DropDownList OnSelectedIndexChanged没有触发

Question

我的主要目的是根据ddlMedicalName选择填充ddlCity DropDownList。 但是我的主要问题是，尽管我尝试了该问题的几乎所有解决方案，但都无法触发ddlMedicalName_OnSelectedIndexChanged。

我知道，关于这个问题有很多疑问和答案，我已经尝试了每个人的almos，但仍然行不通。 我已经阅读到EnableStateView = True不仅应应用于DropDownList，而且还应应用于整个页面，因此，我将以下代码添加到Web.Config中：

 <system.web>
<pages styleSheetTheme="MainTheme" enableViewState="true"/>

这是我的代码背后：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;



namespace MedicalBootStrap
{

public partial class WebForm1 : System.Web.UI.Page
{
    Entity.medicaldbEntities context = new Entity.medicaldbEntities();

    protected void Page_Load(object sender, EventArgs e)
    {

        if (!Page.IsPostBack)
        {
            ddlBind();
        }

    }

    protected void ddlBind()
    {

        var orders = from order in context.Medicals

                     select new { order.MedicalID, order.medicalName, order.CityFK };

        var lstsrc = orders.ToList();

        ddlMedicalName.DataSource = lstsrc;
        ddlMedicalName.DataTextField = "medicalname";
        ddlMedicalName.DataValueField = "cityfk";

        ddlMedicalName.DataBind();

    }

    protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
    {

          int slc = Convert.ToInt32(ddlMedicalName.SelectedItem.Value);

        var orders = from order in context.Cities
                     where order.CityID == slc
                     select new { order.CityID, order.CityName};

        var lstsrc = orders.ToList();

        ddlMedicalName.DataSource = lstsrc;
        ddlMedicalName.DataTextField = "medicalname";
        ddlMedicalName.DataValueField = "cityfk";

        ddlMedicalName.DataBind();
    }

    protected void ddlRegion_SelectedIndexChanged(object sender, EventArgs e)
    {

    }

    protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
    {

    }

    protected void SearchButton_Click(object sender, EventArgs e)
    {

    }   
 }
}

这是aspx：

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="MedizinischeLeistungen.aspx.cs" Inherits="MedicalBootStrap.WebForm1" EnableViewState="true" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server" EnableViewState="true">
<table id="SearchTable">
<tr>
<td>Medizinische Leistung</td>
<td>Region</td>
<td>Stadt</td>
</tr>
<tr id="SearchDropDown">

<td>
    <asp:DropDownList ID="ddlMedicalName" runat="server" EnableViewState="true" 
        AutoPostBack="True"  AppendDataBoundItems="true"
    OnSelectedIndexChanged="ddlMedicalName_OnSelectedIndexChanged">
    <asp:ListItem Value="" Selected="True"> - Product - </asp:ListItem>
    </asp:DropDownList>
</td>

<td>
    <asp:DropDownList ID="ddlRegion" runat="server" AutoPostBack="true" EnableViewState="true"
onselectedindexchanged="ddlRegion_SelectedIndexChanged">
<asp:ListItem Value="" Selected="True"> - Product - </asp:ListItem>
    </asp:DropDownList>
</td>
<td>
    <asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true" EnableViewState="true"
onselectedindexchanged="ddlCity_SelectedIndexChanged">
<asp:ListItem Value="" Selected="True"> - Product - </asp:ListItem>
    </asp:DropDownList>
</td>
<td>
    <asp:Button ID="SearchButton" runat="server" Text="Suche" onclick="SearchButton_Click" />

</td>
</tr>
</table>




</asp:Content>

任何帮助，将不胜感激

Answer 1

我测试了您的代码。 这是我到目前为止发现的-

正确触发了ddlMedicalName_OnSelectedIndexChanged事件。

ddlMedicalName.SelectedValue是一个字符串值； 字符串不是 ddlCity.DataSource 的有效数据源

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{
    // Problem is the following 3 line of codes.
    ddlCity.DataSource = ddlMedicalName.SelectedValue; 
    ddlCity.DataTextField = ddlMedicalName.SelectedValue;
    ddlCity.DataValueField = ddlMedicalName.SelectedValue;

    ddlCity.DataBind();
}

更新：

这是我的测试方式-

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        ddlBind();
    }
}

public class Medical
{
    public int MedicalID { get; set; }
    public string MedicalName { get; set; }
    public int CityFK { get; set; }
}

public class City
{
    public int CityID { get; set; }
    public string CityName { get; set; }
}

protected void ddlBind()
{
    var medicals = new List<Medical>()
    {
        new Medical {MedicalID = 1, MedicalName = "One", CityFK = 11},
        new Medical {MedicalID = 2, MedicalName = "Two", CityFK = 22},
        new Medical {MedicalID = 3, MedicalName = "Three", CityFK = 33},
        new Medical {MedicalID = 4, MedicalName = "Four", CityFK = 44},
    };

    ddlMedicalName.DataSource = medicals;
    ddlMedicalName.DataTextField = "medicalname";
    ddlMedicalName.DataValueField = "cityfk";

    ddlMedicalName.DataBind();

}

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{
    var cities = new List<City>()
    {
        new City {CityID = 11, CityName = "City One"},
        new City {CityID = 22, CityName = "City Two"},
        new City {CityID = 33, CityName = "City Three"},
        new City {CityID = 44, CityName = "City Four"},
    };

    int slc = Convert.ToInt32(ddlMedicalName.SelectedItem.Value);

    var orders = from order in cities
                    where order.CityID == slc
                    select new { order.CityID, order.CityName };

    var lstsrc = orders.ToList();

    ddlCity.DataSource = lstsrc;
    ddlCity.DataTextField = "CityName";
    ddlCity.DataValueField = "CityID";

    ddlCity.DataBind();
}

protected void ddlRegion_SelectedIndexChanged(object sender, EventArgs e)
{

}

protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
{

}

protected void SearchButton_Click(object sender, EventArgs e)
{

}

Answer 2

请按照我的建议更改并尝试。您必须删除以下行

ddlMedicalName.DataValueField = "cityfk";

要么

将cityfk更改为medicalname并尝试。

ddlMedicalName.DataValueField = "medicalname";

Answer 3

更改：

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{

至：

protected void ddlMedicalName_SelectedIndexChanged(object sender, EventArgs e)
{

或相反：

<asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true" EnableViewState="true" onselectedindexchanged="ddlCity_SelectedIndexChanged">

至：

<asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true"  EnableViewState="true" onselectedindexchanged="ddlCity_OnSelectedIndexChanged">

您当前指向的是名为“ ..._ SelectedIndexChanged”的句柄，并提供了“ ..._ OnSelectedIndexChanged”。