Creating Objects Dynamically on a frame - delphi

Question

I have two scenarios. One works, one does not. The first (the one that works) invloves a scrollbox sitting directly on a form that when a button is pushed it executes this code:
procedure TForm1.Button2Click(Sender: TObject);
begin
DrawPanel;
end;
procedure TForm1.DrawPanel;
begin
BuildPanel; //Resides on a seperate unit code pasted below
TestPanel.Height := 40;
TestPanel.Width := 100;
TestPanel.Left := Trunc(ScrollBox1.Width / 2) - Trunc(TestPanel.Width / 2);
TestPanel.Top := Trunc(ScrollBox1.Height / 2) - Trunc(TestPanel.Height / 2);
TestPanel.Visible := True;
TestPanel.Parent := ScrollBox1;
end;
unit Unit3;
interface
uses ExtCtrls;
Var
TestPanel : Tpanel;
Procedure BuildPanel;
implementation
procedure BuildPanel;
begin
TestPanel := TPanel.Create(Nil);
end;
end.
The code is identical except for a small difference in the second scenario. The scrollbox sits on a frame that is added to the Templates palette and then dropped down on the form. The button click calls:
procedure TForm1.Button1Click(Sender: TObject);
begin
TestFrame.DrawPanel;
end;
procedure TTestFrame.DrawPanel;
begin
BuildPanel; //Still points to the unit3 code above
TestPanel.Height := 40;
TestPanel.Width := 100;
TestPanel.Left := Trunc(ScrollBox1.Width / 2) - Trunc(TestPanel.Width / 2);
TestPanel.Top := Trunc(ScrollBox1.Height / 2) - Trunc(TestPanel.Height / 2);
TestPanel.Visible := True;
TestPanel.Parent := ScrollBox1;
end;
However the panel will not display in the scrollbox that sits on the frame, when triggered at runtime. I'm not really sure why, can anybody help out? I hope I was specific enough in my question, let me know if anything is unclear. Thanks in advance.
Here's all the code in order.....Hopefully it make it more clear:
//This is the form
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ExtCtrls, Unit2, Unit3;
type
TForm1 = class(TForm)
Button1: TButton;
TTestFrame1: TTestFrame;
ScrollBox1: TScrollBox;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure FormShow(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
TestFrame: TTestFrame;
Procedure DrawPanel;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
TestFrame.DrawPanel;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
DrawPanel;
end;
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
TestFrame.Free;
end;
procedure TForm1.FormShow(Sender: TObject);
begin
TestFrame := TTestFrame.Create(Form1);
end;
procedure TForm1.DrawPanel;
begin
BuildPanel;
TestPanel.Height := 40;
TestPanel.Width := 100;
TestPanel.Left := Trunc(ScrollBox1.Width / 2) - Trunc(TestPanel.Width / 2);
TestPanel.Top := Trunc(ScrollBox1.Height / 2) - Trunc(TestPanel.Height / 2);
TestPanel.Visible := True;
TestPanel.Parent := ScrollBox1;
end;
end.
//This is the frame
unit Unit2;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, Unit3;
type
TTestFrame = class(TFrame)
ScrollBox1: TScrollBox;
private
{ Private declarations }
public
{ Public declarations }
Procedure DrawPanel;
end;
implementation
{$R *.dfm}
{ TTestFrame }
procedure TTestFrame.DrawPanel;
begin
BuildPanel;
TestPanel.Height := 40;
TestPanel.Width := 100;
TestPanel.Left := Trunc(ScrollBox1.Width / 2) - Trunc(TestPanel.Width / 2);
TestPanel.Top := Trunc(ScrollBox1.Height / 2) - Trunc(TestPanel.Height / 2);
TestPanel.Visible := True;
TestPanel.Parent := ScrollBox1;
end;
end.
//This is the unit that mocks my data structure
//In reality it creates an Array of Tpanel that is part of a class.
unit Unit3;
interface
uses ExtCtrls;
Var
TestPanel : Tpanel;
Procedure BuildPanel;
implementation
procedure BuildPanel;
begin
TestPanel := TPanel.Create(Nil);
end;
end.

Answer 1

You just forgot to assign a parent to your dynamic created TestFrame.