Busy State Manager - WPF helper (mini framework) for managing IsBusy state

BusyStateManager.cs

// BusyStateManager usings
using System.Collections.Generic;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Messaging;
using Savaged.Info.Desktop.Messages;

// BusyMessage usings
using System;
using System.Runtime.CompilerServices;
using GalaSoft.MvvmLight.Messaging;

namespace Savaged.Info.Desktop.Helpers
{
    /// <summary>
    /// A Boolean value for busy which should be used in conjunction with
    /// the XCeed Toolkit BusyIndicator or similar control. This class is
    /// responsible for managing this state which can be problematic if
    /// it is just being set in process because different threads can set
    /// it prior to other threads completing. A better solution is to have
    /// this central static register of running threads, which unregister 
    /// once complete, then the busy value is only set to true once the 
    /// register is empty.
    /// </summary>
    public class BusyStateManager : ObservableObject
    {
        private IList<string> _registry;

        public BusyStateManager()
        {
            _registry = new List<string>();
            Messenger.Default.Register<BusyMessage>(this, OnBusyMessage);
        }

        public bool IsBusy => _registry.Count > 0;

        private void OnBusyMessage(BusyMessage m)
        {
            if (m.IsBusy)
            {
                _registry.Add($"{m.CallerType}.{m.CallerMember}");
            }
            else
            {
                _registry.Remove($"{m.CallerType}.{m.CallerMember}");
            }
            RaisePropertyChanged(nameof(IsBusy));
        }
    }
}


// This can be put in a different file if you like
namespace Savaged.Info.Desktop.Messages
{
    /// <summary>
    /// Message for updating Busy State, used in conjunction with 
    /// Savaged.Info.Desktop.Helpers.BusyStateManager 
    /// </summary>
    /// <example>
    /// Used in conjunction with Savaged.Info.Desktop.Helpers.BusyStateManager 
    /// like this:
    /// <code>
    /// MessengerInstance.Send(new BusyMessage(true, this));
    /// await DoSomthingAsync();
    /// MessengerInstance.Send(new BusyMessage(false, this));
    /// </code>
    /// </example>
    public class BusyMessage : MessageBase
    {
        /// <summary>
        /// ctor
        /// </summary>
        /// <param name="isBusy">The state</param>
        /// <param name="caller">The calling class</param>
        /// <param name="callerMember">The method or property (leave blank because reflection gets this)</param>
        public BusyMessage(bool isBusy, object caller, [CallerMemberName] string callerMember = "")
        {
            IsBusy = isBusy;
            CallerType = caller.GetType();
            CallerMember = callerMember;
        }

        public bool IsBusy { get; }

        public Type CallerType { get; }

        public string CallerMember { get; }
    }
}