Invalidcastexception JsonConvert.DeserializeObject

Question

我得到一个无效的强制转换异常，指定的强制转换是无效的。在这一行:

RootObject mountain = JsonConvert.DeserializeObject<RootObject>(json1);

从文档来看，这应该没问题?我可以看到控制台输出是否正常?

反应:[{"Height_ft":2999.0,"Height_m":914.0,"ID":"c1","Latitude":57.588007，"Longitude":-5.5233564，"Name":"Beinn Dearg"，"snowCover"湿度":0.81:4.99,63.0"温度":}]

        Spinner spinner = (Spinner)sender;
        string urlmountain = "http://removed.azurewebsites.net/api/Mountains?name=";
        JsonValue json1 = FetchMountain(urlmountain+string.Format("{0}", spinner.GetItemAtPosition(e.Position)));
        //below.................................
        RootObject mountain = JsonConvert.DeserializeObject<RootObject>(json1); //this line
        string toast = mountain.Name;
        Toast.MakeText(this, toast, ToastLength.Long).Show();
    private JsonValue FetchMountain(string urlmountain)
    {
        // Create an HTTP web request using the URL:
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(urlmountain));
        request.ContentType = "application/json";
        request.Method = "GET";
        // Send the request to the server and wait for the response:
        using (WebResponse response = request.GetResponse())
        {
            // Get a stream representation of the HTTP web response:
            using (Stream stream = response.GetResponseStream())
            {
                // Use this stream to build a JSON document object:
                JsonValue jsonDoc1 = JsonObject.Load(stream);
                Console.Out.WriteLine("Response: {0}", jsonDoc1.ToString());
                // Return the JSON document:
                return jsonDoc1;
            }
        }
    }
    public class RootObject
    {
        public string ID { get; set; }
        public double? Latitude { get; set; }
        public double? Longitude { get; set; }
        public string Name { get; set; }
        public double? Height_m { get; set; }
        public double? Height_ft { get; set; }
        public double? temperature { get; set; }
        public double? humidity { get; set; }
        public double? snowCover { get; set; }
        public override string ToString()
        {
            return Name;
        }
    }

Answer 1

返回的json数据是一个对象数组，而不是单个对象，由左括号和右括号[]表示。您需要反序列化为数组或列表:

var mountains = JsonConvert.DeserializeObject<List<RootObject>>(json);

要访问反序列化负载中的第一个mountain，请使用.FirstOrDefault()。

var mountain = mountains.FirstOrDefault();
if (mountain != null)
{
    string toast = mountain.Name;
    Toast.MakeText(this, toast, ToastLength.Long).Show();
}

Answer 2

看起来JSON是一个对象数组。您应该能够反序列化数组并获得第一个，如下所示:

RootObject mountain = JsonConvert.DeserializeObject<RootObject[]>(json1)[0];

需要注意的一点是，你在这里混合了一些技术。JsonValue来自System.Json命名空间，而JsonConvert来自Newtonsoft.Json(即JSON.Net)命名空间。如果你想严格使用JSON。Net，您可以这样做:

private RootObject FetchMountain(string urlmountain)
{
    // Create an HTTP web request using the URL:
    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(urlmountain));
    request.ContentType = "application/json";
    request.Method = "GET";
    using (WebResponse response = request.GetResponse())
    using (Stream stream = response.GetResponseStream())
    using (StreamReader streamReader = new StreamReader(stream))
    {
        JsonSerializer serializer = new JsonSerializer();
        RootObject[] mountains = (RootObject[])serializer.Deserialize(streamReader, typeof(RootObject[]));
        return (mountains.Length > 0) ? mountains[0] : null;
    }
}