Simple JSON handler for ASP.NET to implement AJAX functionality

• Download SampleJSONWeb - 225.34 KB

Introduction

This article described how to use AJAX functionality using the popular JavaScript library (jQuery) with a minimal amount of code without using ASP.NET AJAX tool kit.

This example has two drop down controls whereas customer and customer description. Customer description will be loaded when customer drop down change without reloading the entire page.

Using the code

• Jquary library files need to be included to the project as shown above.

These are the library files

• jquery-1.4.1-vsdoc.js,jquery-1.4.1.js,
• query-1.4.1.min.js,
• jquery-1.5.2.min.js,
• jquery-ui-1.8.11.custom.min.js

var ajax = {

    setDebugMode: function(){
        this.debugMode = true;
    },

    get: function (requestUrl, data, loaderImageId, onSuccess, onComplete) {

        if (loaderImageId) {
            $("#" + loaderImageId).css('display', 'inline');
        }

        var completeFunction = function () {
            if (onComplete) {
                onComplete();
            }
            if (loaderImageId) {
                $("#" + loaderImageId).css('display', 'none');
            }
        };

        $.ajax({
            type: "GET",
            url: requestUrl,
            data: data,
            context: this,
            success: function (response) {
                onSuccess(response);
                completeFunction();
            },
            error: function (response) {
                alert("Ajax Request Failed");
                this.showError(response);
                completeFunction();
            }
        });
    },

    post: function (requestUrl, data, loaderImageId, onSuccess, onComplete) {

        if (loaderImageId) {
            $("#" + loaderImageId).css('display', 'inline');
        }

        var completeFunction = function () {
            if (onComplete) {
                onComplete();
            }
            if (loaderImageId) {
                $("#" + loaderImageId).css('display', 'none');
            }
        };

        $.ajax({
            type: "POST",
            url: requestUrl,
            context: this,
            data: data,
            success: function (response) {
                onSuccess(response);
                completeFunction();
            },
            error: function (response) {
                alert("Ajax Request Failed");
                this.showError(response);
                completeFunction();
            }
        });
    },

    showError: function(requestObject){
        if (this.debugMode){
            alert(requestObject.responseText);
        }
    }
};

ASPX Page(SampleAjax.aspx)

Include the java script as below

<script type="text/javascript" src='<%= this.ResolveUrl("~/Scripts/jquery-1.5.2.min.js")%>' ></script>
<script type="text/javascript" src='<%= this.ResolveUrl("~/Scripts/jquery-ui-1.8.11.custom.min.js")%>' ></script>
<script type="text/javascript" src='<%= this.ResolveUrl("~/Scripts/sample_ajax.js")%>' ></script>         

Write Java script to call customer descriptions when customer drop down change

     <script type="text/javascript">
     <% if (SampleJSONWeb.ConfigurationData.DebugMode){ %>
                    ajax.setDebugMode();
            <%} %>
    $(document).ready(function () 
    {
        $("#<%= customerDropDown.ClientID %>").change(function () 
        {
                var customerTypeId = $('#<%= customerDropDown.ClientID %>').val();
                ajax.get('<%= this.ResolveUrl("~/LoadCustomerDescriptions.ashx")%>',
                    { 'customerTypeId': customerTypeId },
                    'CustomerDescriptionsLoader',
                        function (response) 
                        {
                            $('#<%= customerDescriptionDropDown.ClientID %> option').remove();
                            for (var i = 0; i < response.Data.length; i++) 
                            {
                                $('#<%= customerDescriptionDropDown.ClientID %>').append(getOptionString(response.Data[i]));
                            }
                        }
                    );
            });
    
    
        function getOptionString(dataElement)
        {
          return "<option value='"+dataElement.Id+"' >"+dataElement.Name+"</option>";
        }
    });

</script>     

LoadCustomerDescriptions.ashx will be invoked by above java script.

public class LoadCustomerDescriptions : JsonRequestHandler
 {
     public override void ProcessRequest(HttpContext context)
     {
         string customerTypeId = context.Request.QueryString["customerTypeId"].ToString();

         //load data
         GetData getData = new GetData();
         IList<ReferenceData> data = getData.GetCustomerescriptions(customerTypeId);

         //Insert an empty row as the first row
         data.Insert(0, new ReferenceData(string.Empty, string.Empty));

         //return as JSON result
         Dictionary<string, string> response = new Dictionary<string, string>();
         response.Add("Data", GetJsonCollection<ReferenceData>(data));
         SetResponse(context, response);
     }
 }

The above method get the data from back end and send back as JSON format. JSON handler has the implementation to manage JSON data as below

using System;
using System.Collections.Generic;
using System.Web;
using System.Text;
using System.Reflection;
using System.Web.SessionState;

namespace SampleJSONWeb
{
    public abstract class JsonRequestHandler : IHttpHandler, IRequiresSessionState
    {

        public abstract void ProcessRequest(HttpContext context);

        protected void SetResponse(HttpContext context, string jsonResponse)
        {
            context.Response.Cache.SetExpires(DateTime.Now);
            context.Response.ContentType = "application/json";
            context.Response.Write(jsonResponse);
            context.Response.End();
        }

        protected void SetResponse(HttpContext context, Dictionary<string, string> attributes)
        {
            SetResponse(context, GetJsonObject(attributes));
        }

        protected void SetResponse<T>(HttpContext context, T obj)
        {
            SetResponse(context, GetJsonObject<T>(obj));
        }

        protected T CreateObjectFromRequest<T>(HttpContext context) where T: new()
        {
            T ob = new T();
            PropertyInfo[] properties = typeof(T).GetProperties();
            foreach (PropertyInfo property in properties)
            {
                string value = context.Request.Params[property.Name];
                if (value == null)
                {
                    continue;
                }

                if (property.PropertyType != typeof(string) && value == string.Empty)
                {
                    continue;
                }

                object convertedValue = Convert.ChangeType(value, property.PropertyType);
                if (convertedValue == null)
                {
                    continue;
                }

                property.SetValue(ob, convertedValue, null);
            }
            return ob;
        }

        protected string GetJsonObject(Dictionary<string, string> attributes)
        {
            StringBuilder jsonBuilder = new StringBuilder();
            jsonBuilder.Append("{");
            bool firstTime = true;
            foreach (string key in attributes.Keys)
            {
                if (!firstTime)
                {
                    jsonBuilder.Append(",");
                }

                string name = key;
                object value = attributes[key];
                jsonBuilder.Append("\"" + name + "\":" + value.ToString());
                firstTime = false;
            }
            jsonBuilder.Append("}");
            return jsonBuilder.ToString();
        }

        protected string GetJsonCollection<T>(IEnumerable<T> collection)
        {
            StringBuilder jsonBuilder = new StringBuilder();
            jsonBuilder.Append("[");

            bool first = true;
            foreach (T item in collection)
            {
                if (!first)
                {
                    jsonBuilder.Append(",");
                }
                jsonBuilder.Append(GetJsonObject<T>(item));
                first = false;
            }

            jsonBuilder.Append("]");
            return jsonBuilder.ToString();
        }

        protected string GetJsonObject<T>(T obj)
        {
            PropertyInfo[] properties = typeof(T).GetProperties();
            StringBuilder jsonBuilder = new StringBuilder();
            jsonBuilder.Append("{");
            bool firstTime = true;
            foreach (PropertyInfo property in properties)
            {
                if (!firstTime)
                {
                    jsonBuilder.Append(",");
                }

                string name = property.Name;
                object value = property.GetValue(obj, null);
                jsonBuilder.Append("\"" + name + "\":\"" + value.ToString() + "\"");
                firstTime = false;
            }
            jsonBuilder.Append("}");
            return jsonBuilder.ToString();
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}