如何正确显示通知？

Question

我一直在研究如何在Android上显示通知，但我不知道为什么它根本不显示通知。

在主要活动的onCreate（）中调用此方法

private void scheduleNotification(){
        AlarmManager alarmMgr = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        Intent alarmIntent = new Intent(this, NotificationObject.class);
        PendingIntent alarmPendingIntent = PendingIntent.getBroadcast(this, 0, alarmIntent, PendingIntent.FLAG_UPDATE_CURRENT);
        Date date = new Date();
        long timestamp = date.getTime();
        SimpleDateFormat df = new SimpleDateFormat("HH:mm:ss", Locale.getDefault());
        alarmMgr.setExact(AlarmManager.RTC_WAKEUP, timestamp + 5000, alarmPendingIntent);
    }

这是我的通知对象

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

    private void createNotification(Context context, Intent fromIntent) {
        NotificationManager nm = (NotificationManager) context.getSystemService(NOTIFICATION_SERVICE);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel notificationChannel = new NotificationChannel(NOTIFICATION_CHANNEL_ID, "Weather Notifications", NotificationManager.IMPORTANCE_DEFAULT);

            // Configure the notification channel.
            notificationChannel.setDescription("Channel description");
            notificationChannel.enableLights(true);
            notificationChannel.setLightColor(Color.RED);
            notificationChannel.setVibrationPattern(new long[]{0, 1000, 500, 1000});
            notificationChannel.enableVibration(true);
            nm.createNotificationChannel(notificationChannel);
        }

        Log.d("NOTIFICATION", "I'm in notification");
        WeatherApiCall weatherApiCall = new WeatherApiCall();
        String weatherInfo = weatherApiCall.getWeatherInfo("weather", "Iasi,ro", "metric");
        String temperatureText = null;
        JSONObject weatherApiResult;
        try {
            weatherApiResult = new JSONObject(weatherInfo);
            temperatureText = "Temperature: " + weatherApiResult.getJSONObject("main").getDouble("temp") + " \u00B0C";
            Log.d("NOTIFICATION", temperatureText);
        } catch (JSONException e) {
            e.printStackTrace();
        }

        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID)
                .setSmallIcon(R.drawable.sun)
                .setWhen(System.currentTimeMillis())
                .setContentTitle(temperatureText)
                .setContentText(temperatureText)
                .setPriority(NotificationCompat.PRIORITY_DEFAULT);

        nm.notify(NOTIFICATION_ID, notificationBuilder.build());
    }