[Solved] A component that contains another

[lainz]

Hi, I'm working on a component that's like this:

- Panel
-- Listbox

A panel containing a listbox. The problem I have is if I add in 'published' the ListBox property and I change it with the object inspector then when I run the program the properties (say for example Items property) is not loaded at all.

I create the ListBox on create event of the panel container.

The source code is here:
https://github.com/bgrabitmap/bgracontrols/blob/master/bclistbox.pas

In the source I not publish the property because it doesn't works and well but is usable at least without it.

[minesadorada]

Just a guess (a long time since I did it)
Use SetSubComponent for the listbox in the register proc and a Propertyeditor for it?

Example here: http://wiki.freepascal.org/Poweredby#Other_uses

[lainz]

Thanks for your reply, is too late here I will try tomorrow.

[balazsszekely]

Hi @lainz,

Only publish the properties you need, something like this:

Code: Pascal  [Select][+][-]

1. //...
2. type
3.  TBCPaperListBox = class(TBCPaperPanel)
4.   private
5.     FListBox: TBCListBox;
6.     function GetListBoxItems: TStrings;
7.     procedure SetListBoxItems(AItems: TStrings);
8.   public
9.     constructor Create(TheOwner: TComponent); override;
10.   published
11.     property Items: TStrings read GetListBoxItems write SetListBoxItems;
12.   end;        
13.  
14. //...
15. { TBCPaperListBox }
16.  
17. constructor TBCPaperListBox.Create(TheOwner: TComponent);
18. begin
19.   inherited Create(TheOwner);
20.   Self.ChildSizing.ControlsPerLine := 1;
21.   Self.ChildSizing.LeftRightSPacing := 4;
22.   Self.ChildSizing.TopBottomSpacing := 5;
23.   FListBox := TBCListBox.Create(Self);
24.   FListBox.Align := alClient;
25.   FListBox.Parent := Self;
26. end;
27.  
28. function TBCPaperListBox.GetListBoxItems: TStrings;
29. begin
30.   Result := FListBox.Items;
31. end;
32.  
33. procedure TBCPaperListBox.SetListBoxItems(AItems: TStrings);
34. begin
35.   if FListBox.Items <> AItems then
36.     FListBox.Items := AItems;
37. end;

[lainz]

Oh I see. That has some kind of advantages, for example that the user for error clears the ListBox assigned in the property I publish, with your way it will not happen.

Edit: Well tested the minesadorada code and works fine. To avoid the user to clear the property we must register the property editor for the class, as displayed in the wiki.