what are the necessary steps to be keep in mind, if anybody wants to convert Normal WPF project to MVVM enabled one?

If anybody wants to convert a Normal WPF project to MVVM enabled one, what are the main points to be keep in mind while restructuring the entire application开发者_开发问答. What are the main hurdles to accomplish the task?

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Go through:

http://msdn.microsoft.com/en-us/magazine/dd419663.aspxlink text

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Separate all presentation logic in view model, buisness logic in model, keep view without codebehind(sometimes not possible) ?