JQuery ajax get returns null

Virendra Maurya

8y5.2k.NET

// THIS IS MY JAVA SCRIPT CODE 

"text/javascript">  
        function getAllMessages() {  
            $.ajax({  
                url: "TestService.asmx/GetAllMessages",  
                dataType: "json",  
                method: "GET",  
                contentType: "application/json",  
                success: onSuccess,  
                error: function (err) {  
                    console.log(err);  
                }  
            });  
        }  
  
        function onSuccess(data) {  
            console.log(data);  
            var messageTable = $("#messages tbody");  
            alert(data);  
            $(data).each(function (index, msg) {  
                var apnString = "" + msg.ID + "" + msg.Email + "" + msg.Message + "" + msg.TimeStamp + "";  
                messageTable.append(apnString);  
            });  
        }  
      
// WebMethod Code

SQLHelper clSQLHelper = new SQLHelper();
[System.Web.Script.Services.ScriptMethod(UseHttpGet = true, ResponseFormat = System.Web.Script.Services.ResponseFormat.Json)]
[WebMethod]
public void GetAllMessages()
{
List listMsg = new List();
DataTable dtMsg = clSQLHelper.PGSQLExecuteReader("get_all_messages", new List(), "Messages");
if (dtMsg != null && dtMsg.Rows.Count > 0)
{
foreach (DataRow dr in dtMsg.Rows)
{
Messages Msg = new Messages();
Msg.ID = Convert.ToInt32(dr["auto_id"]);
Msg.Email = dr["email_id"].ToString();
Msg.Message = dr["message"].ToString();
Msg.TimeStamp = Convert.ToDateTime(dr["created_on"], new CultureInfo("en-IN"));
listMsg.Add(Msg);
}
JavaScriptSerializer js = new JavaScriptSerializer();
Context.Response.Write(js.Serialize(listMsg));
}
}

Inside success callbak function, data value is null.

5 Replies

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Virendra Maurya8y ago
I have modified my return value to

JavaScriptSerializer js = new JavaScriptSerializer();
return js.Serialize(listMsg);

debug window does not show the response status

I am trying this article

https://www.c-sharpcorner.com/blogs/how-to-insert-and-retrieve-data-using-jquery-ajax-in-asp-net
Aakash Maurya8y ago
Hi Verendra,

I guess the problem is your web method is return type is "VOID". That is creating a problem. Try removing VOID and put proper return type.

I guess you have followed this example https://www.c-sharpcorner.com/article/return-json-response-from-webservice-in-Asp-Net/

But this example is printing the string on the browser page.

You can also make use following line to return the response.
string response = Newtonsoft.Json.JsonConvert.SerializeObject(new { resData });
return response;
This code is working fine for me. Let me know if this doesn't work for you. Also make sure that your return type of your web method should be String.
Virendra Maurya8y ago
My web method returns

[{"ID":48,"Email":"[email protected]","Message":"hj","TimeStamp":"\/Date(1501759273648)\/"},{"ID":60,"Email":"[email protected]","Message":"hi","TimeStamp":"\/Date(1528439285403)\/"}]

In front of web service it shows only time [3ms] in debugger while TestForm.aspx shows [HTTP/1.1 200 OK 7662ms].

in cosole.log i m getting this
GET XHR http://localhost:3317/TestService.asmx/GetAllMessages                                       [2ms]
null                                                                                                                    TestForm.aspx : 24:13
POST http://localhost:3317/TestForm.aspx                                            [HTTP/1.1 200 OK 138ms]
Sai Kumar Koona8y ago
can u add below code in your server-side code before writing output to the context?
context.Response.ContentType = "application/json";
Aakash Maurya8y ago
Have you checked your Web Method is actually returning the value?