C# DropDownList OnSelectedIndexChanged未触发

我的主要目的是，根据ddlMedicalName选择填充ddlCity DropDownList。但我的主要问题是，尽管我尝试了几乎所有的解决方案，但我还是无法让它改变

我知道，关于这个问题有很多问题和答案，我已经尝试过almos的每一个问题，但仍然不起作用。我已经了解到EnableStateView=True不仅应该应用于DropDownList，还应该应用于整个页面，因此我在Web.Config中添加了以下代码：

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

这里是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>

梅迪齐尼什雷东酒店
区域
斯塔特
-产品-
-产品-
-产品-

如有任何帮助，将不胜感激更改：

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{

致：

或者相反：

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

致：

您当前指向名为“…\u SelectedIndexChanged”的句柄，并提供“…\u OnSelectedIndexChanged”。

更改：

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{

致：

或者相反：

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

致：

---

您当前指向名为“…\u SelectedIndexChanged”的句柄，并提供“…\u OnSelectedIndexChanged”。

我测试了您的代码。以下是我目前发现的-

ddlMedicalName\u OnSelectedIndexChanged事件已正确触发

ddlMedicalName.SelectedValue是一个字符串值字符串不是ddlCity的有效数据源。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： 以下是我如何测试-

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)
{

}

受保护的无效页面加载（对象发送方，事件参数e）
{
如果（！Page.IsPostBack）
{
ddlBind（）；
}
}
公营医疗
{
公共整数{get；set；}
公共字符串MedicalName{get；set；}
public int CityFK{get；set；}
}
公营城市
{
public int CityID{get；set；}
公共字符串CityName{get；set；}
}
受保护的void ddlBind（）
{
var medicals=新列表（）
{
新医学{MedicalID=1，MedicalName=“一”，CityFK=11}，
新医学{MedicalID=2，MedicalName=“2”，CityFK=22}，
新医学{MedicalID=3，MedicalName=“三”，CityFK=33}，
新医学{MedicalID=4，MedicalName=“Four”，CityFK=44}，
};
ddlMedicalName.DataSource=medicals；
ddlMedicalName.DataTextField=“medicalname”；
ddlMedicalName.DataValueField=“cityfk”；
ddlMedicalName.DataBind（）；
}
受保护的无效ddlMedicalName_OnSelectedIndexChanged（对象发送方，事件参数e）
{
var cities=新列表（）
{
新城{CityID=11，CityName=“城市一号”}，
新城{CityID=22，CityName=“City Two”}，
新城{CityID=33，CityName=“城市三号”}，
新城{CityID=44，CityName=“City Four”}，
};
int slc=Convert.ToInt32（ddlMedicalName.SelectedItem.Value）；
var订单=来自城市的订单
其中order.CityID==slc
选择新的{order.CityID，order.CityName}；
var lstsrc=orders.ToList（）；
ddlCity.DataSource=lstsrc；
ddlCity.DataTextField=“CityName”；
ddlCity.DataValueField=“CityID”；
ddlCity.DataBind（）；
}
受保护的无效DDL区域\u SelectedIndexChanged（对象发送方，事件参数e）
{
}
受保护的void ddlCity\u SelectedIndexChanged（对象发送方，事件参数e）
{
}
受保护的无效搜索按钮\u单击（对象发送者，事件参数e）
{
}

我测试了你的代码。以下是我目前发现的-

ddlMedicalName\u OnSelectedIndexChanged事件已正确触发

ddlMedicalName.SelectedValue是一个字符串值字符串不是ddlCity的有效数据源。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： 以下是我如何测试-

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)
{

}

受保护的无效页面加载（对象发送方，事件参数e）
{
如果（！Page.IsPostBack）
{
ddlBind（）；
}
}
公营医疗
{
公共整数{get；set；}
公共字符串MedicalName{get；set；}
public int CityFK{get；set；}
}
公营城市
{
public int CityID{get；set；}
公共字符串CityName{get；set；}
}
受保护的void ddlBind（）
{
var medicals=新列表（）
{
新医学{MedicalID=1，MedicalName=“一”，CityFK=11}，
新医学{MedicalID=2，MedicalName=“2”，CityFK=22}，
新医学{MedicalID=3，MedicalName=“三”，CityFK=33}，
新医学{MedicalID=4，MedicalName=“Four”，CityFK=44}，
};
ddlMedicalName.DataSource=medicals；
ddlMedicalName.DataTextField=“medicalname”；
ddlMedicalName.DataValueField=“cityfk”；
ddlMedicalName.DataBind（）；
}
受保护的无效ddlMedicalName_OnSelectedIndexChanged（对象发送方，事件参数e）
{
var cities=新列表（）
{
新城{CityID=11，CityName=“城市一号”}，
新城{CityID=22，CityName=“City Two”}，
新城{CityID=33，CityName=“城市三号”}，
新城{CityID=44，CityName=“City Four”}，
};
int slc=Convert.ToInt32（ddlMedicalName.SelectedItem.Value）；
var订单=来自城市的订单
其中order.CityID==slc
选择新的{order.CityID，order.CityName}；
var lstsrc=orders.ToList（）；
ddlCity.DataSource=lstsrc；
ddlCity.DataTextField=“CityName”；
ddlCity.DataValueField=“CityID”；
ddlCity.DataBind（）；
}
受保护的无效DDL区域\u SelectedIndexChanged（对象发送方，事件参数e）
{
}
受保护的void ddlCity\u SelectedIndexChanged（对象发送方，事件参数e）
{
}
受保护的无效搜索按钮\u单击（对象发送者，事件参数e）
{
}

请根据我的建议进行更改并尝试。您必须删除下面的行

ddlMedicalName.DataValueField = "cityfk";

或

将cityfk更改为medicalname，然后重试

ddlMedicalName.DataValueField = "medicalname";

---

请根据我的建议更改并尝试。您必须删除下面的行

ddlMedicalName.DataValueField = "cityfk";

或

将cityfk更改为medicalname，然后重试

ddlMedicalName.DataValueField = "medicalname";

---

其他下拉菜单是否触发了事件？您