Check All Checkbox In GridView To Bulk Edit Or Update ASP.NET C# NET

 chkselect all put autopostback=true;

protected void chkSelectAll_CheckedChanged
                               (object sender, EventArgs e)
{
 CheckBox chkAll = 
    (CheckBox)GridView1.HeaderRow.FindControl("chkSelectAll");
 if (chkAll.Checked == true)
 {
   foreach (GridViewRow gvRow in GridView1.Rows)
   {
    CheckBox chkSel = 
         (CheckBox)gvRow.FindControl("chkSelect");
    chkSel.Checked = true;
    TextBox txtname = (TextBox)gvRow.FindControl("txtName");
    TextBox txtlocation = (TextBox)gvRow.FindControl("txtLocation");
    txtname.ReadOnly = false;
    txtlocation.ReadOnly = false;
    txtname.ForeColor = System.Drawing.Color.Black;
    txtlocation.ForeColor = System.Drawing.Color.Black;
   }
 }
 else
 {
  foreach (GridViewRow gvRow in GridView1.Rows)
  {
   CheckBox chkSel = (CheckBox)gvRow.FindControl("chkSelect");
   chkSel.Checked = false;
   TextBox txtname = (TextBox)gvRow.FindControl("txtName");
   TextBox txtlocation = (TextBox)gvRow.FindControl("txtLocation");
   txtname.ReadOnly = true;
   txtlocation.ReadOnly = true;
   txtname.ForeColor = System.Drawing.Color.Blue;
   txtlocation.ForeColor = System.Drawing.Color.Blue;
   }
  }
}