C#省市县三级联动（listbox)

//省
private void lbProvince_SelectedIndexChanged(object sender, EventArgs e)
{
DataTable table = new DataTable();
string strconn = "Data Source=.\\SQLEXPRESS;Initial Catalog=My_Test;Integrated Security=True";
SqlConnection sqlconn = new SqlConnection(strconn);
string strsql = "select * from AreaFull where AreaPid='"+(lbProvince.SelectedIndex+1)+"'";
SqlDataAdapter adp = new SqlDataAdapter(strsql, strconn);
adp.Fill(table);
lbCity.DataSource = table;
lbCity.DisplayMember = "AreaName";  //要显示在控件中的字段
lbCity.ValueMember = "AreaId";    //显示项的实际值
}

//市
private void lbCity_SelectedIndexChanged(object sender, EventArgs e)
{
DataTable table = new DataTable();
string strconn = "Data Source=.\\SQLEXPRESS;Initial Catalog=My_Test;Integrated Security=True";
SqlConnection sqlconn = new SqlConnection(strconn);
string strsql = "select * from AreaFull where AreaPid in(select AreaId from AreaFull where AreaName='"+lbCity.Text.ToString()+"')";
//string strsql = "select * from AreaFull where AreaId = '"+lbCity.Text+"'";
SqlDataAdapter adp = new SqlDataAdapter(strsql, strconn);
adp.Fill(table);
lbCounty.DataSource = table;
lbCounty.DisplayMember = "AreaName"; //要显示在控件中的字段
}
//加载窗体
private void Form1_Load(object sender, EventArgs e)
{
DataTable table = new DataTable();
string strconn = "Data Source=.\\SQLEXPRESS;Initial Catalog=My_Test;Integrated Security=True";
SqlConnection sqlconn = new SqlConnection(strconn);
string strsql = "select * from AreaFull where AreaPid=0";
SqlDataAdapter adp = new SqlDataAdapter(strsql, strconn);
adp.Fill(table);
lbProvince.DataSource = table;
lbProvince.DisplayMember = "AreaName";  //要显示在控件中的字段
//lbProvince.ValueMember = "AreaId";  //显示项的实际值
}