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1. Introduction

Whatever software application you want to create, the most important problem that must be solved is the tight coupling. Mixing one layer with another is a very common mistake and it is the main reason for your application to be tightly coupled. For example: as a practical example in this article I will create a simple data entry application, which purpose is to load, create, edit, delete and save data. The most straightforward way to create the application is to put everything in the user interface (handling the button’s click events and writing the code there). It is the easiest way but it is far from the best. This will produce a low quality code and high complexity. And when the things are tightly coupled, one change can lead you into chasing breaking changes in the whole code. So the most important thing is to keep the layers separate, one layer – one responsibility. Yes, it is true, that creating an application with separate tiers requires additional work, but this may save you a headache in the future.

The most famous solutions and approaches (patterns) for creating a multi layer application are the MVC and MVP patterns. Since Silverlight does not require reinventing the wheel, these patterns and practices can be applied with great success when you create a Silverlight application. In previous articles I showed you how the Model-View-Presenter (MVP) pattern and the Model-View-Controller (MVC) pattern can be used in Silverlight. Today I decided to continue and to present you another pattern – it is the Model-View-ViewModel (MVVM). MVVM is tailor-made for WPF and it is an adaptation of the MVC and MVP.

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