ASP.NET中CheckBox的事件响应
我用AJAX的ToggleButtonExtender绑定了一个CheckBox，并且希望CheckBox发生CheckedChanged事件
时改变Label的内容。我用Button代替CheckBox试过，没有问题。但是换成CheckBox以后就不响应CheckedChanged事
件了，请问是为什么？代码如下：

public partial class _Default : System.Web.UI.Page
{
  Label label1 = new Label();
  ToggleButtonExtender tbe = new ToggleButtonExtender();
  CheckBox cb = new CheckBox();
  UpdatePanel up1 = new UpdatePanel();
  Panel panel1 = new Panel();

  protected void Page_Load(object sender, EventArgs e)
  {
  label1.Width = 90;
  label1.Text = "Label";

  cb.ID = "cb";
  cb.CheckedChanged += new EventHandler(cb_CheckedChanged);

  tbe.TargetControlID = "cb";
  tbe.CheckedImageUrl = "checked.png";
  tbe.UncheckedImageUrl = "unchecked.png";
  tbe.ImageHeight = 16;
  tbe.ImageWidth = 16;

  up1.ContentTemplateContainer.Controls.Add(label1);
  up1.ContentTemplateContainer.Controls.Add(cb);
  up1.ContentTemplateContainer.Controls.Add(tbe);

  panel1.Controls.Add(up1);

  panel1.Height = 100;
  panel1.Width = 100;
  panel1.BorderWidth = 1;
  panel1.Style.Add("position", "absolute");
  panel1.Style.Add("left", "200px");
  panel1.Style.Add("top", "200px");
  panel1.BorderColor = Color.Red;

  form1.Controls.Add(panel1);
  }

  void cb_CheckedChanged(object sender, EventArgs e)
  {
  label1.Text = DateTime.Now.ToLongTimeString().ToString();
  } 
}

------解决方案--------------------
CheckBox的autoPostpack没打开吧？？