Error calling webmethod

Question

I’m creating a webmetod that will make the autocomplete of some fields on my screen, however I’m getting error 500

        <System.Web.Services.WebMethod>
    <System.Web.Script.Services.ScriptMethod(ResponseFormat:=ResponseFormat.Json, UseHttpGet:=False)>
            Public Function AutoComplete(ByVal prefixText As String) As String
                Dim resposta As string =  "funciona"


                Return Newtonsoft.Json.JsonConvert.SerializeObject(resposta)
            End Function

as you can see it is quite simple just to see if it returns the server message

My javascript

function buscaPorParametro(campo) {
            var valorDigitado = $("input[name='" + campo +"']")
            console.log(txtBox.val())
            $.ajax({
                data: JSON.stringify("{  prefixText: '" + valorDigitado.val() + "' }"),
                dataType: "json",
                url: url,
                type: "POST",
                contentType: "application/json; charset=utf-8",
                success: OnSuccess,
                error: onError
            });
        }
        function OnSuccess(data) {


        }
        function onError(err) {
            console.log(err);
            $('#LoadingPanel').css('display', 'none');
        }

error returned from server

"{"Message":"Cannot convert object of type \u0027System.String\u0027 to type \u0027System.Collections.Generic.IDictionary`2[System.String,System.Object]\u0027","StackTrace":"   at System.Web.Script.Serialization.ObjectConverter.ConvertObjectToTypeInternal(Object o, Type type, JavaScriptSerializer serializer, Boolean throwOnError, Object\u0026 convertedObject)\r\n   at System.Web.Script.Serialization.ObjectConverter.ConvertObjectToTypeMain(Object o, Type type, JavaScriptSerializer serializer, Boolean throwOnError, Object\u0026 convertedObject)\r\n   at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit)\r\n   at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize[T](String input)\r\n   at System.Web.Script.Services.RestHandler.GetRawParamsFromPostRequest(HttpContext context, JavaScriptSerializer serializer)\r\n   at System.Web.Script.Services.RestHandler.GetRawParams(WebServiceMethodData methodData, HttpContext context)\r\n   at System.Web.Script.Services.RestHandler.ExecuteWebServiceCall(HttpContext context, WebServiceMethodData methodData)","ExceptionType":"System.InvalidOperationException"}"

someone would tell me where I’m going wrong?

Thank you

Answer 1

As in your signature Webservice you expect only one string, is exactly what you should go through when consuming it via javascript.

When sending data via javascript thus:

JSON.stringify("{  prefixText: '" + valorDigitado.val() + "' }")

The value will be converted into something like this:

var dictionary = new Dictionary<string, object>();
dictionary.Add("prefixText","xpto");

And when trying to consume your Webservice, there will be conversion error as a IDictionary cannot be converted to string.

I suggest you change your Webservice subscription to that:

Public Function AutoComplete(ByVal dados As Dictionary<string, Object>) As String

Or just send one string via javascript.

Answer 2

In the end I managed to solve the problem by typing the method signature

 Public Function AutoCompleteCodigo(ByVal _getDados As Dados) As String

End Function

and in javascript

function buscaPorParametro(campo) {            
        var dados = {};
        dados._getDados = {};
        dados._getDados.Descricao = $(this).attr("Descricao");
        $.ajax({ data: JSON.stringify(dados),
            dataType: "json",
            url: url,
            type: "POST",
            contentType: "application/json; charset=utf-8",
            success: OnSuccess,
            error: onError
        });
    }
    function OnSuccess(data) {

        alert('good');
    }
    function onError(err) {
        console.log(err);
        $('#LoadingPanel').css('display', 'none');
    }

where the variables below are the construction of the object being sent to the webmethod

var dados = {};

data. _getDados = {};