我的以下代码是对我的MYSql数据库的简单HTTP请求
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;
}
}
}
当我尝试调试它时，弹出一个弹出窗口，显示以下消息
“未处理的异常：System.InvalidCastException：指定的强制转换无效。”
我正在寻找stackoverflow中的解决方案。循环答案是关于Type值的，但目前我不会尝试在C＃中解析我的数据，只是为了获取我的数据。
我是VM和Xamarin的初学者所以我希望“完全例外”是以下代码。
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.
答案 0 :(得分：0)
首先，你必须添加包：Newtonsoft.Json
private async Task<JsonValue> FetchWeatherAsync(string url)
{
//return json string
}
创建模型，准备绑定json对象，例如
public class MyUser
{
public int id {get;set;}
public string name {get;set;}
}
然后，将json字符串解析为object
private void ParseAndDisplay(string JsonString)
{
var data = JsonConvert.DeserializeObject<MyUser>(jsonString);
var UserID = data.id; //get property value
//.....set something TextView value
}