Lazarus表单按代码调整大小

下面的代码是一个简单的示例:

unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs;

type

  { TForm1 }

  TForm1 = class(TForm)
    procedure FormDblClick(Sender: TObject);
    procedure FormResize(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;
  h : Integer;
implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.FormDblClick(Sender: TObject);
begin
  ShowMessage(h.ToString);
end;

procedure TForm1.FormResize(Sender: TObject);
begin
   h := Form1.Height;
   Form1.Height:=200; //please note this line
end;

end.   

如果我注释掉标记的行,双击它可以看到表单高度的变化。

我做错了什么?