NotificationChannel issue in Android O

As it is written in Android Documentation:

https://developer.android.com/preview/features/notification-channels.html

If you target Android O and post a notification without specifying a valid notifications channel, the notification fails to post and the system logs an error.

To solve this issue you need to create a NotificationChannel.

NotificationManager mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);// The id of the channel.String id = "my_channel_01";// The user-visible name of the channel.CharSequence name = getString(R.string.channel_name);// The user-visible description of the channel.String description = getString(R.string.channel_description);int importance = NotificationManager.IMPORTANCE_LOW;NotificationChannel mChannel = new NotificationChannel(id, name,importance);// Configure the notification channel.mChannel.setDescription(description);mChannel.enableLights(true);// Sets the notification light color for notifications posted to this// channel, if the device supports this feature.mChannel.setLightColor(Color.RED);mChannel.enableVibration(true);mChannel.setVibrationPattern(new long[]{100, 200, 300, 400, 500, 400, 300, 200, 400});mNotificationManager.createNotificationChannel(mChannel);

And then assign it to your Notification like this:

mNotificationManager = (NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);// Sets an ID for the notification, so it can be updated.int notifyID = 1;// The id of the channel.String CHANNEL_ID = "my_channel_01";// Create a notification and set the notification channel.Notification notification = new Notification.Builder(MainActivity.this)    .setContentTitle("New Message")    .setContentText("You've received new messages.")    .setSmallIcon(R.drawable.ic_notify_status)    .setChannelId(CHANNEL_ID)    .build();// Issue the notification.mNotificationManager.notify(id, notification);

Update:

In case you want to use NotificationCompat here is a simple example:

NotificationCompat.Builder mBuilder;mBuilder = new NotificationCompat.Builder(getApplicationContext())    .setSmallIcon(R.mipmap.ic_launcher_icon)    .setContentTitle("Title")    .setContentText("Text")    .setOngoing(true)    .setChannelId(id);

In fact you have to use Notification Builder in order to set channel id via setChannelId();

Messages on Toast and Logcat talk about you should be paid attention to 2 items and them order:

1. NotificationChannel mChannel = new NotificationChannel(id, name, importance);
2. builder = new NotificationCompat.Builder(this, id);

Also NotificationManager notifManager and NotificationChannel mChannel are created only once.

There are required setters for Notification:

builder.setContentTitle() // required         .setSmallIcon()    // required        .setContentText()  // required  

See the example in On Android 8.1 API 27 notification does not display.