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POFat Models, skinny ViewModels and dumb Views, the best MVVM approach?
 

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    <p>Through generous help on <a href="https://stackoverflow.com/questions/851595">this question</a>, I put together the following MVVM structure which displays the changes of a model in real time in XAML (current date/time), very nice.</p> <blockquote> <p>A cool advantage of this set up is that when you look at your view <em>in design mode</em> of Visual Studio or Blend, <em>you see the time ticking by</em>, which means that <em>at design time you have access to live data from your model.</em></p> </blockquote> <p>In the process of getting this to work, I was surprised to see <strong>most of the bulk move from my ViewModel into my Model</strong>, including implementation of INotifyPropertyChange. Another change is that I <strong>no longer bind to <em>properties</em> on the ViewModel but to <em>methods</em></strong>. </p> <p>So currently this is my favorite flavor of MVVM:</p> <ol> <li><p>View is dumb: </p> <ul> <li>one ObjectDataProvider for each object you need from your model</li> <li>each ObjectDataProvider maps to a method on the ViewModel (not a property)</li> <li>no x:Name properties in XAML elements</li> </ul></li> <li><p>ViewModel is skinny:</p> <ul> <li>the only thing in your ViewModel are the <em>methods</em> to which your view binds</li> </ul></li> <li><p>Model is fat:</p> <ul> <li>the model implements INotifyPropertyChanged on each of its properties.</li> <li>for every method on your ViewModel (e.g. GetCurrentCustomer) there is a corresponding <em>singleton method</em> in your Model (e.g. GetCurrentCustomer).</li> <li>the model takes care of any real time threading functionality as in this example</li> </ul></li> </ol> <p><strong>Questions:</strong></p> <ol> <li>Those of you who have been implementing MVVM in real scenarios, is this the basic structure you have also settled upon, and if not, how does yours vary?</li> <li>How would you extend this to include routed commands and routed events?</li> </ol> <p><em>The following code will work if you just copy the XAML and code behind into a new WPF project.</em></p> <p><strong>XAML:</strong></p> <pre><code>&lt;Window x:Class="TestBinding99382.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:TestBinding99382" Title="Window1" Height="300" Width="300"&gt; &lt;Window.Resources&gt; &lt;ObjectDataProvider x:Key="DataSourceCustomer" ObjectType="{x:Type local:ShowCustomerViewModel}" MethodName="GetCurrentCustomer"/&gt; &lt;/Window.Resources&gt; &lt;DockPanel DataContext="{StaticResource DataSourceCustomer}"&gt; &lt;StackPanel DockPanel.Dock="Top" Orientation="Horizontal"&gt; &lt;TextBlock Text="{Binding Path=FirstName}"/&gt; &lt;TextBlock Text=" "/&gt; &lt;TextBlock Text="{Binding Path=LastName}"/&gt; &lt;/StackPanel&gt; &lt;StackPanel DockPanel.Dock="Top" Orientation="Horizontal"&gt; &lt;TextBlock Text="{Binding Path=TimeOfMostRecentActivity}"/&gt; &lt;/StackPanel&gt; &lt;/DockPanel&gt; &lt;/Window&gt; </code></pre> <p><strong>Code Behind:</strong></p> <pre><code>using System.Windows; using System.ComponentModel; using System; using System.Threading; namespace TestBinding99382 { public partial class Window1 : Window { public Window1() { InitializeComponent(); } } //view model public class ShowCustomerViewModel { public Customer GetCurrentCustomer() { return Customer.GetCurrentCustomer(); } } //model public class Customer : INotifyPropertyChanged { private string _firstName; private string _lastName; private DateTime _timeOfMostRecentActivity; private static Customer _currentCustomer; private Timer _timer; public string FirstName { get { return _firstName; } set { _firstName = value; this.RaisePropertyChanged("FirstName"); } } public string LastName { get { return _lastName; } set { _lastName = value; this.RaisePropertyChanged("LastName"); } } public DateTime TimeOfMostRecentActivity { get { return _timeOfMostRecentActivity; } set { _timeOfMostRecentActivity = value; this.RaisePropertyChanged("TimeOfMostRecentActivity"); } } public Customer() { _timer = new Timer(UpdateDateTime, null, 0, 1000); } private void UpdateDateTime(object state) { TimeOfMostRecentActivity = DateTime.Now; } public static Customer GetCurrentCustomer() { if (_currentCustomer == null) { _currentCustomer = new Customer { FirstName = "Jim" , LastName = "Smith" , TimeOfMostRecentActivity = DateTime.Now }; } return _currentCustomer; } //INotifyPropertyChanged implementation public event PropertyChangedEventHandler PropertyChanged; private void RaisePropertyChanged(string property) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(property)); } } } } </code></pre>
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    1. CORegarding RelayCommands and RoutedCommands, you might want to have a look at these answers: http://stackoverflow.com/questions/650010/mvvm-routed-and-relay-command/6441472#6441472
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