Opening multiple document windows with previous instance

using System;
using System.Collections;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Windows.Forms;

namespace vbAccelerator.Components.Win32
{
	public delegate void DataReceivedEventHandler(object sender, DataReceivedEventArgs e);

	/// <summary>
	/// A class which wraps using Windows native WM_COPYDATA
	/// message to send interprocess data between applications.
	/// This is a simple technique for interprocess data sends
	/// using Windows.  The alternative to this is to use
	/// Remoting, which requires a network card and a way
	/// to register the Remoting name of an object so it
	/// can be read by other applications.
	/// </summary>
	public class CopyData : NativeWindow, IDisposable
	{	
		/// <summary>
		/// Event raised when data is received on any of the channels 
		/// this class is subscribed to.
		/// </summary>
		public event DataReceivedEventHandler DataReceived;

		[StructLayout(LayoutKind.Sequential)]
			private struct COPYDATASTRUCT
		{
			public IntPtr dwData;
			public int cbData;
			public IntPtr lpData;
		}
		
		private const int WM_COPYDATA = 0x4A;
		private const int WM_DESTROY = 0x2;

		#region Member Variables
		private CopyDataChannels channels = null;
		private bool disposed = false;
		#endregion

		/// <summary>
		/// Override for a form's Window Procedure to handle WM_COPYDATA
		/// messages sent by other instances of this class.
		/// </summary>
		/// <param name="m">The Windows Message information.</param>
		protected override void WndProc (ref System.Windows.Forms.Message m )
		{
			if (m.Msg == WM_COPYDATA)
			{
				COPYDATASTRUCT cds = new COPYDATASTRUCT();
				cds = (COPYDATASTRUCT) Marshal.PtrToStructure(m.LParam, typeof(COPYDATASTRUCT));
				if (cds.cbData > 0)
				{
					byte[] data = new byte[cds.cbData];				
					Marshal.Copy(cds.lpData, data, 0, cds.cbData);
					MemoryStream stream = new MemoryStream(data);
					BinaryFormatter b = new BinaryFormatter();
					CopyDataObjectData cdo = (CopyDataObjectData) b.Deserialize(stream);
					
					if (channels.Contains(cdo.Channel))
					{
						DataReceivedEventArgs d = new DataReceivedEventArgs(cdo.Channel, cdo.Data, cdo.Sent);
						OnDataReceived(d);
						m.Result = (IntPtr) 1;
					}				
				}
			}
			else if (m.Msg == WM_DESTROY)
			{
				// WM_DESTROY fires before OnHandleChanged and is
				// a better place to ensure that we've cleared 
				// everything up.
				channels.OnHandleChange();
				base.OnHandleChange();
			}
			base.WndProc(ref m);
		}

		/// <summary>
		/// Raises the DataReceived event from this class.
		/// </summary>
		/// <param name="e">The data which has been received.</param>
		protected void OnDataReceived(DataReceivedEventArgs e)
		{
			DataReceived(this, e);
		}

		/// <summary>
		/// If the form's handle changes, the properties associated
		/// with the window need to be cleared up. This override ensures
		/// that it is done.  Note that the CopyData class will then
		/// stop responding to events and it should be recreated once
		/// the new handle has been assigned.
		/// </summary>
		protected override void OnHandleChange ()
		{
			// need to clear up everything we had set.
			channels.OnHandleChange();
			base.OnHandleChange();
		}

		/// <summary>
		/// Gets the collection of channels.
		/// </summary>
		public CopyDataChannels Channels
		{
			get
			{
				return this.channels;
			}
		}

		/// <summary>
		/// Clears up any resources associated with this object.
		/// </summary>
		public void Dispose()
		{
			if (!disposed)
			{
				channels.Clear();
				channels = null;
				disposed = true;
				GC.SuppressFinalize(this);
			}
		}

		/// <summary>
		/// Constructs a new instance of the CopyData class
		/// </summary>
		public CopyData()
		{
			channels = new CopyDataChannels(this);
		}

		/// <summary>
		/// Finalises a CopyData class which has not been disposed.
		/// There may be a minor resource leak if this class is finalised
		/// after the form it is associated with.
		/// </summary>
		~CopyData()
		{
			Dispose();
		}
	}

	/// <summary>
	/// Contains data and other information associated with data
	/// which has been sent from another application.
	/// </summary>
	public class DataReceivedEventArgs
	{
		private string channelName = "";
		private object data = null;
		private DateTime sent;
		private DateTime received;

		/// <summary>
		/// Gets the channel name that this data was sent on.
		/// </summary>
		public string ChannelName
		{
			get
			{
				return this.channelName;
			}
		}
		/// <summary>
		/// Gets the data object which was sent.
		/// </summary>
		public Object Data
		{
			get
			{
				return this.data;
			}
		}
		/// <summary>
		/// Gets the date and time which at the data was sent
		/// by the sending application.
		/// </summary>
		public DateTime Sent
		{
			get
			{
				return this.sent;
			}
		}
		/// <summary>
		/// Gets the date and time which this data item as
		/// received.
		/// </summary>
		public DateTime Received
		{
			get
			{
				return this.received;
			}
		}
		/// <summary>
		/// Constructs an instance of this class.
		/// </summary>
		/// <param name="channelName">The channel that the data was received from</param>
		/// <param name="data">The data which was sent</param>
		/// <param name="sent">The date and time the data was sent</param>
		internal DataReceivedEventArgs(string channelName, object data, DateTime sent)
		{
			this.channelName = channelName;
			this.data = data;
			this.sent = sent;
			this.received = DateTime.Now;
		}
	}

	/// <summary>
	/// A strongly-typed collection of channels associated with the CopyData
	/// class.
	/// </summary>
	public class CopyDataChannels : DictionaryBase
	{
		private NativeWindow owner = null;

		/// <summary>
		/// Returns an enumerator for each of the CopyDataChannel objects
		/// within this collection.
		/// </summary>
		/// <returns>An enumerator for each of the CopyDataChannel objects
		/// within this collection.</returns>
		public new System.Collections.IEnumerator GetEnumerator (  )
		{
			return this.Dictionary.Values.GetEnumerator();
		}

		/// <summary>
		/// Returns the CopyDataChannel at the specified 0-based index.
		/// </summary>
		public CopyDataChannel this[int index]
		{
			get 
			{
				CopyDataChannel ret = null;
				int i = 0;
				foreach (CopyDataChannel cdc in this.Dictionary.Values)
				{
					i++;
					if (i == index)
					{
						ret = cdc;
						break;
					}
				}
				return ret;
			}
		}
		/// <summary>
		/// Returns the CopyDataChannel for the specified channelName
		/// </summary>
		public CopyDataChannel this[string channelName]
		{
			get
			{
				return (CopyDataChannel) this.Dictionary[channelName];
			}
		}
		/// <summary>
		/// Adds a new channel on which this application can send and
		/// receive messages.
		/// </summary>
		public void Add(string channelName)
		{
			CopyDataChannel cdc = new CopyDataChannel(owner, channelName);
			this.Dictionary.Add(channelName , cdc);
		}
		/// <summary>
		/// Removes an existing channel.
		/// </summary>
		/// <param name="channelName">The channel to remove</param>
		public void Remove(string channelName)
		{
			this.Dictionary.Remove(channelName);
		}
		/// <summary>
		/// Gets/sets whether this channel contains a CopyDataChannel
		/// for the specified channelName.
		/// </summary>
		public bool Contains(string channelName)
		{
			return this.Dictionary.Contains(channelName);
		}

		/// <summary>
		/// Ensures the resources associated with a CopyDataChannel
		/// object collected by this class are cleared up.
		/// </summary>
		protected override void OnClear()
		{
			foreach (CopyDataChannel cdc in this.Dictionary.Values)
			{
				cdc.Dispose();
			}
			base.OnClear();
		}

		/// <summary>
		/// Ensures any resoures associated with the CopyDataChannel object
		/// which has been removed are cleared up.
		/// </summary>
		/// <param name="key">The channelName</param>
		/// <param name="data">The CopyDataChannel object which has
		/// just been removed</param>
		protected override void OnRemoveComplete ( Object key , System.Object data )
		{
			( (CopyDataChannel) data).Dispose();
			base.OnRemove(key, data);
		}

		/// <summary>
		/// If the form's handle changes, the properties associated
		/// with the window need to be cleared up. This override ensures
		/// that it is done.  Note that the CopyData class will then
		/// stop responding to events and it should be recreated once
		/// the new handle has been assigned.
		/// </summary>
		public void OnHandleChange()
		{
			foreach (CopyDataChannel cdc in this.Dictionary.Values)
			{
				cdc.OnHandleChange();
			}
		}
		
		/// <summary>
		/// Constructs a new instance of the CopyDataChannels collection.
		/// Automatically managed by the CopyData class.
		/// </summary>
		/// <param name="owner">The NativeWindow this collection
		/// will be associated with</param>
		internal CopyDataChannels(NativeWindow owner)
		{
			this.owner = owner;
		}
	}

	/// <summary>
	/// A channel on which messages can be sent.
	/// </summary>
	public class CopyDataChannel : IDisposable
	{
		#region Unmanaged Code
		[DllImport("user32", CharSet=CharSet.Auto)]
		private extern static int GetProp(
			IntPtr hwnd , 
			string lpString);
		[DllImport("user32", CharSet=CharSet.Auto)]
		private extern static int SetProp(
			IntPtr hwnd , 
			string lpString, 
			int hData);
		[DllImport("user32", CharSet=CharSet.Auto)]
		private extern static int RemoveProp(
			IntPtr hwnd, 
			string lpString);
		
		[DllImport("user32", CharSet=CharSet.Auto)]
		private extern static int SendMessage(
			IntPtr hwnd, 
			int wMsg, 
			int wParam, 				
			ref COPYDATASTRUCT lParam
			);

		[StructLayout(LayoutKind.Sequential)]
		private struct COPYDATASTRUCT
		{
			public IntPtr dwData;
			public int cbData;
			public IntPtr lpData;
		}
		
		private const int WM_COPYDATA = 0x4A;
		#endregion

		#region Member Variables
		private string channelName = "";
		private bool disposed = false;
		private NativeWindow owner = null;
		private bool recreateChannel = false;
		#endregion

		/// <summary>
		/// Gets the name associated with this channel.
		/// </summary>
		public string ChannelName
		{
			get
			{
				return this.channelName;
			}
		}

		/// <summary>
		/// Sends the specified object on this channel to any other
		/// applications which are listening.  The object must have the
		/// SerializableAttribute set, or must implement ISerializable.
		/// </summary>
		/// <param name="obj">The object to send</param>
		/// <returns>The number of recipients</returns>
		public int Send(object obj)
		{
			int recipients = 0;

			if (disposed)
			{
				throw new InvalidOperationException("Object has been disposed");
			}

			if (recreateChannel) // handle has changed
			{
				addChannel();
			}

			CopyDataObjectData cdo = new CopyDataObjectData(obj, channelName);			

			// Try to do a binary serialization on obj.
			// This will throw and exception if the object to
			// be passed isn't serializable.
			BinaryFormatter b = new BinaryFormatter();
			MemoryStream stream = new MemoryStream();
			b.Serialize(stream, cdo);
			stream.Flush();			

			// Now move the data into a pointer so we can send
			// it using WM_COPYDATA:
			// Get the length of the data:
			int dataSize = (int)stream.Length;
			if (dataSize > 0)
			{
				// This isn't very efficient if your data is very large.
				// First we copy to a byte array, then copy to a CoTask 
				// Mem object... And when we use WM_COPYDATA windows will
				// make yet another copy!  But if you're talking about 4K
				// or less of data then it doesn't really matter.
				byte[] data = new byte[dataSize];
				stream.Seek(0, SeekOrigin.Begin);
				stream.Read(data, 0, dataSize);
				IntPtr ptrData = Marshal.AllocCoTaskMem(dataSize);
				Marshal.Copy(data, 0, ptrData, dataSize);

				// Enumerate all windows which have the
				// channel name, send the data to each one
				EnumWindows ew = new EnumWindows();
				ew.GetWindows();

				// Send the data to each window identified on
				// the channel:
				foreach(EnumWindowsItem window in ew.Items)
				{
					if (!window.Handle.Equals(this.owner.Handle))
					{
						if (GetProp(window.Handle, this.channelName) != 0)
						{
							COPYDATASTRUCT cds = new COPYDATASTRUCT();
							cds.cbData = dataSize;
							cds.dwData = IntPtr.Zero;
							cds.lpData = ptrData;
							int res = SendMessage(window.Handle, WM_COPYDATA, (int)owner.Handle, ref cds);
							recipients += (Marshal.GetLastWin32Error() == 0 ? 1 : 0);
						}
					}
				}

				// Clear up the data:
				Marshal.FreeCoTaskMem(ptrData);
			}
			stream.Close();

			return recipients;
		}

		private void addChannel()
		{
			// Tag this window with property "channelName"
			SetProp(owner.Handle, this.channelName, (int)owner.Handle);

		}
		private void removeChannel()
		{
			// Remove the "channelName" property from this window
			RemoveProp(owner.Handle, this.channelName);
		}

		/// <summary>
		/// If the form's handle changes, the properties associated
		/// with the window need to be cleared up. This method ensures
		/// that it is done.  Note that the CopyData class will then
		/// stop responding to events and it should be recreated once
		/// the new handle has been assigned.
		/// </summary>
		public void OnHandleChange()
		{
			removeChannel();
			recreateChannel = true;
		}

		/// <summary>
		/// Clears up any resources associated with this channel.
		/// </summary>
		public void Dispose()
		{
			if (!disposed)
			{
				if (channelName.Length > 0)
				{
					removeChannel();
				}
				channelName = "";
				disposed = true;
				GC.SuppressFinalize(this);
			}
		}

		/// <summary>
		/// Constructs a new instance of a CopyData channel.  Called
		/// automatically by the CopyDataChannels collection.
		/// </summary>
		/// <param name="owner">The owning native window</param>
		/// <param name="channelName">The name of the channel to
		/// send messages on</param>
		internal CopyDataChannel(NativeWindow owner, string channelName)
		{
			this.owner = owner;
			this.channelName = channelName;
			addChannel();
		}

		~CopyDataChannel()
		{
			Dispose();
		}
	}

	/// <summary>
	/// A class which wraps the data being copied, used
	/// internally within the CopyData class objects.
	/// </summary>
	[Serializable()]
	internal class CopyDataObjectData
	{
		/// <summary>
		/// The Object to copy.  Must be Serializable.
		/// </summary>
		public object Data;
		/// <summary>
		/// The date and time this object was sent.
		/// </summary>
		public DateTime Sent;
		/// <summary>
		/// The name of the channel this object is being sent on
		/// </summary>
		public string Channel;

		/// <summary>
		/// Constructs a new instance of this object
		/// </summary>
		/// <param name="data">The data to copy</param>
		/// <param name="channel">The channel name to send on</param>
		/// <exception cref="ArgumentException">If data is not serializable.</exception>
		public CopyDataObjectData(object data, string channel)
		{
			Data = data;
			if (!data.GetType().IsSerializable)
			{
				throw new ArgumentException("Data object must be serializable.", "data");
			}
			Channel = channel;
			Sent = DateTime.Now;
		}
	}

}