如何使用DropDownList的SelectedIndexChanged事件

Question

我的网络表单中有两个DropDownList ，当我在第一个下拉列表中选择一个值时，我希望在第二个下拉列表中自动选择一个相关值。

这是我目前拥有的：

    <table>   
        <tr>
            <td>
                <asp:Label ID="lbmanu" runat="server" Text="Furniture Manufacturer : 
                   "></asp:Label>
            </td>
            <td>
                <asp:DropDownList ID="ddmanu" runat="server" 
                    DataSourceID="Sql_fur_model_manu"    
                    DataTextField="manufacturer" DataValueField="manufacturer" 
                    onselectedindexchanged="ddmanu_SelectedIndexChanged">
                </asp:DropDownList>
                <asp:SqlDataSource ID="Sql_fur_model_manu" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:conStr %>" 
                    SelectCommand="SELECT DISTINCT [manufacturer] FROM 
                     [furniture_manufacturer]">
                </asp:SqlDataSource>
            </td>
        </tr>
        <tr>
            <td>
                <asp:Label ID="lbtype" runat="server" Text="Furniture Type : 
                        "></asp:Label>
            </td>
            <td>
                <asp:DropDownList ID="ddtype" runat="server" AutoPostBack="True">
                   </asp:DropDownList>
            </td>
        </tr>
   </table>

背后的代码：

protected void ddmanu_SelectedIndexChanged(object sender, EventArgs e)
{
    string query = "select furniture from furniture_model where manufacturer='" + 
    ddmanu.SelectedValue.ToString() + "'";
    con.Open();
    cmd = new SqlCommand(query, con);
    DataTable dt = Select(query);
    cmd.ExecuteNonQuery();
    ddtype.DataSource = dt;
    ddtype.DataTextField = "manufacturer";
    ddtype.DataValueField = "furniture";
    ddtype.DataBind(); 
}

Answer 1

您应该将AutoPostBack =“ true”添加到DropDownList1

                <asp:DropDownList ID="ddmanu" runat="server" AutoPostBack="true"
                    DataSourceID="Sql_fur_model_manu"    
                    DataTextField="manufacturer" DataValueField="manufacturer" 
                    onselectedindexchanged="ddmanu_SelectedIndexChanged">
                </asp:DropDownList>

Answer 2

您可以在DropDownLists的SelectedIndexChanged事件中执行此操作的最基本方法。 检查此代码。

    <asp:DropDownList ID="DropDownList1" runat="server" onselectedindexchanged="DropDownList1_SelectedIndexChanged" Width="224px"
        AutoPostBack="True" AppendDataBoundItems="true">
    <asp:DropDownList ID="DropDownList2" runat="server"
        onselectedindexchanged="DropDownList2_SelectedIndexChanged">
    </asp:DropDownList> 


protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    //Load DropDownList2

}
protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{
    //Load DropDownList3
}

Answer 3

我认为这是罪魁祸首：

cmd = new SqlCommand(query, con);

DataTable dt = Select(query);

cmd.ExecuteNonQuery();

ddtype.DataSource = dt;

我不知道该代码应执行的操作，但是您似乎想为此创建一个SqlDataReader ，如此处和整个网络中所述，如果您搜索“ SqlCommand DropDownList DataSource”，则说明：

cmd = new SqlCommand(query, con);
ddtype.DataSource = cmd.ExecuteReader();

或者你可以创建一个DataTable作为解释在这里 ：

cmd = new SqlCommand(query, con);

SqlDataAdapter listQueryAdapter = new SqlDataAdapter(cmd);
DataTable listTable = new DataTable();
listQueryAdapter.Fill(listTable);

ddtype.DataSource = listTable;

Answer 4

使用下拉列表ddmanu AutoPostBack="true"将AutoPostBack属性设置为true 。