应用程序在前台时无法处理FCM通知

public class MyFirebaseMessagingService extends FirebaseMessagingService {
    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        if (remoteMessage.getData().size() > 0) {
            // 处理数据消息
        }
        if (remoteMessage.getNotification() != null) {
            // 处理通知消息
            String title = remoteMessage.getNotification().getTitle();
            String body = remoteMessage.getNotification().getBody();
            // 显示通知
            sendNotification(title, body);
        }
    }

    private void sendNotification(String title, String messageBody) {
        Intent intent = new Intent(this, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent,
                PendingIntent.FLAG_ONE_SHOT);

        String channelId = "fcm_default_channel";
        NotificationCompat.Builder builder =
                new NotificationCompat.Builder(this, channelId)
                        .setSmallIcon(R.drawable.ic_notification)
                        .setContentTitle(title)
                        .setContentText(messageBody)
                        .setAutoCancel(true)
                        .setContentIntent(pendingIntent);

        NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(channelId,
                    "Channel human readable title",
                    NotificationManager.IMPORTANCE_DEFAULT);
            notificationManager.createNotificationChannel(channel);
        }
        notificationManager.notify(0, builder.build());
    }
}

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />

<permission
    android:name="your.package.name.permission.C2D_MESSAGE"
    android:protectionLevel="signature" />

<uses-permission android:name="your.package.name.permission.C2D_MESSAGE" />