为什么asp：DropDownList不响应后台代码

Question

我有以下ASP下拉列表：

<asp:DropDownList ClientIDMode="Static" ID="ddlMain" name="searchPhys" style="width: 365px;" class="default" runat="server" AppendDataBoundItems="true">
        <asp:ListItem Text="BY PHYSICIAN" Value="0" Selected="True" />
        <asp:ListItem Text="BY LOCATION" Value="1" />
        <asp:ListItem Text="BY SPECIALTY" Value="2" />
</asp:DropDownList>
<br /><br />
<asp:DropDownList ClientIDMode="Static" ID="ddlDrillDown" name="searchPhys" style="width: 365px;" class="default" runat="server" AppendDataBoundItems="true">
</asp:DropDownList>

我正在尝试使其具有交互性，如果更改了第一个选择选项，则第二个也将根据第一个选择选项的选择进行更改。

我的C＃代码如下所示：

public partial class test : System.Web.UI.Page
{
    String cString;
    SqlConnection Conn;
    protected void Page_Load(object sender, EventArgs e) {

    PopulatePhysician();
    //PopulateSpecialty();
    //PopulateLocation();

    }


    public void PopulatePhysician() {
        SqlCommand cmd = new SqlCommand("getPhysicians", new SqlConnection(ConfigurationManager.AppSettings["ConnString"]));
        //cmd.CommandType = Data.CommandType.StoredProcedure
        cmd.Connection.Open();

        SqlDataReader ddlValues = default(SqlDataReader);
        ddlValues = cmd.ExecuteReader();

        //if (!IsPostBack) {
            ddlDrillDown.DataSource = ddlValues;
            ddlDrillDown.DataValueField = "content_id";
            ddlDrillDown.DataTextField = "content_title";
            ddlDrillDown.DataBind();
            //set the default value for the drop down
            ListItem Item = new ListItem();
            Item.Text = "Select a Physician's Name";
            Item.Value = "0";
            //Item.Selected = True
            ddlDrillDown.Items.Insert(0, Item);
        //}
    cmd.Connection.Close();
    cmd.Connection.Dispose();
    }

    public void PopulateSpecialty() {
        SqlCommand cmd = new SqlCommand("getSpecialties", new SqlConnection(ConfigurationManager.AppSettings["ConnString"]));
        cmd.Connection.Open();

        SqlDataReader ddlValues = default(SqlDataReader);
        ddlValues = cmd.ExecuteReader();

        //if (!IsPostBack) {
            ddlDrillDown.DataSource = ddlValues;
            ddlDrillDown.DataValueField = "content_id";
            ddlDrillDown.DataTextField = "content_title";
            ddlDrillDown.DataBind();
            //set the default value for the drop down
            ListItem Item = new ListItem();
            Item.Text = "Select a Specialty";
            Item.Value = "0";
            ddlDrillDown.Items.Insert(0, Item);
        //}
        cmd.Connection.Close();
        cmd.Connection.Dispose();
    }

    public void PopulateLocation() {
        SqlCommand cmd = new SqlCommand("getLocations", new SqlConnection(ConfigurationManager.AppSettings["ConnString"]));
        cmd.Connection.Open();

        SqlDataReader ddlValues = default(SqlDataReader);
        ddlValues = cmd.ExecuteReader();

        //if (!IsPostBack) {
            ddlDrillDown.DataSource = ddlValues;
            ddlDrillDown.DataValueField = "content_id";
            ddlDrillDown.DataTextField = "content_title";
            ddlDrillDown.DataBind();

            //set the default value for the drop down
            ListItem Item = new ListItem();
            Item.Text = "Select a Location";
            Item.Value = "0";
            ddlDrillDown.Items.Insert(0, Item);
        cmd.Connection.Close();
        cmd.Connection.Dispose();
        //}
    }

    public void ddlMain_SelectedIndexChanged(object sender, System.EventArgs e) {
        switch(ddlMain.SelectedItem.Value) {
            case "0":
                PopulatePhysician();
                break;
            case "1":
                PopulateLocation();
                break;
            case "2":
                PopulateSpecialty();
                break;
        }
    }
}

首次加载页面时， PopulatePhysician(); 通过填充选择选项，效果很好。 但是，当我调用SelectedIndexChanged()函数时，什么也没发生。

我该如何解决？ case陈述正确吗？

Answer 1

在下拉列表中需要AutoPostback=true

<asp:DropDownList AutoPostback="true" ClientIDMode="Static" ID="ddlMain" name="searchPhys" style="width: 365px;" class="default" runat="server" AppendDataBoundItems="true">

Answer 2

您尚未将任何委托添加到SelectedIndexChanged事件。

将OnSelectedIndexChanged添加到asp：DropDownList标记中的参数中，如下所示：

<asp:DropDownList ClientIDMode="Static" OnSelectedIndexChanged="ddlMain_SelectedIndexChanged" ID="ddlMain" name="searchPhys" style="width: 365px;" class="default" runat="server" AppendDataBoundItems="true"  >

编辑

我只是注意到您实际上实际上也缺少AutoPostBack事件-应该将其设置为true ，因为在不提交表单的情况下更新选择不会触发回发事件，除非AutoPostBack设置为true。

Answer 3

从函数中删除If（！IsPostBack）子句。 检查页面加载中的内容，而不检查每个单独的功能中的内容。