private void btnLoad_Click(object sender, EventArgs e)
{
   DataTable dt = DataProvider.Instance.GetTable("select * from [tb_department]", "tb_department");
   treeList1.DataSource = dt;
}

private void btnShowValue_Click(object sender, EventArgs e)
{
   if (treeList1.FocusedNode == null) return;
   object row = treeList1.GetDataRecordByNode(treeList1.FocusedNode);
   DataRow dr = (row as DataRowView).Row;
   MessageBox.Show(dr["TagValue"].ToString());
}

/// <summary>
/// 数据提供者.
/// </summary>
public class DataProvider
{
   
   private static DataProvider _Instance = null;
   /// <summary>
   /// 数据提供者对象实例，因程序频繁请求数据,减少创建对象的次数。
   /// </summary>
   public static DataProvider Instance
   {
      get
      {
         if (_Instance == null)
         {
            _Instance = new DataProvider();
         }
         
         return _Instance;
      }
   }
   
   /// <summary>
   /// 提供数据表
   /// </summary>
   /// <param name="sql">SQL 查询语句</param>
   /// <param name="tableName">数据表名</param>
   /// <returns></returns>
   public DataTable GetTable(string sql, string tableName)
   {
      OleDbConnection conn = this.CreateConnection();
      OleDbCommand cmd = new OleDbCommand(sql, conn);
      OleDbDataAdapter adp = new OleDbDataAdapter(cmd);
      
      DataTable dt = new DataTable(tableName);
      adp.Fill(dt);
      
      conn.Close();
      conn.Dispose();
      return dt;
   }
   
   /// <summary>
   /// 创建一个OleDbConnection连接.
   /// </summary>
   /// <returns></returns>
   private System.Data.OleDb.OleDbConnection CreateConnection()
   {
      string connStr = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=data.mdb";
      OleDbConnection conn = new OleDbConnection(connStr);
      if (conn.State != ConnectionState.Connecting) conn.Open();
      return conn;
   }
}