protected void districtDropDownList_SelectedIndexChanged(object sender, EventArgs e)
{
int id = Convert.ToInt32(districtDropDownList.SelectedValue);
thanaDropDownList.DataSource = dropDownManager.GetAllThana(id);
thanaDropDownList.DataTextField = "Name";
thanaDropDownList.DataValueField = "Id";
thanaDropDownList.DataBind();
ListItem liThana = new ListItem("Select Thana", "-1");
thanaDropDownList.Items.Insert(0, liThana);
}