ASP.NET WebMethod receive JSON string?

Question

I'm trying to call a WebMethod via ajax with a JSON string as follows:

                let jsonData = JSON.stringify({test: "Test"});

                $.ajax({
                    type: "POST",
                    url: "WebForm.aspx/DoStuff",
                    data: '{data: "' + jsonData + '" }',
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: OnSuccess,
                    failure: function (response) {
                        alert(response.d);
                    }
                });

However, I get a HTTP 500 internal error.

I would like to parse the JSON string in the WebMethod as I do not know the values at runtime. The WebMethod looks like this:

        [WebMethod]
        public static string DoStuff(string data)
        {
            var keyValuePairs = JsonConvert.DeserializeObject<Dictionary<string, string>>(data);
            foreach (var key in keyValuePairs.Keys)
            {
                ...
            }

            return ...
        }

Adam · Accepted Answer · 2020-04-30 16:32:26Z

Ok, the problem was with the formatting of the data in the ajax request. The following worked:

            let jsonData = JSON.stringify({test: "Test"});
            let data = { data: jsonData };

            $.ajax({
                type: "POST",
                url: "SomePage.aspx/DoStuff",
                data: JSON.stringify(data),
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: OnSuccess,
                failure: function (response) {
                    alert(response.d);
                }
            });

Sam · Accepted Answer · 2020-04-30 11:30:56Z

Try parsing the json data to a JObject if you're using newtonsoft, or a JSONDocument if you want to use Microsofts Json library in .net core 3 System.Text.Json

https://www.newtonsoft.com/json/help/html/ParseJsonObject.htm

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-how-to#use-jsondocument-for-access-to-data

Example using System.Text.Json

using (JsonDocument jsonDoc = JsonDocument.Parse(data))
{
    JsonElement root = jsonDoc.RootElement;
    JsonElement dataEl = root.GetProperty("Data");
    var testEl = dataEl.GetProperty("Test")
    ...
}

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