unit TSTPanel;

interface

uses
 Controls, Classes, ExtCtrls, StdCtrls;

type

 TTSTPanel = class;
 TTSTDropDownList = class;

 TTSTDropDownList = class(TPersistent)
 private
   FOwner : TTSTPanel;
   FActive: Boolean;
   FItemList: TStrings;
   procedure SetActive(const Value: Boolean);
   procedure SetItemList(const Value: TStrings);
   procedure UpdateItems;
 protected
   function GetOwner: TPersistent; override;
 public
   constructor Create(AOwner : TTSTPanel);
   destructor Destroy; override;
 published
   property Active : Boolean read FActive write SetActive;
   property ItemList : TStrings read FItemList write SetItemList;
 end;

 TTSTPanel = class(TCustomPanel)
 private
   FDropDownList: TTSTDropDownList;
   FComboBox : TComboBox;
   procedure SetDropDownList(const Value: TTSTDropDownList);
 public
   constructor Create(AOwner: TComponent); override;
 published
   property DropDownList : TTSTDropDownList read FDropDownList write SetDropDownList;
 end;

implementation

uses SysUtils;

{ TTSTPanel }

constructor TTSTPanel.Create(AOwner: TComponent);
begin
 inherited;
 FDropDownList := TTSTDropDownList.Create(Self);
end;

procedure TTSTPanel.SetDropDownList(const Value: TTSTDropDownList);
begin
 FDropDownList := Value;
end;

{ TTSTDropDownList }

constructor TTSTDropDownList.Create(AOwner: TTSTPanel);
begin
 FOwner := AOwner;
 FItemList := TStringList.Create;
end;

destructor TTSTDropDownList.Destroy;
begin
 FItemList.Free;
 inherited;
end;

function TTSTDropDownList.GetOwner: TPersistent;
begin
 Result := FOwner;
end;

procedure TTSTDropDownList.SetActive(const Value: Boolean);
begin
 FActive := Value;
 if FActive then
 begin
   FOwner.FComboBox := TComboBox.Create(FOwner);
   FOwner.FComboBox.Parent := FOwner;
   UpdateItems;
 end
 else
 begin
   if Assigned(FOwner.FComboBox) then
     FreeAndNil(FOwner.FComboBox);
 end;
end;

procedure TTSTDropDownList.SetItemList(const Value: TStrings);
begin
 FItemList.Assign(Value);
 if FActive then
   UpdateItems;
end;

procedure TTSTDropDownList.UpdateItems;
begin
 FOwner.FComboBox.Items.Assign(FItemList);
end;

end.

procedure TTSTPanel.Loaded;
begin
 inherited Loaded;
 if DropDownList.Active then DropDownList.UpdateItems;
end;
end;

begin
 ADropDown := TTSTDropDownList.Create;
 TSTPanel.DropDownList := ADropDown;
end;

procedure TTSTPanel.SetDropDownList(const Value: TTSTDropDownList);
begin
FDropDownList.Assign(Value);
end;

constructor TTSTDropDownList.Create(AOwner: TTSTPanel);
begin
FOwner := AOwner;
FItemList := TStringList.Create;
FItemList.OnChange := DoChange;
end;

procedure TTSTDropDownList.DoChange(Sender: TObject);
begin
 UpdateItems;
end;

procedure TTSTDropDownList.UpdateItems;
begin
 if Assigned(FOwner.FComboBox) and Active then
   FOwner.FComboBox.Items.Assign(FItemList);
end;

if FActive then UpdateItems;