Ajax请求asp.net mvc控制器返回500 - 内部服务器错误

I have these two selects on a view:

我在视图上有这两个选择：

<select class="input-sm form-control input-s-sm inline" onchange="carregarCidades()" id="comboEstado">
    ...
</select>

<select class="input-sm form-control input-s-sm inline" id="comboCidade">
   ...
</select>

The first represents a State, and when I select it I want to execute the carregarCidades function to load the cities of that stat and them load them in the other select. Here is the function:

第一个代表一个State，当我选择它时，我想执行carregarCidades函数来加载该stat的城市，然后将它们加载到另一个select中。这是功能：

function carregarCidades() {
    var url = "@Url.Action("CarregarCidades", "Usuario")";

    var estado = $("#comboEstado").find(":selected").text();

    $.get(url, { pEstado: estado }, function (cidades) {
        $("#comboCidade").html(""); // clear before appending new list 
        $.each(cidade, function (i, cidade) {
            $("#comboCidade").append(
                $('<option></option>').val(cidade.id_cidade).html(cidade.cidade));
        });
    });
}

Now, here is the CarregarCidades action in the UsuarioController:

现在，这是UsuarioController中的CarregarCidades操作：

public ActionResult CarregarCidades(string pEstado)
{
    string cCidades = oVFP.BuscaCidade(pEstado);

    DataSet dsC = new DataSet();
    dsC.ReadXml(new StringReader(cCidades));

    JsonResult result = Json(dsC.Tables["curretorno"]);
    return result;
}

I'm debugging the action and apparently everything is ok:

我正在调试动作，显然一切正常：

But, after the Action returns the Json result, the callback funcion is not called on the jquery code and I got a 500 internal server error in my console.

但是，在Action返回Json结果之后，jquery代码上没有调用回调函数，我的控制台中出现了500内部服务器错误。

2 个解决方案

#1

You have to JsonAllowRequestbehavior parameter to AllowGet, by default it is DenyGet :

您必须将JsonAllowRequestbehavior参数添加到AllowGet，默认情况下它是DenyGet：

JsonResult result = Json(dsC.Tables["curretorno"],JsonRequestBehavior.AllowGet);

You can read about Why it is needed on this post.

您可以在这篇文章中阅读有关为什么需要它的信息。

#2

I would first make sure your method has the [WebMethod] attribute above its declaration.

我首先要确保您的方法在其声明之上具有[WebMethod]属性。

The second thing I would suggest is returning your Json like this:

我建议的第二件事就是像这样返回你的Json：

return Json(result, JsonRequestBehavior.AllowGet);

Generally it is one of or both of these issues that gives you a 500 error.

通常，这些问题中的一个或两个都会导致500错误。

Edit:

编辑：

Declaring it as a [WebMethod] may not be necessary.

将其声明为[WebMethod]可能没有必要。

#1