Error sending JSON object to asp.net WebMethod, using jQuery

Question

I get an error of "Cannot convert object of type System.String' to type 'System.Collections.Generic.List'1[...+ContactHolder]'"

This is my C# code:

public class ContactHolder{
    public String Name { get; set; }
    public String Address { get; set; }
}

[WebMethod]
public static string AddContact(Object items){
    List<ContactHolder> contacts = new JavaScriptSerializer().ConvertToType<List<ContactHolder>>(items);
    return String.Format("You added {0} contacts!", contacts.ToString());
}

This is my Javascript code (note I have included jquery-1.4.1.js and json2.js in my project)

function Test() {
var arr = new Array();
var contact = new Object();
contact.Name = "Ben";
contact.Address = "Ohio";

var contact2 = new Object();
contact.Name = "Jon";
contact.Address = "Illinois";

arr[1] = contact;
arr[2] = contact2;

var DTO = JSON.stringify(arr);
PageMethods.AddContact(DTO, OnMyMethodComplete);}

function OnMyMethodComplete(result, userContext, methodName) {alert(result);}

When I pass DTO into myPageMethod it looks like this: "[{"Name":"Ben","Address":"Ohio"},{"Name":"Jon","Address":"Illinois"}]"

When it appears in my WebMethod as items it looks like this: "[{\"Name\":\"Ben\",\"Address\":\"Ohio\"},{\"Name\":\"Jon\",\"Address\":\"Illinois\"}]"

The code errors on the call to JavaScriptSerializer().ConvertToType, the message is {"Cannot convert object of type System.String' to type 'System.Collections.Generic.List'1[...+ContactHolder]'"}

What do I need to do to make this work?

Can you post the implementation of PageMethods.AddContact? I think it would be more easier to help you if we know exactly what is going on behind the scenes. — Herberth Amaral
– Herberth Amaral, Commented Feb 15, 2011 at 19:58
Why do you not declare the WebMethod parameter as ContactHolder[] ? Seems as if ASP.Net sees a scalar parameter (Object), and converts the JSON string into a .Net string. — devio
– devio, Commented Feb 15, 2011 at 19:58
@Herberth - I do include the code for AddContact. It is in the C# code section. — Ben Hoffman
– Ben Hoffman, Commented Feb 15, 2011 at 20:08
@Devio - I tried that, I get the same error. It just changes to can't convert into List. — Ben Hoffman
– Ben Hoffman, Commented Feb 15, 2011 at 20:09

Community · Accepted Answer · 2017-05-23 11:55:44Z

4

Passing parameter to WebMethod with jQuery Ajax

Remove JSON.stringify or do like this:

sending JSON object successfully to asp.net WebMethod, using jQuery

edited May 23, 2017 at 11:55

CommunityBot

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answered Feb 15, 2011 at 20:28

Artem Koshelev

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2 Comments

Dave Ward Over a year ago

This is correct. When using the ASP.NET AJAX service proxy helper methods, the parameters are automatically JSON serialized before sending. You do need the JSON.stringify() call if you're calling the service directly, without the service proxy. For example, if you're using jQuery's $.ajax().

Artem Koshelev Over a year ago

Thanks Dave, I just found your answer in similar topic and linked it.

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