unit Unit1;    interface    uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;    type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
  TMyNode = class(TPersistent)
  private
  i:string;
  public
    ParentNodes, SubNodes: array[0..2] of TMyNode;        constructor Create;
    destructor Destroy; override;
  end;    var
  Form1: TForm1;
  mynode: TMyNode;    implementation    {$R *.dfm}    procedure TForm1.Button1Click(Sender: TObject);
begin
  mynode := TMyNode.Create;
  mynodes[0] := TMynode.Create;
  mynode.SubNodes[0] := TMyNode.Create;
end;    procedure TForm1.Button2Click(Sender: TObject);
begin
  freeandnil(mynode);
end;    { TMyNode }    constructor TMyNode.Create;
begin
   i:='create';
end;
 调用栈是什么，会不会发生重复释放的问题，如何表达更清楚？
怎么能看到对象释放的过程，以及那些对象没有被释放掉？
destructor TMyNode.Destroy;
var
  i: integer;
begin
  for i := 0 to 2 do
  begin
    if assigned(ParentNodes[i]) then
      FreeAndNil(ParentNodes[i]);
    if assigned(SubNodes[i]) then
      FreeAndNil(SubNodes[i]);
  end;
  inherited;
end;    end.