ASP.NET 2.0中给DropDownList服务器控件添加项的新方法

在ASP.NET 2.0中，可以在数据绑定时，通过设置DropDownList的AppendDataBoundItems属性为true,在数据绑定之前添加一个新的项目，并且这个新加的项目会保存在ViewState之中。下面就是一个实现的例子：

C#代码

<% ... @ Page Language = " C# "   %>
<% ... @ Import Namespace = " System.Data "   %>
<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

< script  runat ="server" > ...
  ICollection CreateDataSource()
   ... {
    DataTable dt  =   new  DataTable();
    DataRow dr;
    dt.Columns.Add( new  DataColumn( " id " ,  typeof (Int32)));
    dt.Columns.Add( new  DataColumn( " text " ,  typeof (string)));
     for  ( int  i  =   0 ; i  <   6 ; i ++ )
     ... {
      dr  =  dt.NewRow();
      dr[ 0 ]  =  i;
      dr[ 1 ]  =   " 列表项目  "   +  i.ToString();
      dt.Rows.Add(dr);
    }
    DataView dv  =   new  DataView(dt);
     return  dv;
  }
  protected  void  Button1_Click(object sender, EventArgs e)
   ... {
    Response.Write( " <li>DropDownList1 您选择的项目： "   +  DropDownList1.SelectedValue 
       +   "  ;  "   +  DropDownList1.SelectedItem.Text);
    Response.Write( " <li>DropDownList2 您选择的项目： "   +  DropDownList2.SelectedValue
       +   "  ;  "   +  DropDownList2.SelectedItem.Text);
  }

  protected  void  Page_Load(object sender, EventArgs e)
   ... {
     if  ( ! IsPostBack)
     ... {
      DropDownList1.AppendDataBoundItems  =   true ;
      DropDownList1.Items.Add( new  ListItem( " -- 请选择一个选择项 -- " ,  "" ));
      DropDownList2.DataSource  =  DropDownList1.DataSource  =  CreateDataSource();
      DropDownList2.DataTextField  =  DropDownList1.DataTextField  =   " text " ;
      DropDownList2.DataValueField  =  DropDownList1.DataValueField  =   " id " ;
      DropDownList1.DataBind();
      DropDownList2.DataBind();
    }
  }
</ script >

< html  xmlns ="http://www.w3.org/1999/xhtml" >
< head  runat ="server" >
   < title > DropDownList 补充例子 </ title >
</ head >
< body >
< form  id ="form1"  runat ="server" >
   < asp:DropDownList  ID ="DropDownList1"  runat ="server" >
   </ asp:DropDownList >
   < asp:DropDownList  ID ="DropDownList2"  runat ="server"  AppendDataBoundItems ="true" >
   < asp:ListItem  Text ="请选择"  Value ="" ></ asp:ListItem >
   </ asp:DropDownList >
   < asp:Button  ID ="Button1"  runat ="server"  Text ="得到选择的值"  OnClick ="Button1_Click"   />
</ form >
</ body >
</ html >

VB.NET代码

<% ... @ Page Language = " VB "  AutoEventWireup = " true "   %>

<% ... @ Import Namespace = " System.Data "   %>
<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

< script  runat ="server" > ...
  Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
    Response.Write( " <li>DropDownList1 您选择的项目： "   +  DropDownList1.SelectedValue  +  _
       "  ;  "   +  DropDownList1.SelectedItem.Text)
    Response.Write( " <li>DropDownList2 您选择的项目： "   +  DropDownList2.SelectedValue  +  _
       "  ;  "   +  DropDownList2.SelectedItem.Text)
  End Sub
  
  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
    If Not IsPostBack Then
      DropDownList1.AppendDataBoundItems  =  True
      DropDownList1.Items.Add(New ListItem( " -- 请选择一个选择项 -- " ,  "" ))
      DropDownList2.DataSource  =  CreateDataSource()
      DropDownList1.DataSource  =  CreateDataSource()
      DropDownList2.DataTextField  =   " text "
      DropDownList1.DataTextField  =   " text "
      DropDownList2.DataValueField  =   " id "
      DropDownList1.DataValueField  =   " id "
      DropDownList1.DataBind()
      DropDownList2.DataBind()
    End If
  End Sub
  
  Function CreateDataSource() As ICollection
    Dim dt As DataTable  =  New DataTable()
    Dim dr As DataRow
    dt.Columns.Add(New DataColumn( " id " , GetType(System.Int32)))
    dt.Columns.Add(New DataColumn( " text " , GetType(String)))
    For i As Integer  =   0  To  6
      dr  =  dt.NewRow()
      dr( 0 )  =  i
      dr( 1 )  =   " 列表项目  "   +  i.ToString()
      dt.Rows.Add(dr)
    Next
    Dim dv As DataView  =  New DataView(dt)
    Return dv
  End Function

</ script >

< html  xmlns ="http://www.w3.org/1999/xhtml" >
< head  id ="Head1"  runat ="server" >
   < title > DropDownList 补充例子 </ title >
</ head >
< body >
   < form  id ="form1"  runat ="server" >
     < asp:DropDownList  ID ="DropDownList1"  runat ="server" >
     </ asp:DropDownList >
     < asp:DropDownList  ID ="DropDownList2"  runat ="server"  AppendDataBoundItems ="true" >
       < asp:ListItem  Text ="请选择"  Value ="" ></ asp:ListItem >
     </ asp:DropDownList >
     < asp:Button  ID ="Button1"  runat ="server"  Text ="得到选择的值"  OnClick ="Button1_Click"   />
   </ form >
</ body >
</ html >

 

protected   void  DropDownList1_DataBound( object  sender, EventArgs e)
{
DropDownList1.Items.Insert( 0 , new  ListItem( " --请选择-- " ,  "" ));
}