NotificationService类

public class NotificationService extends Service {
    private Notification notification;
    private PendingIntent pit;
    private NotificationManager notificationManager;
    public NotificationService() {
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Intent it = new Intent(this, MainActivity.class);
//        it.putExtra("NotificationService","SUCCESS");
        pit = PendingIntent.getActivity(this, 0, it, 0);
        notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        Notification.Builder mBuilder=new Notification.Builder(this);
        mBuilder.setSmallIcon(R.drawable.ic_launcher_background)
                .setContentTitle("预警信息")//标题
                .setContentText("1111")
                .setWhen(System.currentTimeMillis())           //设置通知时间
                .setAutoCancel(true)                           //设置点击后取消Notification
                .setContentIntent(pit);
        notification = mBuilder.build();
        notificationManager.notify(1,notification);
    }
}

MainActivity类

public class MainActivity extends AppCompatActivity {

    private AlarmManager manager;
    private PendingIntent pi;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        manager= (AlarmManager) getSystemService(ALARM_SERVICE);
        Intent intent = new Intent(this, NotificationService.class);
        pi = PendingIntent.getService(this, 0, intent, 0);
        // 设置AlarmManager启动与时间间隔(低于一分钟会以一分钟计算)
        manager.setRepeating(AlarmManager.RTC_WAKEUP, AlarmManager.RTC,300000L, pi);
    }
}