动态创建控件 list index out of bounds解决方法

动态创建控件 list index out of bounds
运行时点击按钮出现list index out of bounds(3)，之后是list index out of bounds(2)，再按则正常，什么问题呢？

[code=Delphi(Pascal)][/code]

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls, Vcl.ComCtrls;

type
  TControlClass=class of TControl;
  TForm1 = class(TForm)
  MonthCalendar1: TMonthCalendar;
  Memo1: TMemo;
  ColorBox1: TColorBox;
  RadioGroup1: TRadioGroup;
  Button1: TButton;
  Label1: TLabel;
  procedure Button1Click(Sender: TObject);
  private
  { Private declarations }
  procedure createControlObj(ControlClass:TControlClass);
  public
  { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.createControlObj(ControlClass:TControlClass);
var AControlObj:TControl;
begin
  AControlObj:=ControlClass.Create(self);//根据不同的类类型，动态创建对象
  AControlObj.Parent:=self;//指定TForm1为控件的容器
  AControlObj.Name:=AControlObj.ClassName;//以类名作为控件名
  AControlObj.SetBounds(10,10,250,150);//设置控件边界
  Label1.Caption:=AControlObj.ClassName;
end;

procedure TForm1.Button1Click(Sender: TObject);
const
//定义一个以控件类类型为元素的数组
  ContrlClassArry:array[0..2] of
  TControlClass=(TMonthCalendar,TMemo,TColorBox);
var
  i:Integer;
begin
//清空已经动态生成的控件
for i := 0 to controlcount-1 do
  if (Controls[i] is TMonthCalendar) or (Controls[i] is TMemo)
  or (Controls[i] is TColorBox) then
  Controls[i].Free;
  //调用构造函数，动态生成用户选定的控件
  createControlObj(ContrlClassArry[RadioGroup1.ItemIndex]);
end;

end.


[解决办法]
for i := 0 to controlcount-1 do
==>
for i := controlcount-1 downto 0 do

[解决办法]
因为每删除一个对象，ControlCount就会发生变化。所以，要从大到小的删除。
[解决办法]
我来解释下吧：你释放一个控件后，controlcount的值同时也改变了，而此时i的值在增加,而controlcount的值在减少