asp.net 2.0中gridview里嵌套dropdownlist

在asp.net 2.0中,在一个gridview里,可以嵌套进一个dropdownlist,这是十分容易的事情,而这里讲的是,
在每个dropdownlist里,都绑定的是不同的内容,比如在northwind数据库中,可以用GRIDVIEW显示出
每个category类别,同时每一行的category类别里可以已dropdonwlist下拉框的形式,列出该分类下的所有
产品.下面介绍实现的方法

首先是页面部分的代码
 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnRowDataBound="GridView1_RowDataBound">
<Columns>

<asp:BoundField DataField="CategoryID" HeaderText="CategoryID" />

<asp:BoundField DataField="CategoryName" HeaderText="Category Name" />

<asp:TemplateField HeaderText="Products">

<ItemTemplate>

<asp:DropDownList ID="DropDownList1" runat="server">

</asp:DropDownList>

</ItemTemplate>

</asp:TemplateField>

</Columns>

</asp:GridView>

在codebehind部分,
 protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {

            // This is because Table[1] contains Categories

            GridView1.DataSource = GetDataSet().Tables[1];

            GridView1.DataBind();

        }

    }
    private DataSet GetDataSet()
    {

        string query = @"SELECT p.CategoryID,p.ProductID, p.ProductName FROM Products p

SELECT c.CategoryID,c.CategoryName FROM Categories c";

        string connectionString = "Server=localhost;Database=Northwind;user id=sa;password=123456";

        SqlConnection myConnection = new SqlConnection(connectionString);

        SqlDataAdapter ad = new SqlDataAdapter(query, myConnection);

        DataSet ds = new DataSet();

        ad.Fill(ds);

        return ds;

    }
    在上面的代码中,首先我们通过典型的dataset返回,绑定到gridview上去,注意这里sql语句里有两句,第一句是返回产品,第二句是返回所有的类别category,而在绑定gridview时,我们用
  GridView1.DataSource = GetDataSet().Tables[1];,将第一个table表里的category记录绑定到gridview里去,接下来,我们要处理模版列中的dropdownlist了，这个可以在row_databound事件中写入代码,如下
   protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        DataTable myTable = new DataTable();

        DataColumn productIDColumn = new DataColumn("ProductID");

        DataColumn productNameColumn = new DataColumn("ProductName");

        myTable.Columns.Add(productIDColumn);

        myTable.Columns.Add(productNameColumn);

        DataSet ds = new DataSet();

        ds = GetDataSet();

        int categoryID = 0;

        string expression = String.Empty;

        if (e.Row.RowType == DataControlRowType.DataRow)
        {

            categoryID = Int32.Parse(e.Row.Cells[0].Text);

            expression = "CategoryID = " + categoryID;

            DropDownList ddl = (DropDownList)e.Row.FindControl("DropDownList1");

            DataRow[] rows = ds.Tables[0].Select(expression);

            foreach (DataRow row in rows)
            {

                DataRow newRow = myTable.NewRow();

                newRow["ProductID"] = row["ProductID"];

                newRow["ProductName"] = row["ProductName"];

                myTable.Rows.Add(newRow);

            }

            ddl.DataSource = myTable;

            ddl.DataTextField = "ProductName";

            ddl.DataValueField = "ProductID";

            ddl.DataBind();

        }

  }
  这里的原理大致如下:
首先，我们建立了一个datatable,包含了productid,productname列,然后将其与 gridview绑定,之后再用
 categoryID = Int32.Parse(e.Row.Cells[0].Text);

            expression = "CategoryID = " + categoryID;
构造一个筛选表达式,这里指定为categoryID,然后通过
 DropDownList ddl = (DropDownList)e.Row.FindControl("DropDownList1");
           DataRow[] rows = ds.Tables[0].Select(expression);
  ,找出符合其类别等于某一categoryID的所有产品,这里构造出datarow集合了,最后,使用循环
,将某类别下的产品全部添加到datatable中去,最后将datatable和dropdownlist绑定,就实现功能了