Jquery Ajax POST to C# WebMethod Errors with "Invalid JSON primitive: System.Object."

Question

Morning all. I've been trying to do this for weeks now but keep going in circles. I have a simple jQuery Ajax function that POSTS Data to a c# function in the code behind.

Basically want to pass a list of selected checkbox fields to be processed. When I submit it, I can see the request being made and the json being sent:

{"item":["Section1","Section2","Section2Sub1","Section2Sub2","Section3"]}

It gets to the server side but when trying to deserialize it, it kicks me back the following error message:

"Invalid JSON primitive: System.Object."

var selection = serializer.Deserialize<string>(item.ToString());

Here's my code snippet:

 
client side
 $("#Submit").click(function (e) {
 var count = 0;
 var countChecked = 0;
 areaObj = [];
 $('input[type=checkbox]').each(function () {
 count++;
 if (this.checked) {
 //countChecked++;
 //tmp = {
 // "Area": $(this).attr("id")
 //};
 areaObj.push($(this).attr("id"));
 }
 });
 });
 function subClick(item) {
 $.ajax({
 type: "POST",
 url: "Default.aspx/SubData",
 data: JSON.stringify({ item: item }),
 //data: "{'item':" + JSON.stringify(item) + "}",
 dataType: "json",
 contentType: "application/json; charset=utf-8"
 });
 };
c# Default.aspx.cs
[WebMethod]
 public static string SubData(Selection item)
 {
 var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
 //ERROR OCCURS HERE
 var selection = serializer.Deserialize(item.ToString());
 return "this is successful";
 }
 public class Selection
 {
 public string Title { get; set; }
 public string Description { get; set; }
 public List KeyValues { get; set; }
 }
 public class KeyValues
 {
 public int AreaID { get; set; }
 public string Area { get; set; }
 public int Value { get; set; }
 }

Can anyone offer any pointers on what is going wrong?

• Rob: Your use of item.ToString() indicates to me that you're not actually parsing the json you think you are. You're parsing the text System.Object which is the result of .ToString() on an object. If you put a breakpoint on the deserialize line, you'll see that item is not a string.
• Rob: It further looks like item is already the deserialized object.
• Nick: slaps forehead Of course it is. I've spent so long looking at this I became a bit snow blind to it.... Thanks Rob! Can you "Answer the question" and i'll mark it as the solution
• Rob: No worries mate, happy it helped :)

Answer 1

public static string SubData(Selection item)
{
 var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
 //ERROR OCCURS HERE
 var selection = serializer.Deserialize(item.ToString());
 return "this is successful";
}

Here, item is not a string (and thus not the JSON being sent). Since you're calling ToString() on it, it's likely the library is trying to deserialize text similar to System.Object - which will fail.

At a quick glance at the code, it looks like item is already deserialized for you, so you don't need to do anything further