根据另一个下拉列表ID填充下拉列表时出错

Question

I have two dropdown lists and the second is populated based on the selected value of the first. This is how i had my second dropdown list populated but it wasn't filling based on the selected item in the first which lead me to change how i am filling it.

Before:

<asp:DropDownList ID="RootDropDown" runat="server" AutoPostBack="True" DataSourceID="FirstChild" DataTextField="DisplayName" DataValueField="ID"></asp:DropDownList>
        <asp:SqlDataSource ID="FirstChild" runat="server" ConnectionString="<%$ ConnectionStrings:MyConnection %>" SelectCommand="SELECT e.DisplayName,  e.ID , e.GUID
FROM SomeTable e
INNER JOIN TabletoTableMap em
ON e.ID = em.OtherTableID
WHERE em.SomeTableID = 9"+ ></asp:SqlDataSource>

After:

<asp:DropDownList ID="RootDropDown" runat="server" AutoPostBack="True" DataSourceID="FirstChild" DataTextField="DisplayName" DataValueField="ID" OnSelectedIndexChanged="Child"></asp:DropDownList>

Child Method:

protected void Child(object sender, EventArgs e)
    {
        String strConnection = "Data Source=.;Initial Catalog=ALE;Integrated Security=True";
        int RootID = Convert.ToInt32(CourseDropDown.SelectedValue);
        System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(strConnection);
        con.Open();
        System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand("SELECT e.DisplayName,  e.ID , e.GUID FROM SomeTable e INNER JOIN TabletoTableMap em ON e.ID = em.OtherTableID WHERE em.SomeTableID="+RootID, con);
        System.Data.SqlClient.SqlDataAdapter da = new System.Data.SqlClient.SqlDataAdapter(cmd);
        System.Data.DataSet ds = new System.Data.DataSet();
        da.Fill(ds);
        con.Close();
        RootElementDropDown.DataSourceID = "FirstChild";
        RootElementDropDown.DataTextField = "DisplayName";
        RootElementDropDown.DataValueField = "ID";
        RootElementDropDown.DataBind();
    }

Error:

The DataSourceID of 'RootDropDown' must be the ID of a control of type IDataSource.  A control with ID 'FirstChild' could not be found.

Answer 1

尝试设置

DataMember as what you want