dropdownlist 联动 ，第二个dropdownlist的取值总是（第一个选项）怎么解决？

Question

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml.Linq;
using webwinscom.DAL.proClassIdTableAdapters;namespace webwinscom.admin
{
    public partial class addpro : System.Web.UI.Page
    {   
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {           
               
            }
        }
        protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string x = DropDownList1.SelectedValue;
            string xx = "SELECT  [Pro_name], [pro_ClassId] FROM [Pro_NameID] where pro_ClassId=" + x;
          
            SqlDataSource2.SelectCommand = xx;                 
        }            
    }
}

Answer 1

dropdownlist 联动 ，第二个dropdownlist的取值总是（第一个选项）怎么解决？  

Answer 2

DropDownList1启用autopostback了么？

Answer 3

还是不懂。。指的是选定项?用SelectedValue="";设定选定项。。

Answer 4

     <tr >
                <td class="style3" > 
                    <asp:Label ID="Label1" runat="server" Text="所属父类："></asp:Label>
                    <asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="SqlDataSource1" 
                        DataTextField="protype" DataValueField="ProClass" AutoPostBack="True" 
                        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
                    </asp:DropDownList>
                    <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
                        ConnectionString="<%$ ConnectionStrings:T_winscomConnectionString %>" 
                        SelectCommand="SELECT DISTINCT [protype], [ProClass] FROM [Pro_TypeID]">
                    </asp:SqlDataSource>
                </td>
       </tr>
        <tr>
                <td class="style3" > 
                    <asp:Label ID="Label2" runat="server" Text="类别名称："></asp:Label>                    <asp:DropDownList ID="DropDownList2" runat="server" 
                        DataSourceID="SqlDataSource2" DataTextField="Pro_name" 
                        DataValueField="pro_ClassId" AutoPostBack="True" 
                        onselectedindexchanged="DropDownList2_SelectedIndexChanged">
                    </asp:DropDownList>
                    <asp:SqlDataSource ID="SqlDataSource2" runat="server" 
                        ConnectionString="<%$ ConnectionStrings:T_winscomConnectionString %>" 
                        SelectCommand="SELECT [Pro_name], [pro_ClassId] FROM [Pro_NameID]">
                    </asp:SqlDataSource>
                </td>
           </tr> 

Answer 5

dropdownlist似乎选不中没value的项

Answer 6

DropDownList2.Items.FindByText("").Selected = true;//根据text
DropDownList2.Items.FindByValue("").Selected = true;//根据value

Answer 7

删除SqlDataSource ID="SqlDataSource2"中SelectCommand="SELECT [Pro_name], [pro_ClassId] FROM [Pro_NameID]">DropDownList1变化是赋值
或设置DropDownList1为参数，根据参数联动
还有AJAX

Answer 8

DropDownList1启用autopostback貌似就解决了、楼主可以尝试

Answer 9

 ID="DropDownList2"  AutoPostBack="True" 

Answer 10

2个DropDownList的代码：
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
            onselectedindexchanged="DropDownList1_SelectedIndexChanged">
        </asp:DropDownList>
        
        <asp:DropDownList ID="DropDownList2" runat="server">
        </asp:DropDownList>DropDownList1的数据你是从数据库里读取的，DropDownList2的数据先不用绑定后台
 protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string value = this.DropDownList1.SelectedItem.Value.ToString();
 
                this.DropDownList2.Items.Clear();
        this.DropDownList2.Items.Add(new ListItem(value, value));//如果你是根据选择的数据再查询出一个集合的话，上面的就不用换下面的
this.DropDownList2.DataSource = dt;
        this.DropDownList2.DataTextField = "显示的字段";
        this.DropDownList2.DataValueField = "一般是ID";
        this.DropDownList2.DataBind();
    }

Answer 11

如果DropDownList1没有启用autopostback，还得启用

Answer 12

DropDownList1启用了autopostback，
DropDownList2取消了autopostback，
现在DropDownList2能根据DropDownList1的值来读取数据，
但是无论怎么选Response.Write(DropDownList2.SelectedItem.Text)  显示出来的值总是DropDownList2里面的第一项

Answer 13

Just SoSo
http://www.cnblogs.com/zhangyu028/articles/310568.html

Answer 14

问题解决了，我把SelectCommand="SELECT [Pro_name], [pro_ClassId] FROM [Pro_NameID]">
改成SelectCommand="SELECT [Pro_name] FROM [Pro_NameID]">
就可以了。
但还是不懂为什么？