asp.net GridView控件中诗选全选和全不选功能

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Web.UI;
 using System.Web.UI.WebControls;
 using System.Data;
 using System.Data.SqlClient;
 using System.Configuration;
 
 public partial class _Default : System.Web.UI.Page
 {
     string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
     protected void Page_Load(object sender, EventArgs e)
     {
         SqlConnection conn = new SqlConnection(constr);
         conn.Open();
         string sql = "select * from student";
         SqlDataAdapter da = new SqlDataAdapter(sql, conn);
         DataSet ds = new DataSet();
         da.Fill(ds);
         GridView1.DataSource = ds;
         GridView1.DataBind();
     }
     protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
     {
         for (int i = ; i <= GridView1.Rows.Count - ; i++)
         {
             CheckBox chk = (CheckBox)GridView1.Rows[i].FindControl("chkCheck");
             if (chkAll.Checked == true)
             {
                 chk.Checked = true;
             }
             else
             {
                 chk.Checked = false;
             }
         }
     }
 }

<asp:TemplateField>

                    <ItemTemplate>
                        <asp:CheckBox ID="chkCheck" runat="server" />
                    </ItemTemplate>
</asp:TemplateField>

<configuration>
  <connectionStrings >
    <add name="constr" connectionString="server=.\sqlexpress;database=db2016;uid=sa;pwd=123;"/>
  </connectionStrings>
    <system.web>
      <compilation debug="true" targetFramework="4.0" />
    </system.web>
 
</configuration>