Android 8.0通知需要設定通知渠道才能正常顯示，步驟如下：

1、定義通知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不能太長且在當前應用中是唯一的，太長會被擷取。官方說明：

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長推薦40個字元，太長同樣會被擷取。官方說明：

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

2、建立通知渠道

NotificationManager notificationManager = (NotificationManager) context.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、建立通知並顯示

NotificationCompat.Builder builder = new NotificationCompat.Builder(context);
 
Intent notificationIntent = new Intent(context, MainActivity.class);
notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, notificationIntent, 0);
builder.setContentTitle("通知標題")//設定通知欄標題
.setContentIntent(pendingIntent) //設定通知欄點選意圖
.setContentText("通知內容")
        .setNumber(++pushNum)
        .setTicker("通知內容") //通知首次出現在通知欄，帶上升動畫效果的
.setWhen(System.currentTimeMillis())//通知產生的時間，會在通知資訊裡顯示，一般是系統獲取到的時間
.setSmallIcon(R.mipmap.ic_launcher)//設定通知小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);
}

NotificationCompat.Builder builder = new NotificationCompat.Builder(context);

NotificationCompat.Builder builder = new NotificationCompat.Builder(context,PUSH_CHANNEL_ID);