checkbox在repeater中checked值无法改变

.cs:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DataTable dt = new DataTable();
dt.Columns.Add("name");
DataRow dr = dt.NewRow();
dr[0] = "123";
dt.Rows.Add(dr);
this.Repeater1.DataSource = dt;
this.Repeater1.DataBind();
}
CheckBox cbx = (CheckBox)this.Repeater1.Items[0].FindControl("CheckBox1");
TextBox txt1 = (TextBox)this.Repeater1.Items[0].FindControl("TextBox1");
txt1.Text = cbx.Checked.ToString();
}
.aspx: