Xamarin - 无法从源类型转换为目标类型 [英] Xamarin - Cannot cast from source type to destination type

问题描述

我想在一个动态变量反序列化一个JSON文件，但它抛出

I want to deserialize a json document in a dynamic variable, however it throws

错误：

[MonoDroid] UNHANDLED EXCEPTION:
[MonoDroid] System.InvalidCastException: Cannot cast from source type to destination type.
[MonoDroid] at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () <IL 0x00011, 0x00078>
[MonoDroid] at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<ThrowAsync>m__0 (object) <IL 0x00006, 0x0006b>
[MonoDroid] at Android.App.SyncContext/<Post>c__AnonStorey0.<>m__0 () [0x00000] in /Users/builder/data/lanes/1879/5f55a9ef/source/monodroid/src/Mono.Android/src/Android.App/SyncContext.cs:18
[MonoDroid] at Java.Lang.Thread/RunnableImplementor.Run () [0x0000b] in /Users/builder/data/lanes/1879/5f55a9ef/source/monodroid/src/Mono.Android/src/Java.Lang/Thread.cs:36
[MonoDroid] at Java.Lang.IRunnableInvoker.n_Run (intptr,intptr) [0x00009] in /Users/builder/data/lanes/1879/5f55a9ef/source/monodroid/src/Mono.Android/platforms/android-19/src/generated/Java.Lang.IRunnable.cs:71
[MonoDroid] at (wrapper dynamic-method) object.461b928a-1fde-4250-8fe8-4ab69b1f0acd (intptr,intptr) <IL 0x00011, 0x0003b>
[art] JNI RegisterNativeMethods: attempt to register 0 native methods for md52ce486a14f4bcd95899665e9d932190b.JavaProxyThrowable
[AndroidRuntime] Shutting down VM   

code：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Json;
using System.Net;
using System.IO;
using System.Threading.Tasks;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;

using Newtonsoft.Json;

namespace HomecheckApp {
    [Activity(Label = "LoginActivity", MainLauncher = true)]
    public class LoginActivity : Activity {
        private const string apiKey = "*********************************************";
        protected override void OnCreate(Bundle bundle) {
            base.OnCreate(bundle);
            SetContentView(Resource.Layout.Login);

            EditText email = FindViewById<EditText>(Resource.Id.editEmail);
            EditText password = FindViewById<EditText>(Resource.Id.editPassword);
            Button loginButton = FindViewById<Button>(Resource.Id.loginButton);
//          string url = "http://homecheck.192.168.1.102.xip.io/appapi/finduser?email" + email.Text + "&pass=" + password.Text + "&key=" + apiKey;
            loginButton.Click += async (sender, e) => {
                string url = "http://homecheck.********.eu/appapi/finduser?email=" + email.Text + "&pass=" + password.Text + "&key=" + apiKey;
                JsonValue json = await FetchUserAsync(url, apiKey);
     //This is where it breaks
                dynamic userInfo = JsonConvert.DeserializeObject(json);
    //*********
                Console.WriteLine("Email is: " + userInfo.email);
            };  
        }

        private async Task<JsonValue> FetchUserAsync(string url, string apiKey) {
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
            request.ContentType = "application/json";
            request.Method = "POST";
            using(WebResponse response = await request.GetResponseAsync()) {
                using(Stream stream = response.GetResponseStream()) {
                    JsonValue jsonResponse = await Task.Run(() => JsonObject.Load(stream));
                    Console.WriteLine(jsonResponse.ToString());
                    return jsonResponse;
                }
            }
        }
    }

}

的Json如下：

<$c$c>{\"error\":false,\"id\":3,\"name\":\"***********\",\"surname\":\"*******\",\"email\":\"***********@gmail.com\",\"gsm\":\"1239102312930\",\"company\":\"\",\"address\":3}

当我尝试使用 JObject.Parse 来反序列化出现同样的错误。这是与IDE本身的问题（我使用Xamarin工作室），或者是其他什么东西？

Same error appears when I try to deserialize it using JObject.Parse. Is this a problem with the IDE itself (I'm using Xamarin Studio) or is it something else ?

推荐答案

JsonConvert.DeserializeObject（）需要字符串作为第一个参数。但是，您提供键入 JsonValue 的对象。我不明白为什么编译器甚至允许这一点，但是这是最有可能你的问题的根源。

JsonConvert.DeserializeObject() takes a string as its first parameter. However, you are supplying an object of type JsonValue. I'm not quite sure why the compiler is even allowing this, but that's most likely the source of your problem.

只要改变

dynamic userInfo = JsonConvert.DeserializeObject(json);

到

dynamic userInfo = JsonConvert.DeserializeObject(json.ToString());

至少应该解决您的例外。这可能不是最完美的解决方案，但是。

Should at least fix your exception. This might not be the most elegant solution, however.

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