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    <p>Some design patterns to consider are <a href="http://en.wikipedia.org/wiki/Inversion_of_control" rel="nofollow">Inversion of Control (IoC)</a> and <a href="http://martinfowler.com/eaaDev/EventAggregator.html" rel="nofollow">Event Aggregator</a>.</p> <p>For C# / MVVM, the <a href="http://caliburnmicro.codeplex.com/" rel="nofollow">Caliburn Micro Framework</a> (is one of a couple that) makes IoC and Event Aggregator much easier.</p> <p>You correctly identified a core concern of MVVM in that there is no off-the-shelf solution to truely decouple the ViewModel from the View. It is a core concept that ViewModels are purpose built to be pared with Views. The issue comes down to how to manage instances of ViewModel / View pairings.</p> <p>View first approach assumes that the View knows about and can instantiate ViewModels as needed - this is a problem for SoC because any View class now has multiple responsibilities; spinning up a ViewModel, and handling UI.</p> <p>View Model first is difficult because it often leads to breaking one of the main tennants of MVVM - that the VM should be testable without any associated views.</p> <p>This is where IoC comes in, typically. The IoC typically resides in the View layer (this is to allow it to have access to all View and ViewModel classes as needed) it need not be a View itself. It's often better to think of your IoC manager as a Controller - which kind of leads to a pseudo pattern of MVCVM. The sole purpose of this "controler" becomes providing View and ViewModel instance pairings to whoever needs it.</p> <p>Event Aggregator pattern really helps with this because classes in the ViewModel and View no longer need to worry about who they are paired with, and can interract only with other classes in their own level. A particular View Model need not care who sent the event "Update Load Progress" all it needs to be responsible for processing the results of the event by setting it's progress property.</p>
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    1. PODriving a MVVM application
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    1. COYes, Caliburn introduces a whole new way of how to handle such scenarios and brings in some support for other problems like EventToCommand (do not know the exact name in Caliburn). IoC is always an issue, even in simple applications.
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    2. COThe Prism Eventaggregator looks very interesting, perhaps this is what any "controller" / "presenter" / "messanger" should have.
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    3. CO@MareInfinitus I never used PRISM, but I hear it also has a good framework for Egent Aggregator and IoC patterns. Once I started using Event Aggregator pattern, I never looked back...
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