I want to start silverlight development inside an application which developed by WPF.
Actually we want to add silverlight featuretoan existing WPF project. what should we consider and how todo this
I saw Getting started with Silverlight development and it was not my answer
I mark this as a Community Wiki.
Please clarify your intent. What do you mean by a Silverlight feature ?
Silverlight is a subset of WPF, but is intended for a Web application (i.e. running inside a Web browser, using the .NET framework provided by the browser plug-in), while WPF is meant for a desktop application (i.e. running outside of a browser, using the full .NET present on the disk).
(there is the notion of running WPF inside the browser, but that is still using the full .NET framework).
"Adding" Silverlight to WPF doesn't make much sense because you can accomplish whatever you need to do in regular WPF for the most part. If you already have a WPF application you are enforcing windows and the full .NET client run time so you are going to get any deployment benefits.
I assume what you may be considering (since you mentioned XBAP) is to re-write or recompile your current WPF XBAP application into a Silverlight application? This way you get cross platform web deployment with the full Client run time requirement.
If this is the case then you would not be "adding" to your existing solution. It would be more an exercise in porting the existing application over to Silverlight. With SL3 this is less painful then before (and if SL 4 is an option it will be an even better experience).
My first step would be to simply create a new Silverlight application and begin moving your code over and seeing how far you get.