Android 8.0通知需要设置通知渠道才能正常显示，步骤如下：

*官方创建通知文档：https://developer.android.google.cn/training/notify-user/build-notification

1、定义通知id、通知渠道id、通知渠道名

 private static final int PUSH_NOTIFICATION_ID = (0x001);
    private static final String PUSH_CHANNEL_ID = "PUSH_NOTIFY_ID";
    private static final String PUSH_CHANNEL_NAME = "PUSH_NOTIFY_NAME";

注：a.通知渠道id不能太长且在当前应用中是唯一的，太长会被截取。官方说明：

The id of the channel. Must be unique per package. The value may be truncated if it is too long.

        b.通知渠道名也不能太长推荐40个字符，太长同样会被截取。官方说明：

The recommended maximum length is 40 characters; the value may be truncated if it is too long.

2、创建通知渠道 Android8.0

 NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(PUSH_CHANNEL_ID, PUSH_CHANNEL_NAME, NotificationManager.IMPORTANCE_HIGH);
            if (notificationManager != null) {
                notificationManager.createNotificationChannel(channel);
            }
        }

3.发送通知标题 ，内容并显示

 NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
        Intent notificationIntent = new Intent(this, MainActivity.class);
        notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
        builder.setContentTitle("通知标题")//设置通知栏标题
                .setContentIntent(pendingIntent) //设置通知栏点击意图
                .setContentText("通知内容")
                .setTicker("通知内容") //通知首次出现在通知栏，带上升动画效果的
                .setWhen(System.currentTimeMillis())//通知产生的时间，会在通知信息里显示，一般是系统获取到的时间
                .setSmallIcon(R.mipmap.ic_launcher)//设置通知小ICON
                .setChannelId(PUSH_CHANNEL_ID)
                .setDefaults(Notification.DEFAULT_ALL);

        Notification notification = builder.build();
        notification.flags |= Notification.FLAG_AUTO_CANCEL;
        if (notificationManager != null) {
            notificationManager.notify(PUSH_NOTIFICATION_ID, notification);
        }