创建通知管理器时出现空指针异常

如何解决创建通知管理器时出现空指针异常

当我尝试启动服务时，我收到一个空指针异常，这是由实例化通知管理器引起的。这看起来相当简单，只是实例化，但这一行代码导致应用程序崩溃。

这个问题的原因是什么？

在 onStop 方法中启动服务：

@Override
    protected void onStop() {
        super.onStop();
        Intent notifService = new Intent(getApplicationContext(),NotificationService.class);
        startService(notifService);
    }

服务类：

package ch.zli.eb.myfitnessjourney.service;


public class NotificationService extends Service {
    private String channelId = "myfitnessjourney_1";
    private int notificationId = 101;

    notificationmanager notifManager = getSystemService(notificationmanager.class);

    private LocalBinder mybinder = new LocalBinder();

    private Timer notifTimer;
    private TimerTask notifTimerTask;

    private final int intervalSec = 5;

    private Handler notifHandler;


    public NotificationService() throws ParseException {
        createNotificationChannel();
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mybinder;
    }


    @Override
    public int onStartCommand(Intent intent,int flags,int startId) {
        super.onStartCommand(intent,flags,startId);

        try {
            startTimer();
        } catch (ParseException e) {
            e.printstacktrace();
        }

        return START_STICKY;
    }


    @Override
    public void onCreate() {
    }

    @Override
    public void onDestroy() {
        stopTimerTask();
        super.onDestroy();
    }

    public void startTimer() throws ParseException {
        notifTimer = new Timer();

        initializeTimerTask();

        notifTimer.schedule(notifTimerTask,5000,intervalSec * 1000);
    }

    public void stopTimerTask() {
        if (notifTimer != null) {
            notifTimer.cancel();
            notifTimer = null;
        }
    }

    public void initializeTimerTask() throws ParseException {
        DbManager dbManager = new DbManager(this);
        ArrayList<Goal> goalList = dbManager.getGoals();

        // required DATE FORMAT
        DateFormat dateFormatter = new SimpleDateFormat("dd.MM.yyyy");
        dateFormatter.setLenient(false);
        Date todaysDate = dateFormatter.parse(dateFormatter.format(new Date()));

        notifTimerTask = new TimerTask() {
            public void run() {
                notifHandler = new Handler();
                notifHandler.post(new Runnable() {
                    public void run() {
                        for (Goal g : goalList) {
                            if (g.isReminders()) {
                                if (g.getEndDate().compareto(todaysDate) == 0) {
                                    sendNotification(g);
                                }
                            }
                        }

                    }
                });
            }
        };
    }

    private void createNotificationChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            String notifTitle = "Title";
            String notifDesc = "Description";
            int importance = notificationmanager.IMPORTANCE_DEFAULT;

            NotificationChannel notifChannel = new NotificationChannel(channelId,notifTitle,importance);
            notifManager.createNotificationChannel(notifChannel);
        }
    }

    private void sendNotification(Goal g) {
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this,channelId)
                .setContentTitle("Goal Deadline")
                .setContentText(g.getName() + "is about to pass the deadline!")
                .setPriority(NotificationCompat.PRIORITY_DEFAULT);

        notifManager.notify(notificationId,builder.build());
    }

    public class LocalBinder extends Binder {
        NotificationService getService() {
            return NotificationService.this;
        }
    }
}

解决方法

getSystemService(Class serviceClass) 是抽象类Context的一个方法。因此，如果您从非活动类调用此方法，则需要将活动类的上下文传递给您的服务类。您可以在构造函数中传递它。

Context mContext;
public NotificationService(Context mContext) {
    this.mContext = mContext;
}

NotificationManager notifManager = mContext.getSystemService(NotificationManager.class);