未触发警报且未显示通知

Question

我正在尝试设置每天上午8点的闹钟，以便它可以显示一些通知 这是我设置闹钟的方法：

public static void scheduleAlarm(Context context) {
    PackageManager pm = context.getPackageManager();
    ComponentName receiver = new ComponentName(context, DeviceBootReceiver.class);
    Intent alarmIntent = new Intent(context, AlarmReceiver.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, alarmIntent, 0);
    AlarmManager manager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);

        //region Enable Daily Notifications
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(System.currentTimeMillis());
        calendar.set(Calendar.HOUR_OF_DAY, 8);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        // if notification time is before selected time, send notification the next day
        if (calendar.before(Calendar.getInstance())) {
            calendar.add(Calendar.DATE, 1);
        }
        if (manager != null) {
            manager.setInexactRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                    AlarmManager.INTERVAL_DAY, pendingIntent);
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                manager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
            }
        }
        //To enable Boot Receiver class
        pm.setComponentEnabledSetting(receiver,
                PackageManager.COMPONENT_ENABLED_STATE_ENABLED,
                PackageManager.DONT_KILL_APP);
}

我已为android O设置了频道，仍然没有通知。 有人可以在下面的代码中说明问题所在吗？ 警报接收器类别以显示通知：

 public class AlarmReceiver extends BroadcastReceiver {
@Overridepublic void onReceive(Context context, Intent intent) {

    NotificationManager nm = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    Intent notificationIntent = new Intent(context, MainActivity.class);

    notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
            | Intent.FLAG_ACTIVITY_SINGLE_TOP);

    PendingIntent pendingI = PendingIntent.getActivity(context, 0,
            notificationIntent, 0);
    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
        NotificationChannel channel = new NotificationChannel("default",
                "Daily Notification",
                NotificationManager.IMPORTANCE_DEFAULT);
        channel.setDescription("Daily Notification");
        if (nm != null) {
            nm.createNotificationChannel(channel);
        }
    }
    NotificationCompat.Builder b = new NotificationCompat.Builder(context, "default");
    b.setAutoCancel(true)
            .setDefaults(NotificationCompat.DEFAULT_ALL)
            .setWhen(System.currentTimeMillis())
            .setSmallIcon(R.drawable.ic_launcher)
            .setTicker("{Time to watch some cool stuff!}")
            .setContentTitle("My Cool App")
            .setContentText("Time to watch some cool stuff!")
            .setContentInfo("INFO")
            .setContentIntent(pendingI);


}}