dropdownlist的二级连接无论怎么选择,都是显示第一个数据.为什么?
比如:第一个列表有 " 四川 河南 河北 "
第二个列表是根据第一个变化而变化
但是无论第一个选什么值,都是四川的城市 "成都 宜宾 绵阳 " 为什么呢?
代码如下:
<script language= "vb " runat= "server ">
Dim Myds As DataSet
Sub Page_Load(sender as object, e as Eventargs)
dim conn as new oledbconnection()
conn.connectionstring= "Provider=Microsoft.Jet.OLEDB.4.0; Data Source= " & server.MapPath( "../db/data.mdb ")
conn.open()
Dim strSql As String
strSql= "select * from category order by categoryid "
Dim MyoleAp As OleDbDataAdapter = New OleDbDataAdapter(strSql,conn)
Myds=New DataSet()
MyoleAp.Fill(Myds, "category ")
DropDownList1.DataSource=Myds.Tables( "category ")
DropDownList1.DataValueField= "categoryid "
DropDownList1.DataTextField= "category "
DropDownList1.DataBind()

strSql= "select * from sortsid order by sortsid "
MyoleAp.SelectCommand.CommandText=strSql
MyoleAp.Fill(Myds, "sortsid ")
DropDownList2.DataSource=Myds.Tables( "sortsid ")
DropDownList2.DataValueField= "sortsid "
DropDownList2.DataTextField= "sorts "
MyoleAp.Dispose()
conn.close()
End Sub



Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Myds.Tables( "sortsid ").DefaultView.RowFilter= "categoryid= ' " & DropDownList1.selectedvalue & " ' "
DropDownList2.DataBind()
End Sub
</script>
<略>
<form runat= "server " >
<asp:DropDownList ID= "DropDownList1 " OnSelectedIndexChanged= "DropDownList1_SelectedIndexChanged " AutoPostBack= "true " runat= "server " />
<asp:DropDownList ID= "DropDownList2 " runat= "server " />
</form>

[解决办法]
DropDownList1.DataSource = Myds.Tables( "category ")
DropDownList1.DataValueField = "categoryid "
DropDownList1.DataTextField = "category "
DropDownList1.DataBind()

这几句前后加上
If (Not IsPostBack) Then 和 End If
变为

If (Not IsPostBack) Then
DropDownList1.DataSource = Myds.Tables( "category ")
DropDownList1.DataValueField = "categoryid "
DropDownList1.DataTextField = "category "
DropDownList1.DataBind()
End If

防止提交返回时仍然重新载入DropDownList1的数据并默认将Value置0.
就行了.