SILVERLIGHT APPLICATION : VBSL3LocalMessage Project Overview

Use:


This project create a whiteboard application demonstrating how to use local message
in silverlight 3. To test this local messaging sample, open TestPage.html in two
browsers, draw on one of the application, another one would keep synchronous.

Prerequisites:


Silverlight 3 Tools for Visual Studio 2008 SP1
http://www.microsoft.com/downloads/details.aspx?familyid=9442b0f2-7465-417a-88f3-5e7b5409e9dd&displaylang=en

Silverilght 3 runtime:
http://silverlight.net/getstarted/

Code Logic:


1. How does this sample working?
   1. When starting application, use localmessagereceiver and localmessagesender
      to create a duplex communication channel.
   2. When drawing a stroke, serialize stroke object to a string, use localmessagesender
      send string to another applciation.
   3. When localmessagereceiver received stroke string, deserialize to stroke object,
      add to InkPresenter.

2. How to establish duplex communication channel between two application?
   1. Preassign two names as LocalMessageReceiver name.
   2. Use one of its name to create LocalMessageReeciver, register messagereceived event,
      start listening by calling LocalMessageRecevier.Listen(). if got exception, it means
      another application with same name in domain has started listening already, try use
      another preset name to create receiver.
   3. When initializing LocalMessageReceiver successful, create LocalMessageSender targeting
      to another application's recever. Register messagesended event, handling the message send
      state and response message there.

3. How to serialize/deserialize object for transfering by local message?
   Local message only accept text format message, to transfer object, we could use Xml or JSON
   Serializer. This sample use DataContractJsonSerializer to serialize/deserialize object.
   To serialize Stroke object to json string:
   
       ' Serialize stroke object to string.
       Dim stream As New MemoryStream
       Me._jsonserializer.WriteObject(stream, Me._newStroke)
       stream.Flush()
       stream.Position = 0
       Dim obstring As String = New StreamReader(stream).ReadToEnd
       stream.Close()
       
   To deserialize string to Stroke object:
   
       ' Deserialize json string to stroke object.
       Dim stream As New MemoryStream
       Dim streamwriter As New StreamWriter(stream)
       streamwriter.Write(e.Message)
       streamwriter.Flush()
       Dim receivedstroke As Stroke = TryCast(Me._jsonserializer.ReadObject(stream), Stroke)
       stream.Close()
   
   For details about DataContractJsonSerializer, please check msdn article
   http://msdn.microsoft.com/en-us/library/system.runtime.serialization.json.datacontractjsonserializer(VS.95).aspx
   
4. How to use implement drawing function?
   The drawing function is implemented by using InkPresenter.
   1. When mouseleftbuttondown, create new Stroke as currentstroke, add to InkPresenter.
   2. While mousemoving, if currentstroke is not null, add current position as new StylusPoints
      to currentstroke.
   3. When mouseleftbuttondown, set currentstroke to null.
   
   For creating more complex drawing function with inkprsenter, you could check  
   http://msdn.microsoft.com/en-us/magazine/cc721604.aspx

References:


Communication Between Local Silverlight-Based Applications
http://msdn.microsoft.com/en-us/library/dd833063(VS.95).aspx