Edit1Enter事件无法触发的问题

这是我调试的程序，可以实现

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Edit1: TEdit;
procedure Edit1Enter(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Edit1Enter(Sender: TObject);
begin
button1.Enabled:=true;
end;

end.