所以，我有一个应用程序，每小时检查一个文本文件的更改.如果它发现更改，它需要给给予推送通知.但当我测试了一天的应用程序，它只工作的第一次.每隔一段时间，它只发生在我打开应用程序时inmediatly.我的curent代码如下：
主要活动：
on create

notificationManager = NotificationManagerCompat.from(this);

        // sets time for when to notify/ check for rescheduling.
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY, 20);
        calendar.set(Calendar.MINUTE, 01);
        calendar.set(Calendar.SECOND, 00);

        setAlarm(calendar);

字符串
设置报警

@RequiresApi(api = Build.VERSION_CODES.KITKAT)
    private void setAlarm(Calendar calendar) {

        AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        Intent intent = new Intent(this, AlarmReceiver.class);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 1, intent, 0);

        alarmManager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
    }

型
报警接收器：

public class AlarmReceiver extends BroadcastReceiver {

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

        NotificationHelper notificationHelper = new NotificationHelper(context);
        NotificationCompat.Builder nb = notificationHelper.getChannelNotification();
        notificationHelper.getManager().notify(1, nb.build());
    }
}

型
NotificationHelper：

public class NotificationHelper extends ContextWrapper {
    public static final String channelID = "Chanel1";
    public static final String channelName = "Probably change";

    private NotificationManager mManager;

    public NotificationHelper(Context base) {
        super(base);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            createChannel();
        }
    }

    @TargetApi(Build.VERSION_CODES.O)
    private void createChannel() {
        NotificationChannel channel1 = new NotificationChannel(channelID, channelName, NotificationManager.IMPORTANCE_HIGH);
        channel1.enableLights(true);
        channel1.setLightColor(R.color.colorPrimary);
        channel1.setLockscreenVisibility(Notification.VISIBILITY_PUBLIC);
        channel1.setImportance(NotificationManager.IMPORTANCE_HIGH);

        getManager().createNotificationChannel(channel1);
    }

    public NotificationManager getManager() {
        if (mManager == null) {
            mManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        }

        return mManager;
    }

    public NotificationCompat.Builder getChannelNotification(){
        return new NotificationCompat.Builder(getApplicationContext(), channelID)
                .setContentTitle("Schedule change")
                .setContentText("There is probably a change in schedule for your class.")
                .setSmallIcon(R.drawable.ic_launcher_foreground);
    }
}

型