c# - 在按钮上单击下拉列表以刷新

Question

我有两个下拉列表，一个用于州，另一个用于城市。此外，为了添加额外的城市，还有另一种形式，它会在新标签页中打开。

我想要的是，当我从新选项卡中为各自的州添加额外的城市时。我想刷新 State 下拉列表，这样当我从下拉列表中选择相应的 State 时，我可以获取添加的额外城市。

请看HTML代码:-

<tr>
    <td class="td">Location/State</td>
    <td>
        <asp: DropDownList CssClass="txtfld-popup" ID="ddlState" OnSelectedIndexChanged="ddlState_SelectedIndexChanged" runat="server" AutoPostBack="true"></asp:DropDownList>
        <asp:RequiredFieldValidator CssClass="error_msg" ID="RequiredFieldValidator1" ControlToValidate="ddlState" runat="server" ErrorMessage="Please enter State" InitialValue="--Select--" SetFocusOnError="true"></asp:RequiredFieldValidator>
    </td>
</tr>

有人建议使用 UpdatePanel 但我无法使用它。请帮忙

城市下拉列表的 HTML:

<tr>
                <td class="td">Location/City</td>
                <td>
                    <asp:DropDownList CssClass="txtfld-popup" ID="ddlCity" runat="server" AutoPostBack="true"></asp:DropDownList>
                    <a id="aExtraCity" href="AddCity.aspx" runat="server">Add City</a>
                    <asp:RequiredFieldValidator CssClass="error_msg" ID="reqLocation" ControlToValidate="ddlCity" runat="server" ErrorMessage="Please enter City" InitialValue="--Select--" SetFocusOnError="true"></asp:RequiredFieldValidator>

                </td>

另请参阅下拉列表背后的代码:-

public void LoadDropDowns()
{
    string country = "India";
    ddlCountry.SelectedValue = country;
    ddlCountry.Enabled = false;

    ddlMinExpYr.DataSource = Years;
    ddlMinExpYr.DataBind();
    ddlMaxExpYr.DataSource = Years;
    ddlMaxExpYr.DataBind();

    //populate states
    var states = _helper.GetStates(country);
    states.Insert(0, "--Select--");
    ddlState.DataSource = states;
    ddlState.DataBind();
}

AddCity 后面的代码:-

protected void btnAddDropDown_Click(object sender, EventArgs e)
{  

    using (SqlConnection con = new SqlConnection(constring))
    {
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.CommandText = "Add_CityforLocation";
        cmd.Parameters.Add("@ID", SqlDbType.VarChar).Value = 0;
        cmd.Parameters.Add("@CountryName", SqlDbType.VarChar).Value = "India";
        cmd.Parameters.Add("@StateName", SqlDbType.VarChar).Value = ddlState.SelectedItem.ToString();
        cmd.Parameters.Add("@CityName", SqlDbType.VarChar).Value = txtCity.Text.Trim();
        cmd.Connection = con;
        try
        {
            cmd.ExecuteNonQuery();
            // BindContrydropdown();
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);//You Can Haave Messagebox here
        }
        finally
        {
            con.Close();
        }
    }
    ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "ScriptKey", "alert('Your City has been Added.');window.location='Career_Job.aspx'; ", true);
}

Answer 1

可以通过实现长轮询或使用 SignalR 等框架作品来更新城市下拉列表，而无需从客户端触发任何事件。提出并回答了一个非常相似的问题here .

这是一个使用 SignalR 的 Web 表单示例。确保从 NuGet 下载并安装 Microsoft.AspNet.SignalR。

Startup.cs 更改

    using Microsoft.AspNet.SignalR;
    using Microsoft.Owin.Cors;
    using Owin;
    public partial class Startup {
    public void Configuration(IAppBuilder app)
    {
        // map signalr hubs
        app.Map("/city", map => {
                             map.UseCors(CorsOptions.AllowAll);
                             var config = new HubConfiguration() {
                                 EnableJSONP = true,
                                 EnableJavaScriptProxies = false
                             };

                             config.EnableDetailedErrors = true;


                             map.RunSignalR(config);
                         });

        ConfigureAuth(app);
    }
}

这是一个简单的 Hub，它将负责更新所有订阅的客户端，添加任何新城市。

using System.Threading.Tasks;
using Microsoft.AspNet.SignalR;

public class CityHub : Hub {
    // will be called from client side to send new city 
    // data to the client with drop down list
    public Task SendNewCity(string cityName) 
    {
        // dynamically typed method to update all clients
        return Clients.All.NewCityNotification(cityName);

    }

}

这是一个帮助程序 js 脚本，用于创建与集线器的连接。请注意，这段代码来自另一个示例，我也包含了许可证。只需在您的解决方案中的某处创建一个 JavaScript 文件并添加此脚本。您将在客户端上使用它。 我在 ~/Scripts/app.js 下添加了这个

~/Scripts/app.js

/*!
 * ASP.NET SignalR JavaScript Library v2.0.0
 * http://signalr.net/
 *
 * Copyright Microsoft Open Technologies, Inc. All rights reserved.
 * Licensed under the Apache 2.0
 * https://github.com/SignalR/SignalR/blob/master/LICENSE.md
 *
 */

/// <reference path="..\..\SignalR.Client.JS\Scripts\jquery-1.6.4.js" />
/// <reference path="jquery.signalR.js" />
(function ($, window, undefined) {
    /// <param name="$" type="jQuery" />
    "use strict";

    if (typeof ($.signalR) !== "function") {
        throw new Error("SignalR: SignalR is not loaded. Please ensure jquery.signalR-x.js is referenced before ~/signalr/js.");
    }

    var signalR = $.signalR;

    function makeProxyCallback(hub, callback) {
        return function () {
            // Call the client hub method
            callback.apply(hub, $.makeArray(arguments));
        };
    }

    function registerHubProxies(instance, shouldSubscribe) {
        var key, hub, memberKey, memberValue, subscriptionMethod;

        for (key in instance) {
            if (instance.hasOwnProperty(key)) {
                hub = instance[key];

                if (!(hub.hubName)) {
                    // Not a client hub
                    continue;
                }

                if (shouldSubscribe) {
                    // We want to subscribe to the hub events
                    subscriptionMethod = hub.on;
                } else {
                    // We want to unsubscribe from the hub events
                    subscriptionMethod = hub.off;
                }

                // Loop through all members on the hub and find client hub functions to subscribe/unsubscribe
                for (memberKey in hub.client) {
                    if (hub.client.hasOwnProperty(memberKey)) {
                        memberValue = hub.client[memberKey];

                        if (!$.isFunction(memberValue)) {
                            // Not a client hub function
                            continue;
                        }

                        subscriptionMethod.call(hub, memberKey, makeProxyCallback(hub, memberValue));
                    }
                }
            }
        }
    }

    $.hubConnection.prototype.createHubProxies = function () {
        var proxies = {};
        this.starting(function () {
            // Register the hub proxies as subscribed
            // (instance, shouldSubscribe)
            registerHubProxies(proxies, true);

            this._registerSubscribedHubs();
        }).disconnected(function () {
            // Unsubscribe all hub proxies when we "disconnect".  This is to ensure that we do not re-add functional call backs.
            // (instance, shouldSubscribe)
            registerHubProxies(proxies, false);
        });

        proxies.cityHub = this.createHubProxy('cityHub');
        proxies.cityHub.client = {};
        proxies.cityHub.server = {

            sendNewCity: function (message) {
                /// <summary>Calls the Send method on the server-side ChatHub hub.&#10;Returns a jQuery.Deferred() promise.</summary>
                /// <param name=\"message\" type=\"String\">Server side type is System.String</param>
                return proxies.cityHub.invoke.apply(proxies.cityHub, $.merge(["SendNewCity"], $.makeArray(arguments)));
            }
        };

        return proxies;
    };

    signalR.hub = $.hubConnection("/signalr", { useDefaultPath: false });
    $.extend(signalR, signalR.hub.createHubProxies());

}(window.jQuery, window));

这是一个简单的页面，您可以在其中输入一个文本和一个用于添加新城市的按钮。请注意，您将需要 jquery、jquery.signalR 和上面的脚本 (/Scripts/app.js)。

AddNewCity.aspx

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script src="../../Scripts/jquery-1.10.2.min.js"></script>
    <script src="../../Scripts/jquery.signalR-2.2.0.min.js"></script>
    <script src="../../Scripts/app.js"></script>

    <script>
        $(function () {
            var cityHub = $.connection.cityHub;
            $.connection.hub.url = "/city";
            $.connection.hub.logging = true;

            $.connection.hub.start().done(function () {
                $("#addCity").click(function () {
                    cityHub.server.sendNewCity($("#cityName").val())
                                        .fail(function (err) {
                                            alert(err);
                                        });
                    $("#text").val("").focus();
                });
            });
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <input id ="cityName" type="text" placeholder="City name"/>
        <input id="addCity" type="button" value="Add City"/>
    </div>
    </form>
</body>
</html>

这是一个单独的页面，您的城市下拉列表存在于其中。一旦您从“添加城市”页面添加新城市，这个单独的页面将自动更新。

CityDropDownList.aspx

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script src="../../Scripts/jquery-1.10.2.min.js"></script>
    <script src="../../Scripts/jquery.signalR-2.2.0.min.js"></script>
    <script src="../../Scripts/app.js"></script>
    <script>
        $(function () {
            var cityHub = $.connection.cityHub;
            $.connection.hub.url = "/city";
            $.connection.hub.logging = true;

            cityHub.client.newCityNotification = newCityNotification;

            $.connection.hub.start().done(function () {
                
            });

            function newCityNotification(city) {
                $("#cityddl").append($(getCityOptionItem(city)));
            }


            function getCityOptionItem(city) {
                return "<option>" + city + "</option>";
            }

        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <select id="cityddl">
            <option id="0">Existing City</option>
        </select>
    </div>
    </form>
</body>
</html>

我自己测试过，似乎一切正常。您应该以 2 个单独的页面结束，AddNewCity.aspx 和 CityDropDownList.aspx。从 AddNewCity.aspx 添加新城市后，该值将发送到 CityDropDownList.aspx 并使用新城市更新下拉列表。