WPF Twitter client with Model-View-ViewModel Design Pattern step by step

IntroductionThis article details real world example of how to use a Model-View-ViewModel Design Pattern. I split the process of development into steps. Each step is based on the previous one and adds some specific functionality. At the end of each step we will have a working application. As the example I chose Twitter Client. I suppose it is comprehensible and useful. I’ll use TweetSharp library