//沒有理由不堅持，慢慢走吧，後面的路或許很難，別放棄！
private void Form3_Load(object sender, EventArgs e)
        {
          //新增一個根節點
            TreeNode root = new TreeNode("遊戲型別");
            treeView1.Nodes.Add(root);
         //在資料庫查詢需要的型別，生成子節點
            string sql = "select * from Categories";
            DataTable table 
 
= DBHelper.Query(sql);
          //迴圈查找出資料庫的型別，生成子節點
            foreach (DataRow row in table.Rows)
            {
                string name = row["Name"].ToString();
               //int型別儲存id
                int id = (int)row["ID"];
                TreeNode node = new TreeNode(name);
                node.Tag 
 
= id;
               //初始值為0
                root.Tag = 0;
                root.Nodes.Add(node);
            }
         //讓treeview試圖在介面開啟時全部展開
            treeView1.ExpandAll();
        }

       //在點選對應的節點在datagridview的控制元件中顯示相應的試圖
        private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
        {
            
 
int id=(int)(treeView1.SelectedNode.Tag);
            int cateid=id;
            string sql = string.Format("select * from Products where CategoryID='{0}'", cateid);
            dataGridView1.DataSource = DBHelper.Query(sql);
        }
    }
}