Store in Seperate Datastructure

// CONTACT LIST CLASS UNIT

unit ContactList;

interface

uses
  Windows, Messages, SysUtils, Classes, VirtualTrees, Generics.Collections;

Type
   TUser = Class
   Public
     DisplayName,
     SkypeID            : String;
     UserNode           : PVirtualNode;
     Constructor Create(DispName, SkID : String);
   End;

Type
   TCategory = Class
   Private
     VT                 : TVirtualStringTree;
   Public
     Name               : String;
     ID                 : Integer;
     Users              : TObjectList<TUser>;
     CategoryNode       : PVirtualNode;
     Constructor Create(Tree : TVirtualStringTree; FName : String; FID : Integer);
     Destructor Destroy;
     Function AddUser(DispName, SkID : String):TUser;
   End;


Type
   TContactList = Class
   Private
    VT         : TVirtualStringTree;
   Public
    Categories : TObjectList<TCategory>;
    Constructor Create(Tree : TVirtualStringTree);
    Destructor Destroy;
    Function AddCategoryToList(DisplayName : String; ID : Integer):TCategory;
   End;

implementation



{ TCategory }

constructor TCategory.Create(Tree : TVirtualStringTree; FName: String; FID: Integer);
begin
 Users  := TObjectList<TUser>.Create;
 Name   := FName;
 ID     := FID;
 VT     := Tree;
end;

destructor TCategory.Destroy;
begin
 Users.Free;
end;


function TCategory.AddUser(DispName, SkID: String): TUser;
Var
 XUser : TUser;
begin

 XUser := TUser.Create(DispName, SkID);
 XUser.UserNode  := Self.VT.AddChild(CategoryNode,XUser);
 Self.Users.Add(XUser);
 Result := XUser;
end;



{ TUser }

constructor TUser.Create(DispName, SkID: String);
begin
   DisplayName := DispName;
   SkypeID := SkID;

end;

{ TContactList }

constructor TContactList.Create(Tree : TVirtualStringTree);
begin
  VT            := Tree;
  Categories    := TObjectList<TCategory>.Create;
end;

destructor TContactList.Destroy;
begin
  Categories.Free;
end;


Function TContactList.AddCategoryToList(DisplayName : String; ID : Integer):TCategory;
Var
 Ctg : TCategory;
Begin
 Ctg := TCategory.Create(VT, DisplayName,ID);
 Ctg.CategoryNode       := VT.AddChild(Nil, Ctg);
 Categories.Add(Ctg);
 Result := Ctg;
End;

end.

/////////////////////////////////////////////////////////////////////////////

// Main Unit!

unit uMain;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, VirtualTrees, Generics.Collections, ContactList, StdCtrls;


type
  TfrmMain = class(TForm)
    VT: TVirtualStringTree;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure VTGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
  private
    { Private declarations }
  public
    { Public declarations }
    ContactList : TContactList;
  end;

var
  frmMain: TfrmMain;

implementation

{$R *.dfm}


procedure TfrmMain.FormCreate(Sender: TObject);
Var
 I, J : Integer;
 Ctg : TCategory;
 User : TUser;
begin
 VT.NodeDataSize := SizeOf(Pointer);
 ContactList := TContactList.Create(VT);

 VT.BeginUpdate;
 for I := 1 to 1000 do
   begin
     Ctg := ContactList.AddCategoryToList('Category #'+IntToStr(I),Random(100));
     for J := 1 to 1000 do
     begin
       User := Ctg.AddUser('User #'+IntToStr(J),IntToStr(Random(3000)));
     end;

   end;
 VT.EndUpdate;

end;



procedure TfrmMain.FormDestroy(Sender: TObject);
begin
 ContactList.Free;
end;

procedure TfrmMain.VTGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
  Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
Var
 Obj : TObject;
 Ctg : TCategory;
 User : TUser;
begin

 Obj := TObject(Sender.GetNodeData(Node)^);

 if Obj is TCategory then
 begin
   Ctg := TCategory(Obj);
   case Column of
    0: CellText := Ctg.Name;
    1: CellText := IntToStr(Ctg.ID);
   end;
 end;

 if Obj is TUser then
 begin
   User := TUser(Obj);
   case Column of
    0: CellText := User.DisplayName;
    1: CellText := User.SkypeID;
   end;
 end;

end;

end.