運行時異常 - 無法啓動接收器

Question

當我使用Toast消息時，它正在工作。現在當我用alert對話框替換它時，我得到了運行時異常。這裏是我的代碼：

public class ConnectionReciever extends BroadcastReceiver { 

    @Override 
    public void onReceive(Context context, Intent intent) { 
     ConnectivityManager connectivityManager = (ConnectivityManager) context 
       .getSystemService(Context.CONNECTIVITY_SERVICE); 
     NetworkInfo activeNetwork = connectivityManager.getActiveNetworkInfo(); 
     if (activeNetwork != null && activeNetwork.isConnected()) { 
//   Toast.makeText(context, "Internet Connection is Active", 
//     Toast.LENGTH_LONG).show(); 
      AlertDialog successAlert=new AlertDialog.Builder(context).create(); 
      successAlert.setMessage("Internet Connection is Active"); 
      successAlert.show(); 

     } else { 
       AlertDialog failureAlert=new AlertDialog.Builder(context).create(); 
       failureAlert.setMessage("Internet Connection Timed Out....Please try again"); 
       failureAlert.show(); 
     } 

    } 
} 

它正確顯示吐司消息。現在，當我添加警報對話框時，我的應用程序崩潰。無法弄清原因。警報對話框中有任何錯誤嗎？

日誌條目貓：

06-11 06:02:02.010: W/dalvikvm(3823): threadid=1: thread exiting with uncaught exception (group=0xb2abbba8) 
06-11 06:02:02.040: E/AndroidRuntime(3823): FATAL EXCEPTION: main 
06-11 06:02:02.040: E/AndroidRuntime(3823): Process: com.example.finalassignment, PID: 3823 
06-11 06:02:02.040: E/AndroidRuntime(3823): java.lang.RuntimeException: Unable to start receiver com.example.finalassignment.ConnectionReciever: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.app.ActivityThread.handleReceiver(ActivityThread.java:2426) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.app.ActivityThread.access$1700(ActivityThread.java:135) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1272) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.os.Handler.dispatchMessage(Handler.java:102) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.os.Looper.loop(Looper.java:136) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.app.ActivityThread.main(ActivityThread.java:5017) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at java.lang.reflect.Method.invokeNative(Native Method) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at java.lang.reflect.Method.invoke(Method.java:515) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at dalvik.system.NativeStart.main(Native Method) 
06-11 06:02:02.040: E/AndroidRuntime(3823): Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.view.ViewRootImpl.setView(ViewRootImpl.java:540) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:259) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.app.Dialog.show(Dialog.java:286) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at com.example.finalassignment.ConnectionReciever.onReceive(ConnectionReciever.java:25) 
06-11 06:02:02.040: E/AndroidRuntime(3823):  at android.app.ActivityThread.handleReceiver(ActivityThread.java:2419) 

Answer 1

問題是與活動場景。您需要傳遞活動的上下文以顯示對話框。

Answer 2

Context作爲參數傳遞給onReceive() is-a ReceiverRestrictedContext。

要顯示對話框，您需要一個Context即-al Activity。

要顯示來自廣播接收器的通知，請使用Notification而不是對話框。

如果您在清單中註冊了收件人，請勿嘗試向其傳遞Activity引用。一旦onReceive()返回，系統可以自由地終止進程 - 您不能在那裏執行任何異步操作（例如Dialog）。

Answer 3

在我的情況下，如果添加彈出式窗口或對話框時父視圖尚未準備好顯示並且視圖尚未附加到窗口，可能會發生這種情況。

解決的辦法是在觸發彈出菜單/對話框或延遲幾百毫秒彈出窗口之前，檢查視圖是否附加到窗口。

希望它有幫助。

Answer 4

: Unable to add window -- token null is not for an application 

在操作系統無法決定與哪個活動相關的窗口調用時發生，在此情況下爲警報對話框。現在，您正在嘗試使用從廣播接收器傳遞的上下文，該上下文仍然不會指示警報對話框應該附加到哪個活動。相反，在警報對話框中使用MyActivity.this作爲上下文，一切都會正常工作。

修改代碼：

public class ConnectionReciever extends BroadcastReceiver { 

@Override 
public void onReceive(Context context, Intent intent) { 
    ConnectivityManager connectivityManager = (ConnectivityManager) context 
      .getSystemService(Context.CONNECTIVITY_SERVICE); 
    NetworkInfo activeNetwork = connectivityManager.getActiveNetworkInfo(); 
    if (activeNetwork != null && activeNetwork.isConnected()) { 
//   Toast.makeText(context, "Internet Connection is Active", 
//     Toast.LENGTH_LONG).show(); 

     AlertDialog.Builder alertDialog = new AlertDialog.Builder(MyActivity.this); 
     // Replace MyActivity with your activity name in MyActivity.this 
     alertDialog.setMessage("Internet Connection is Active"); 
     alertDialog.show(); 

    } else { 
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(MyProfile.this); 
     // Replace MyActivity with your activity name in MyActivity.this 
     alertDialog.setMessage("Internet Connection Timed Out....Please try again"); 
     alertDialog.show(); 

    } 

} 
}