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    <p>Mick N's pointer helped, but what really got me over the hump was this post by Jeremy Likness: <a href="http://csharperimage.jeremylikness.com/2010/04/model-view-viewmodel-mvvm-explained.html" rel="nofollow noreferrer">http://csharperimage.jeremylikness.com/2010/04/model-view-viewmodel-mvvm-explained.html</a></p> <p>Here's the sample for the benefit of others (assuming I'm not doing anything really stupid):</p> <p>First, I started using the Mvvm-Light Windows Phone 7 project.</p> <p>I added a checkbox to my MainPage.xaml: <code></p> <pre><code> &lt;CheckBox Content="Switch 1" IsChecked="{Binding Switch1.PowerState, Mode=TwoWay}" Height="72" HorizontalAlignment="Left" Margin="24,233,0,0" Name="checkBox1" VerticalAlignment="Top" Width="428" /&gt; </code></pre> <p></code></p> <p>Notice the IsChecked is bound to Switch1.PowerState using the TwoWay mode so that the property flows both ways.</p> <p>A key learning for me is how to enable communication from my timer callback (TimerCB) which will be running on a new thread to the Silverlight UI thread. I used the Mvvm-Light DispatcherHelper.CheckBeginInvokeOnUI helper which waits on the UI thread.</p> <p>I then had to decide whether to implement INotifyPropertyChanged myself in my model, or use Mvvm-Light's ViewModelBase implementation. I actually tried it both ways and had it working but decided I liked using ViewModelBase better because it supports "broadcast" and I think in my actual project that will be handy because I will have multiple ViewModels. It seems a bit uncouth to be basing a "Model" on ViewModelBase class, but I don't think there's any harm in doing so. (???). </p> <p>My model .cs is below.<br> <code></p> <pre><code>public class OnOffSwitchClass : ViewModelBase // ignore that it's derived from ViewModelBase! { private const Int32 TIMER_INTERVAL = 5000; // 5 seconds private Timer _timer; // Upon creation create a timer that changes the value every 5 seconds public OnOffSwitchClass() { _timer = new System.Threading.Timer(TimerCB, this, TIMER_INTERVAL, TIMER_INTERVAL); } private static void TimerCB(object state) { // Alternate between on and off ((OnOffSwitchClass)state).PowerState = !((OnOffSwitchClass)state).PowerState; } public const string PowerStatePropertyName = "PowerState"; private bool _myProperty = false; public bool PowerState { get { return _myProperty; } set { if (_myProperty == value) { return; } var oldValue = _myProperty; _myProperty = value; // Update bindings and broadcast change using GalaSoft.MvvmLight.Messenging GalaSoft.MvvmLight.Threading.DispatcherHelper.CheckBeginInvokeOnUI(() =&gt; RaisePropertyChanged(PowerStatePropertyName, oldValue, value, true)); } } } </code></pre> <p></code></p> <p>The MainViewModel.cs was modified to include the following</p> <p><code> private OnOffSwitchClass _Switch1 = new OnOffSwitchClass();</p> <pre><code>public OnOffSwitchClass Switch1 { get { return _Switch1; } } </code></pre> <p></code></p> <p>And I added a call to DispatcherHelper.Initialize(); in my App() constructor.</p> <p>Does this look right?</p>
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    1. COAs far as the Model question, in WP7 I use a model class for reading/writing to Transient memory and Isolated storage. ViewModels are for presenting data to be bound to by the Views/Pages. If you're using your Model like a view model, then maybe it should be a view model.
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    2. COI prefer calling DispatcherHelper.Initialize() in both App.xaml.cs' Appliance_Launching and Appliance_Activated methods.
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    3. COThanks Matt - why in _Launching & _Activated and not in the constructor?
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