使用 Firebase 使用 xamarin 表单进行用户存在跟踪

Question

我正在使用 firebase 在我的应用上跟踪我的设备。当我的设备上的网络断开连接时，我想在 firebase 上通知。根据以下链接， https://firebase.google.com/docs/database/android/offline-capabilities 我正在使用以下代码：

#if __ANDROID__
FirebaseDatabase firebase = FirebaseDatabase.Instance;
FirebaseDatabase.Instance.SetPersistenceEnabled(true);
                var userListRef = firebase.GetReference("USERS_ONLINE");
                var myUserRef = userListRef.Push();
                DatabaseReference connectedRef = firebase.GetReference(".info/connected");

                connectedRef.AddValueEventListener(new ValueEventListener());

ValueEventListener 类：

internal class ValueEventListener : Java.Lang.Object, IValueEventListener
    {
       // public IntPtr Handle => throw new NotImplementedException();

        public void Dispose()
        {
            throw new NotImplementedException();
        }

        public void OnCancelled(DatabaseError error)
        {
            throw new NotImplementedException();
        }

        public void OnDataChange(DataSnapshot snapshot)
        {
            FirebaseDatabase firebase = FirebaseDatabase.Instance;
            DatabaseReference myConnectionsRef = firebase.GetReference("users/joe/connections");
                        bool connected =  Convert.ToBoolean(snapshot.GetValue(true));
            myConnectionsRef.KeepSynced(true);

            if (connected)
            {
                DatabaseReference con = myConnectionsRef.Push();
                con.OnDisconnect().RemoveValue();
                myConnectionsRef.SetValue(Boolean.TrueString);
            }
            else
            {
                DatabaseReference con = myConnectionsRef.Push();
                con.OnDisconnect().RemoveValue();
                myConnectionsRef.SetValue(Boolean.FalseString);
            }
        }
    }

但它仅在仅在线时才有效。谁能帮我解决这个问题。

Answer 1

在我的 xaml.cs 文件中：

#if __ANDROID__
                string myConnectionsRefNode = "users/Truckers/Joe/connections";
                Constants.connectedRef = FirebaseDatabase.Instance.GetReference(".info/connected");
                Constants.myConnectionsRef = FirebaseDatabase.Instance.GetReference(myConnectionsRefNode);
                Constants.connectedRef.AddValueEventListener(new MyProject.Droid.Services.ValueEventListener());

#elif __IOS__
                var context = AppDelegate.Instance;
                if(context!=null)
        {
                    context.FCMOfflineAccess();
                }
#endif

在 Constants.cs 文件中：

public static bool IsFCMOffline = true;
public static DatabaseReference connectedRef;
public static DatabaseReference myConnectionsRef;

在 Droid/ValueEventListener.cs 文件中：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Firebase.Database;
using MyProject.Common;
namespace MyProject.Droid.Services
{
    public class ValueEventListener : Java.Lang.Object, IValueEventListener
    {
        public void OnCancelled(DatabaseError error)
        {
            throw new NotImplementedException();
        }

        public void OnDataChange(DataSnapshot snapshot)
        {
            DatabaseReference con = Constants.myConnectionsRef.Ref;
            con.OnDisconnect().SetValue("Offline");
            con.SetValue("Online");
        }
    }
}

在 iOS/AppDelegate.cs 文件中：

public void FCMOfflineAccess()
        {
                var connectedRef = Database.DefaultInstance;
                var MyConnectedRef = connectedRef.GetReferenceFromPath("users/Truckers/" + TruckerId);
                var connectedRef1 = connectedRef.GetReferenceFromPath(".info/connected");
                connectedRef1.ObserveEvent(DataEventType.Value, HandleAction);
        }

        private void HandleAction(DataSnapshot snapshot)
        {
            try
            {
                var connectedRef = Database.DefaultInstance;
                var con = connectedRef.GetReferenceFromPath("users/Truckers/Joe");

                string[] statOffline = { "Offline" };
                string[] keyOffline = { "connections" };
                var dataOffline = NSDictionary.FromObjectsAndKeys(statOffline, keyOffline, keyOffline.Length);
                con.SetValueOnDisconnect(dataOffline);

                string[] statOnline = { "Online" };
                string[] keyOnline = { "connections" };
                var dataOnline = NSDictionary.FromObjectsAndKeys(statOnline, keyOnline, keyOnline.Length);
                con.SetValue(dataOnline);

            }
            catch (Exception ex)
            {

            }
        }