即使通知管理器已正確初始化，也無法創建通知

Question

我試圖使用Android中的NotificationManager API發送通知。下面是我的代碼：

的AndroidManifest.xml：

<uses-sdk 
    android:minSdkVersion="23" 
    android:targetSdkVersion="23" /> 
<uses-permission android:name="android.permission.INTERNET" /> 
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> 
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> 
... 
    <activity 
     android:name="com.tabs.activity.Comments" 
     android:configChanges="orientation|keyboardHidden" 
     android:label="View Post" 
     android:theme="@style/AppTheme.NoActionBar" 
     android:windowSoftInputMode="stateAlwaysHidden|adjustResize" > 
    </activity> 
    <service 
     android:name="com.tabs.activity.NotificationService"> 
     <intent-filter> 
      <action android:name="com.google.firebase.MESSAGING_EVENT"/> 
     </intent-filter> 
    </service> 
... 

Comments.java：

public void createComment(){ 
    ... 
    NotificationService notificationService = new NotificationService(); 
    notificationService.showNotification(getApplicationContext(), R.id.commenter_profile_photo, "User commented: Hi!", "User"); 
    ... 
} 

NotificationService.java：所顯示

public void showNotification(Context context, int commenterId, String messageBody, String commenter){ 
    NotificationCompat.Builder notifiationBuilder = new NotificationCompat.Builder(this) 
      .setContentTitle("Title") 
      .setContentText(messageBody) 
      .setTicker("New comment from " + commenter) 
      .setSmallIcon(commenterId); 

    Intent moreInfoIntent = new Intent(context, news_feed.class); 

    //When the user clicks back, it doesn't look sloppy! 
    TaskStackBuilder taskStackBuilder = TaskStackBuilder.create(context); 
    taskStackBuilder.addNextIntent(moreInfoIntent); 

    //If the intent already exists, just update it and not create a new one 
    PendingIntent pendingIntent = taskStackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT); 

    //When the notification is actually clicked on 
    notifiationBuilder.setContentIntent(pendingIntent); 

    //Notification manager to notify of background event 
    notificationManager = (NotificationManager) context.getSystemService(NOTIFICATION_SERVICE); 

    notificationManager.notify(1, notifiationBuilder.build()); 
} 

錯誤（堆棧跟蹤） ：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference 
                  at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:160) 
                  at android.app.Notification$Builder.<init>(Notification.java:2287) 
                  at android.support.v4.app.NotificationCompatApi21$Builder.<init>(NotificationCompatApi21.java:68) 
                  at android.support.v4.app.NotificationCompat$NotificationCompatImplApi21.build(NotificationCompat.java:759) 
                  at android.support.v4.app.NotificationCompat$Builder.build(NotificationCompat.java:1559) 
                  at com.tabs.activity.NotificationService.showNotification(NotificationService.java:113) 
                  at com.tabs.activity.Comments.createComment(Comments.java:146) 

此代碼的問題是，無論出於何種原因，notificationManager.notify(1, notifiationBuilder.build());行總是會生成NullPointerException。我知道他們是什麼，但我似乎無法解決這個問題，因爲我不明白爲什麼我的背景需要getApplicationInfo()。當我從Comments.java傳遞給我時，我的上下文應該已經有了。我只是不明白我該如何錯誤地構建通知管理器。以下是給出的堆棧跟蹤。任何幫助，將不勝感激。謝謝！

Answer 1

變化

NotificationCompat.Builder notifiationBuilder = new NotificationCompat.Builder(this) 

到

NotificationCompat.Builder notifiationBuilder = new NotificationCompat.Builder(context)