Windows Portable Devices (WPD) and Events

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

namespace Wpd
{
    internal class PortableDeviceEventCallback : IPortableDeviceEventCallback
    {

        public PortableDeviceEventCallback(PortableDevice device)
        {
            this._device = device;

            this.Register();
        }

        private PortableDevice _device;
        private string _cookie;

        private Guid _eventId;
        public Guid EventId
        {
            get { return _eventId; }
        }

        private string _eventDescription;
        public string EventDescription
        {
            get { return _eventDescription; }
        }

        private string _objectId;
        public string ObjectId
        {
            get { return _objectId; }
        }

        // IPortableDeviceEventCallback Members
        public void OnEvent(IPortableDeviceValues eventParameters)
        {
            eventParameters.GetGuidValue(PropertyKey.WPD_EVENT_PARAMETER_EVENT_ID, out _eventId);

            // Convert the CLSID to a string.
            _eventDescription = NativeMethods.StringFromCLSID(_eventId);

            eventParameters.GetStringValue(PropertyKey.WPD_OBJECT_ID, out _objectId);
        }
        
        /// <summary>
        /// IPortableDevice.Advise is used to register for event notifications
        /// This returns a cookie string that is needed while unregistering.
        /// </summary>
        public void Register()
        {
            PortableDeviceValues eventParameters = new PortableDeviceValues();

            _device.Advise(0, this, eventParameters, out _cookie);
        }

        public void Unregister()
        {
            if (string.IsNullOrEmpty(_cookie))
                throw new NullReferenceException("Invalid event cookie");

            _device.Unadvise(_cookie);

            Marshal.ReleaseComObject(this);
        }

    }
}

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