メッセージエラー：System.InvalidCastExceptionのは：指定されたキャストは有効ではありません10

Question

私の次のコードである私のMySQLデータベースへの簡単なHTTPリクエスト

using System; 
using Android.App; 
using Android.Content; 
using Android.Runtime; 
using Android.Views; 
using Android.Widget; 
using Android.OS; 
using System.Json; 
using System.Net; 
using System.Threading.Tasks; 
using System.IO; 
using Newtonsoft.Json; 
using Microsoft.CSharp; 

namespace API_Test 
{ 
[Activity(Label = "API_Test", MainLauncher = true, Icon = "@drawable/icon")] 
public class MainActivity : Activity 
{ 

    private Button button; 
    private EditText reponseAPI; 

    protected override void OnCreate(Bundle bundle) 
    { 
     base.OnCreate(bundle); 

     // Set our view from the "main" layout resource 
     SetContentView(Resource.Layout.Main); 

     // Get the latitude/longitude EditBox and button resources: 
     button = FindViewById<Button>(Resource.Id.btnCall); 

     // When the user clicks the button ... 
     button.Click += async (sender, e) => { 


      string url = "http://192.168.X.XX/API_xxxx.php?xxxxxx"; 


      JsonValue json = await FetchWeatherAsync(url); 
      //ParseAndDisplay (json); 
     };   
    } 


    private async Task<JsonValue> FetchWeatherAsync(string url) 
    { 
     // Create an HTTP web request using the URL: 
     HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(url)); 
     request.ContentType = "application/json"; 
     request.Method = "GET"; 

     // Send the request to the server and wait for the response: 
     using (WebResponse response = await request.GetResponseAsync()) 
     { 
      // Get a stream representation of the HTTP web response: 
      using (Stream stream = response.GetResponseStream()) 
      { 
       // Use this stream to build a JSON document object: 
       JsonValue jsonDoc = await Task.Run(() => JsonObject.Load(stream)); 
       Console.Out.WriteLine("Test: {0}", jsonDoc.ToString()); 

       // Return the JSON document: 
       return jsonDoc; 
      } 
     } 
    } 


    private void ParseAndDisplay(JsonValue json) 
    { 
     reponseAPI = FindViewById<EditText>(Resource.Id.reponseAPI); 

     //dynamic Toto = JsonObject.Parse(json); 
     //string lolo = Toto.id; 
     //reponseAPI.Text = lolo; 
     //var m = JsonConvert.DeserializeObject<dynamic>(json); 
     //Console.Out.WriteLine("oooo"); 

     //string name = m.id;  


    } 
} 
} 

私はそれをデバッグしようとすると、以下のオープンポップアップメッセージ

"未処理の例外：System.InvalidCastException：指定されたキャストが無効です。"

解決策を探しています。再帰的な答えはType値についてですが、現時点では、データを取り戻すためにC＃でデータを解析しようとしません。

私はVMとXamarinの初心者ですので、「完全な例外」は次のコードです。まず

08-22 12:03:39.569 D/Mono (5472): Image addref System.Json[0x9d292980] -> System.Json.dll[0x9c62fa00]: 1 
08-22 12:03:39.569 D/Mono (5472): Assembly System.Json[0x9d292980] added to domain RootDomain, ref_count=1 
08-22 12:03:39.569 D/Mono (5472): AOT module 'System.Json.dll.so' not found: dlopen failed: library "/data/app/API_Test.API_Test-1/lib/x86/libaot-System.Json.dll.so" not found 
08-22 12:03:39.570 D/Mono (5472): AOT module '/Users/builder/data/lanes/3540/1cf254db/source/monodroid/builds/install/mono-x86/lib/mono/aot-cache/x86/System.Json.dll.so' not found: dlopen failed: library "/data/app/API_Test.API_Test-1/lib/x86/libaot-System.Json.dll.so" not found 
08-22 12:03:39.570 D/Mono (5472): Config attempting to parse: 'System.Json.dll.config'. 
08-22 12:03:39.570 D/Mono (5472): Config attempting to parse: '/Users/builder/data/lanes/3540/1cf254db/source/monodroid/builds/install/mono-x86/etc/mono/assemblies/System.Json/System.Json.config'. 
08-22 12:03:39.570 D/Mono (5472): Assembly Ref addref API_Test[0xad97b760] -> System.Json[0x9d292980]: 2 
08-22 12:03:39.570 D/Mono (5472): Assembly Ref addref System.Json[0x9d292980] -> mscorlib[0xad97b700]: 14 
Loaded assembly: System.Json.dll 
08-22 12:03:39.589 D/Mono (5472): Assembly Ref addref API_Test[0xad97b760] -> System[0xb077ce20]: 3 
08-22 12:03:39.646 D/Mono (5472): Assembly Ref addref Mono.Android[0xb077cee0] -> System[0xb077ce20]: 4 
08-22 12:03:39.675 D/Mono (5472): DllImport searching in: '__Internal' ('(null)'). 
08-22 12:03:39.675 D/Mono (5472): Searching for 'java_interop_jnienv_call_int_method'. 
08-22 12:03:39.675 D/Mono (5472): Probing 'java_interop_jnienv_call_int_method'. 
08-22 12:03:39.675 D/Mono (5472): Found as 'java_interop_jnienv_call_int_method'. 
08-22 12:03:39.683 D/Mono (5472): DllImport searching in: '__Internal' ('(null)'). 
08-22 12:03:39.683 D/Mono (5472): Searching for 'java_interop_jnienv_get_static_field_id'. 
08-22 12:03:39.683 D/Mono (5472): Probing 'java_interop_jnienv_get_static_field_id'. 
08-22 12:03:39.683 D/Mono (5472): Found as 'java_interop_jnienv_get_static_field_id'. 
08-22 12:03:39.684 D/Mono (5472): DllImport searching in: '__Internal' ('(null)'). 
08-22 12:03:39.684 D/Mono (5472): Searching for 'java_interop_jnienv_get_static_object_field'. 
08-22 12:03:39.684 D/Mono (5472): Probing 'java_interop_jnienv_get_static_object_field'. 
08-22 12:03:39.684 D/Mono (5472): Found as 'java_interop_jnienv_get_static_object_field'. 
08-22 12:03:39.687 D/Mono (5472): DllImport searching in: '__Internal' ('(null)'). 
08-22 12:03:39.687 D/Mono (5472): Searching for 'java_interop_jnienv_call_nonvirtual_boolean_method_a'. 
08-22 12:03:39.687 D/Mono (5472): Probing 'java_interop_jnienv_call_nonvirtual_boolean_method_a'. 
08-22 12:03:39.687 D/Mono (5472): Found as 'java_interop_jnienv_call_nonvirtual_boolean_method_a'. 
Thread started: #2 
Thread started: <Thread Pool> #3 
Thread started: <Thread Pool> #4 
08-22 12:03:39.772 D/Mono (5472): [0x9bb7f930] worker starting 
Thread started: <Thread Pool> #5 
08-22 12:03:39.810 D/Mono (5472): [0x9b97f930] worker starting 
Thread started: <Thread Pool> #6 
08-22 12:03:39.878 D/Mono (5472): [0x9bb7f930] hill climbing, change max number of threads 2 
08-22 12:03:39.948 D/Mono (5472): Assembly Ref addref System.Json[0x9d292980] -> System.Core[0x9d2913c0]: 4 
08-22 12:03:39.962 D/Mono (5472): Assembly Ref addref System.Json[0x9d292980] -> System[0xb077ce20]: 5 
08-22 12:03:40.011 D/Mono (5472): DllImport attempting to load: '/system/lib/liblog.so'. 
08-22 12:03:40.011 D/Mono (5472): DllImport loaded library '/system/lib/liblog.so'. 
08-22 12:03:40.011 D/Mono (5472): DllImport searching in: '/system/lib/liblog.so' ('/system/lib/liblog.so'). 
08-22 12:03:40.011 D/Mono (5472): Searching for '__android_log_print'. 
08-22 12:03:40.011 D/Mono (5472): Probing '__android_log_print'. 
08-22 12:03:40.011 D/Mono (5472): Found as '__android_log_print'. 
08-22 12:03:40.011 I/mono-stdout(5472): ducon: [{"id": "1", "nom": "Dylan", "prenom": "Bob"}] 
ducon: [{"id": "1", "nom": "Dylan", "prenom": "Bob"}] 
08-22 12:03:40.016 D/Mono (5472): Assembly Ref addref API_Test[0xad97b760] -> Newtonsoft.Json[0xad97bd00]: 2 
08-22 12:03:40.016 D/Mono (5472): Assembly Ref addref Newtonsoft.Json[0xad97bd00] -> System.Runtime[0xad97bee0]: 3 
Unhandled Exception: 

System.InvalidCastException: Specified cast is not valid. 

Answer 1

は、あなたがパッケージを追加する必要があります：

public class MyUser 
{ 
    public int id {get;set;} 
    public string name {get;set;} 
} 

、その後、例えば、Newtonsoft.Json

private async Task<JsonValue> FetchWeatherAsync(string url) 
{ 
    //return json string 
} 

はJSONオブジェクトを結合するための準備、モデルを作成し、解析オブジェクトへのjson文字列

private void ParseAndDisplay(string JsonString) 
{ 
var data = JsonConvert.DeserializeObject<MyUser>(jsonString); 
var UserID = data.id; //get property value 
//.....set something TextView value 
} 

試してみてください！