java.lang.InstantiationException：類沒有零參數構造函數錯誤

Question

我讀過其他線程存在，但沒有人能夠解決我的問題。

我正在構建一個應用程序，它在沒有互聯網並將它們存儲到數據庫時緩存消息。這個想法是當有網絡連接時，它從數據庫中提取數據並在後臺發送消息 - 爲此我製作了一個廣播接收器，並讓它接收到「android.net.conn.CONNECTIVITY_CHANGE」廣播 - 這使得應用程序POST消息服務器

我得到當網絡發生變化的錯誤：

java.lang.RuntimeException: Unable to instantiate receiver com.tanvirsingh.fragmentsdemo.NetworkChangeReceiver: java.lang.InstantiationException: java.lang.Class<com.tanvirsingh.fragmentsdemo.NetworkChangeReceiver> has no zero argument constructor 

廣播接收器類（NetworkChangeReceiver.java）：

public class NetworkChangeReceiver extends BroadcastReceiver{ 

    private static final String TAGNCR = "JSON"; 

    private final Handler handler; // Handler used to execute code on the UI thread 

    public NetworkChangeReceiver(Handler handler) { 
     this.handler = handler; 
    } 

    DataBaseHelper myDB; 
    final String MESSAGES_ENDPOINT = ""; 



    @Override 
    public void onReceive(Context context, Intent intent) { 

     int[] type = {ConnectivityManager.TYPE_MOBILE, ConnectivityManager.TYPE_WIFI}; 
     if (isNetworkAvailable(context) == true){ 
      //check for messages to be sent 
      myDB = new DataBaseHelper(context); 

      Cursor res = myDB.getAllData(); 
      if (res.getCount() == 0) 
      { 
       Log.d(TAG,"No data found"); 
       return; 

      } 

      StringBuffer buffer = new StringBuffer(); 
      while(res.moveToNext()){ 
       buffer.append("Params: " + res.getString(0)+ "\n"); 
      } 

      Log.d(TAGNCR,buffer.toString()); 

      return; 

     } else { 

     } 
    } 

    public void SendMessageFromDB(RequestParams param){ 

     AsyncHttpClient client = new AsyncHttpClient(); 

     //pusher 
     PusherOptions options = new PusherOptions(); 
     options.setCluster(""); 
     Pusher pusher = new Pusher("", options); 

     Channel channel = pusher.subscribe("my-channel"); 

     channel.bind("my-event", new SubscriptionEventListener() { 
      @Override 
      public void onEvent(String channelName, String eventName, final String data) { 
       System.out.println(data); 
      } 
     }); 

     pusher.connect(); 

     final RequestParams params = param; 

     client.post(MESSAGES_ENDPOINT + "/messages", params, new JsonHttpResponseHandler() { 

       @Override 
       public void onSuccess(int statusCode, Header[] headers, JSONObject response) { 
        handler.post(new Runnable() { 
         @Override 
         public void run() { 
          Log.d(TAG, params.toString()); 
         } 
        }); 
       } 

       @Override 
       public void onFailure(int statusCode, Header[] headers, String responseString, Throwable throwable) { 
        //Toast.makeText(, "Something went wrong :(", Toast.LENGTH_LONG).show(); 
       } 
      }); 

      return; 

    } 



    //function to check if internet is available 
    private static boolean isNetworkAvailable(Context context){ 
     try{ 
      ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE); 
      NetworkInfo activeNetwork = cm.getActiveNetworkInfo(); 
      if (activeNetwork != null) { // connected to the internet and not in Airplane mode 
       if (activeNetwork.getType() == ConnectivityManager.TYPE_WIFI) { 
        // connected to wifi 
        Toast.makeText(context, activeNetwork.getTypeName() + " Connected", Toast.LENGTH_SHORT).show(); 
        return true; 
       } else if (activeNetwork.getType() == ConnectivityManager.TYPE_MOBILE) { 
        // connected to the mobile data 
        Toast.makeText(context, activeNetwork.getTypeName() + " Connected", Toast.LENGTH_SHORT).show(); 
        return true; 
       } 
      } else { 
       // not connected to the internet 
       Toast.makeText(context, "No internet connection available!", Toast.LENGTH_SHORT).show(); 

      } 
     } catch (Exception e){ 
      return false; 
     } 
     return false; 
    } 
} 

堆棧跟蹤的要求：

04-05 16:36:29.828 3420-3420/com.tanvirsingh.fragmentsdemo E/AndroidRuntime: FATAL EXCEPTION: main 
                      Process: com.tanvirsingh.fragmentsdemo, PID: 3420 
                      Theme: themes:{default=overlay:system, iconPack:com.baranovgroup.nstyle, fontPkg:com.baranovgroup.nstyle, com.android.systemui=overlay:com.baranovgroup.nstyle, com.android.systemui.navbar=overlay:system} 
                      java.lang.RuntimeException: Unable to instantiate receiver com.tanvirsingh.fragmentsdemo.NetworkChangeReceiver: java.lang.InstantiationException: java.lang.Class<com.tanvirsingh.fragmentsdemo.NetworkChangeReceiver> has no zero argument constructor 
                       at android.app.ActivityThread.handleReceiver(ActivityThread.java:2752) 
                       at android.app.ActivityThread.-wrap14(ActivityThread.java) 
                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1440) 
                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                       at android.os.Looper.loop(Looper.java:148) 
                       at android.app.ActivityThread.main(ActivityThread.java:5471) 
                       at java.lang.reflect.Method.invoke(Native Method) 
                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
                       at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:102) 
                       Caused by: java.lang.InstantiationException: java.lang.Class<com.tanvirsingh.fragmentsdemo.NetworkChangeReceiver> has no zero argument constructor 
                       at java.lang.Class.newInstance(Native Method) 
                       at android.app.ActivityThread.handleReceiver(ActivityThread.java:2747) 
                       at android.app.ActivityThread.-wrap14(ActivityThread.java)  
                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1440)  
                       at android.os.Handler.dispatchMessage(Handler.java:102)  
                       at android.os.Looper.loop(Looper.java:148)  
                       at android.app.ActivityThread.main(ActivityThread.java:5471)  
                       at java.lang.reflect.Method.invoke(Native Method)  
                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)  
                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)  
                       at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:102)  

Answer 1

Broadcast Receiver與Fragment相同和許多其他類應該有默認構造函數沒有參數相同。

只需添加默認的構造函數：

public NetworkChangeReceiver() { 
} 

之所以如此，是因爲Android系統知道類和它的名包，但什麼都不知道它的參數。 它採用反射，像

Class c = Class.forName(className); 
    YourBroadcastReceiver broadcastReceiver = (YourBroadcastReceiver)c.newInstance(); 

沒有默認constgructor的newInstance（）會產生錯誤。

UPD：

在你的情況，你應該從廣播接收器去除SendMessageFromDB方法單獨的類。