Passing parameters in a jQuery ajax call to an ASP.NET webmethod

Question

I know there are more threads about this but they dont help me and I'm going insane here!

I wanna pass some parameters in to a web method using jQuery Ajax.

var paramList = '';
for(i = 0; i < IDList.length; i++){
    if (paramList.length > 0) paramList += ',';  
        paramList += '"' + 'id' + '":"' + IDList[i].value + '"';  
    }
    paramList = '{' + paramList + '}';  
    var jsonParams = JSON.stringify(paramList);


    $.ajax({
        type: "POST",          
        url: "editactivity.aspx/UpdateSequenceNumber",          
        data: jsonParams,
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function(response) {

        }
    });

In the ajax call, if I put data to paramList I get the error: "Invalid web service call, missing value for parameter: \u0027a\u0027."

If I put data to jsonParams I get the error:

"Cannot convert object of type \u0027System.String\u0027 to type \u0027System.Collections.Generic.IDictionary`2[System.String,System.Object]\u0027"

If I write out paramList, it's in a correct JSON format like {"id":"140", "id":"138"}

If I write out jsonParams, it's in an incorrect format like "{\"id\":\"140\",\"id\":\"138\"}"

The web method: (it doesn't do that much yet..)

[System.Web.Services.WebMethod]
    public static string UpdateSequenceNumber(string a, string b)
    {
         return a+b;
    }

What am I doing wrong? Can't seem to get this JSON thing right.

UPDATE:

After some help from the first answer I now send {"id":["138","140"]} in the AJAX request.

The web method now takes a string called id as the parameter instead.

[System.Web.Services.WebMethod]
public static string UpdateSequenceNumber(string id)
{
     return id;
}

Now I get the new error:

"Type \u0027System.Array\u0027 is not supported for deserialization of an array."

Ahmet Kakıcı · Accepted Answer · 2010-11-22 10:09:46Z

15

Your json parameter names must be same with the c# paramter names.

{"a":"140", "b":"138"}

If you are sending unknown number of parameters to server, you may concat at client-side into one parameter and then split at server-side.

answered Nov 22, 2010 at 10:09

Ahmet Kakıcı

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5 Comments

larschanders Over a year ago

Thanks, didnt know that. Now after I do var c = JSON.stringify({"id":list}); I get: {"id":["138","140"]} which looks alright. But know i get a new error when doing the ajax request: "Type \u0027System.Array\u0027 is not supported for deserialization of an array."

Ahmet Kakıcı Over a year ago

I didn't know that we can use List type as c# datatype with webmethod, thanks ;)

larschanders Over a year ago

Glad we could help each other :)

Ahmet Kakıcı Over a year ago

@larschanders i'm still getting upvotes but why don't u accept this as an answer? :)

Luis.Andrade Over a year ago

Guys I have this same issue but It didn't resolve it. Does anyone know if the jQuery could cause this problem?

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