android - java.lang.RuntimeException : Unable to start receiver 错误

Question

我是 Android 的初学者。我正在尝试在特定日期显示通知。当我尝试运行 showNotification() 方法时，出现以下错误:

java.lang.RuntimeException: Unable to start receiver com.example.azernax.dforget.ScheduleNotification: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference

我已尝试修复此错误但未成功。

日程通知:

public class ScheduleNotification extends WakefulBroadcastReceiver {

private AlarmManager alarmManager;

@Override
public void onReceive(Context context, Intent intent) {
    ScheduleNotification.completeWakefulIntent(intent);

    //create notification to show !!!
    Toast.makeText(context, "TEST schedule!!!! ", Toast.LENGTH_LONG).show();
    Notification_center notification = new Notification_center();
    notification.showNotification();  //######################### CRASH !!!!
}

通知中心:

public class Notification_center extends AppCompatActivity {

public void showNotification()
{
    NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
    builder.setSmallIcon(R.drawable.icon);
    builder.setContentTitle("dF Notification!");
    builder.setContentText("description"); //--description event--

    Intent intent = new Intent(this, MainActivity.class);
    TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);
    stackBuilder.addParentStack(MainActivity.class);
    stackBuilder.addNextIntent(intent);

    PendingIntent pendingIntent = stackBuilder.getPendingIntent(0,PendingIntent.FLAG_UPDATE_CURRENT);
    builder.setContentIntent(pendingIntent);
    NotificationManager NM = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    NM.notify(0,builder.build());
}

Answer 1

Notification_center notification = new Notification_center();

永远不要自己创建 Activity 的实例，因为它永远无法正常工作。

将代码从 showNotification() 移到 onReceive() 中。您可以使用传递给 onReceive() 的 Context 替代 this 和调用 getSystemService().

另外，这里你不需要WakefulBroadcastReceiver。这适用于您需要将工作委托(delegate)给其他东西的情况(例如，IntentService)。如果所有工作都在 onReceive() 结束时完成，则不需要管理单独的 WakeLock，这就是 WakefulBroadcastReceiver 是为了。