Base Class ViewModel (using Fresh MVVM) for working with NFC

NfcViewModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using bmx.Contract;
using bmx.Contract.EventArgs;

namespace bmx.ViewModels
{
    abstract class NfcViewModel : ViewModelBase
    {
        protected INfcService NfcService { get; set; }

        public override void Init(object initData)
        {
            NfcService = Resolve<INfcService>();
            base.Init(initData);
        }

        private CancellationTokenSource _source = new CancellationTokenSource();

        protected override void ViewIsAppearing(object sender, EventArgs e)
        {
            _source.Cancel();
            _source = new CancellationTokenSource();
            NfcService.NfcFound -= HandleNfc;
            NfcService.NfcFound += HandleNfc;
            base.ViewIsAppearing(sender, e);
        }

        protected override void ViewIsDisappearing(object sender, EventArgs e)
        {
            base.ViewIsDisappearing(sender, e);
            Task.Delay(500, _source.Token)
                .ContinueWith((task, obj) => HandleDisconnect(task.IsCanceled), null);

        }

        private void HandleDisconnect(bool cancelled) // disconnect event if navigated away
        {
            // this method is required becuase reading an NFC tag 'temporarily' makes the view dissappear and appear, meaning we can't naiivly disconnect the event
            if (!cancelled)
            {
                NfcService.NfcFound -= HandleNfc;
            }

        }
        protected abstract void HandleNfc(object sender, NfcEventArgs e);


    }
}