package user.example.test;

import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.NotificationCompat;
import androidx.core.app.NotificationManagerCompat;

import android.app.AlertDialog.*;
import android.app.Dialog;
import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Build;
import android.view.*;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @RequiresApi(api = Build.VERSION_CODES.M)
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Notification.Builder builder = new Notification.Builder(this)
                .setSmallIcon(R.mipmap.ic_launcher_round)
                .setContentTitle("標題")
                .setContentText("訊息內容")
                .setAutoCancel(true);
        NotificationChannel channel = new NotificationChannel("channel_1", "123", NotificationManager.IMPORTANCE_LOW);
        NotificationManager notifyManger = (NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);
        notifyManger.createNotificationChannel(channel);
        notifyManger.notify(1, builder.build());
    }
}

new NotificationChannel會顯示紅色