
4.  
5.   Form:=FormClass.Create(Application);
6.   Form.BorderStyle:=bsNone;
7.   Form.Align := alClient;
8.   Form.Parent:= pnMain;
9.   Form.visible := True;
10.  
11.   Self.Caption:=Form.Caption;
12. end;

To remove form:

Code: Pascal  [Select][+][-]

1. procedure TfrmMain.CloseActiveForm;
2. begin
3.      while pnMain.controlcount > 0 do
4.            pnMain.controls[0].Free;
5. end;

From TfrmMain where the panel (pnMain) is in, I can create and delete forms by calling the procedures, but when I try to call the procedures from the form displayed in the panel, I get External: SIGSEGV when I try to delete the form and create another form using:

Code: Pascal  [Select][+][-]

1. frmMain.CreateAndShowForm(Nil, TfrmStart);

[Handoko]

Hello dasa2,
Welcome to the forum.

You put a form inside a panel of a form?
Wow, I never tried it. But it sounds not okay to me.
Maybe you should try using TFrame:

http://lazarus-ccr.sourceforge.net/docs/lcl/forms/tframe.html

Or using TPageControl or TNotebook.

[howardpc]

From TfrmMain where the panel (pnMain) is in, I can create and delete forms by calling the procedures, but when I try to call the procedures from the form displayed in the panel, I get External: SIGSEGV when I try to delete the form and create another form using:

Code: Pascal  [Select][+][-]

1. frmMain.CreateAndShowForm(Nil, TfrmStart);

Of course you get a SIGSEGV.

Code: Pascal  [Select][+][-]

1. CreateAndShowForm(Nil, TfrmStart);

translates into

Code: Pascal  [Select][+][-]

1. begin
2.   CloseActiveForm;
3.  
4.   Nil:=TfrmStart.Create(Application);
5.   ...

which is a complete nonsense.

Parenting a form to a TWinControl is a curious, non-standard behaviour.
As Handoko writes, far better to use TFrames or TCustomControls which are designed to need a parent.

[RAW]

I'm curious, what's the main reason of doing this ???

[dasa2]

From TfrmMain where the panel (pnMain) is in, I can create and delete forms by calling the procedures, but when I try to call the procedures from the form displayed in the panel, I get External: SIGSEGV when I try to delete the form and create another form using:

Code: Pascal  [Select][+][-]

1. frmMain.CreateAndShowForm(Nil, TfrmStart);

Of course you get a SIGSEGV.

Code: Pascal  [Select][+][-]

1. CreateAndShowForm(Nil, TfrmStart);

translates into

Code: Pascal  [Select][+][-]

1. begin
2.   CloseActiveForm;
3.  
4.   Nil:=TfrmStart.Create(Application);
5.   ...

which is a complete nonsense.

Parenting a form to a TWinControl is a curious, non-standard behaviour.
As Handoko writes, far better to use TFrames or TCustomControls which are designed to need a parent.

Sry, frmMain.CreateAndShowForm(frmStart, TfrmStart);


I try to create an application where I can view different forms without opening them in new windows. However, only one form may be available at a time.

I think it's like an MDI but without the ability to switch between the forms, maximize, minimize, and so on. Or as a website where every web page here is a form.

I need a nudge in the right direction.

[Blaazen]

You can dock any form to panel:

Code: Pascal  [Select][+][-]

1. Form2.Dock(Panel, Panel.ClientRect);

and undock

Code: Pascal  [Select][+][-]

1. Form2.Dock(nil, Rect);

where Rect is new size anmd position of the Form2.

[Handoko]

I try to create an application where I can view different forms without opening them in new windows. However, only one form may be available at a time.

If the layout is simple then you may use TNotebook. If it is complicated you can use TFrame. Here I wrote a demo showing how to use TNotebook to avoid using multi-forms:

http://forum.lazarus.freepascal.org/index.php/topic,39769.msg274036.html#msg274036

[alaa123456789]

https://youtu.be/1q8G8L4uABQ