procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit3.SetFocus;  //获取焦点
  Edit3.SelStart:=StrToInt(Edit1.text); //设置字符的起始位置
  Edit3.SelLength:=StrToInt(Edit2.text);//设置字符的个数
end;

procedure TForm1.Edit1Change(Sender: TObject);
var
  str:string;
begin
  str:='';
  str:=Edit1.Text;
  if Length(str)>0 then
  if not(str[Length(str)]in ['0'..'9',#8]) then
  begin
    Application.MessageBox('请输入数字(','提示',MB_OKCANCEL+MB_ICONINFORMATION);
　　 Edit1.Text:=LeftStr(Str,Length(Str)-1);
  end;
  Edit1.SelStart:=Length(Edit1.text);
end;

procedure TForm1.Edit1Enter(Sender: TObject);
begin
  if Sender is TEdit then
    (Sender as TEdit).Color := $00C8FFFF
  else if Sender is TComboBox then
    (Sender as TComboBox).Color := $00C8FFFF;
end;

procedure TForm1.Edit1Exit(Sender: TObject);
begin
  if Sender is TEdit then
    (Sender as TEdit).Color := clWhite
  else if Sender is TComboBox then
    (Sender as TComboBox).Color := clWhite;
end;

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if not (Key in ['a'..'z','A'..'Z',#8]) then
  begin
    Application.MessageBox('只能输入英文字符！', '提示', MB_OKCANCEL + MB_ICONINFORMATION);
    Key := #0;
  end;
end;

procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  Edit2.Text := IntToStr(Key);
  if Shift = [ssShift] then
    Edit1.Text := 'Shift'
  else if Shift = [ssAlt] then
    Edit1.Text := 'Alt'
  else if Shift = [ssCtrl] then
    Edit1.Text := 'Ctrl'
  else
    Edit1.Text := '';
end;