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POWhere to store application settings/state in a MVVM application
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copied!<p>I'm experimenting with MVVM for the first time and really like the separation of responsibilities. Of course any design pattern only solves many problems - not all. So I'm trying to figure out where to store application state and where to store application wide commands. </p> <p>Lets say my application connects to a specific URL. I have a ConnectionWindow and a ConnectionViewModel that support gathering this information from the user and invoking commands to connect to the address. The next time the application starts, I want to reconnect to this same address without prompting the user. </p> <p>My solution so far is to create an ApplicationViewModel that provides a command to connect to a specific address and to save that address to some persistent storage (where it's actually saved is irrelevant for this question). Below is an abbreviated class model.</p> <p>The application view model:</p> <pre><code>public class ApplicationViewModel : INotifyPropertyChanged { public Uri Address{ get; set; } public void ConnectTo( Uri address ) { // Connect to the address // Save the addres in persistent storage for later re-use Address = address; } ... } </code></pre> <p>The connection view model:</p> <pre><code>public class ConnectionViewModel : INotifyPropertyChanged { private ApplicationViewModel _appModel; public ConnectionViewModel( ApplicationViewModel model ) { _appModel = model; } public ICommand ConnectCmd { get { if( _connectCmd == null ) { _connectCmd = new LambdaCommand( p => _appModel.ConnectTo( Address ), p => Address != null ); } return _connectCmd; } } public Uri Address{ get; set; } ... } </code></pre> <p>So the question is this: Is an ApplicationViewModel the right way to handle this? How else might you store application state?</p> <p><strong>EDIT:</strong> I'd like to know also how this affects testability. One of the primary reasons for using MVVM is the ability to test the models without a host application. Specifically I'm interested in insight on how centralized app settings affect testability and the ability to mock out the dependent models.</p>

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