Well when you are developing on the Windows Phone and are trying to use MVVM, you'll notice not everything is 'real' MVVMable
You'll notice it mostly when you are using controls that don't have much bindable items... so sometimes you'll loose control of the View - ViewModel link.
An example I came across, where I was stuck with using the normal MVVM way, was when I added some pushpins on a Bing Maps control and wanted to adjust the view of the Bing Maps so that it would show all pushpins just added!
There is a real nice method on the Bing Maps called SetView()! It accepts a LocationRect as parameter and you can create such a LocationRect from a IEnumerable list of Geocoördinates. In other words if you have the PushPin collection, you can pass this along and the Bing Map will zoom and center to an appropriate size / place to show all pushpins in the given collection.
But the bad part, the SetView is a method and there is no bindable property on the map to use to control this. So you are a bit stuck when you only want to use the MVVM pattern.
So how to solve this, well it's actually very easy
When you are using the MVVMLight Toolkit from Laurent Bugnion, you can use the Messaging feature for this!
So what do you need to do.
First create a class inside the Model folder ( or in the root of the project ) called PushPinModel and add a List<Geocoordinate> GeoCoordinateList property inside of it.
Then assuming you have a MainPage View, add following in the constructor of this MainPage.xaml.cs
Messenger.Default.Register<PushPinModel>(this, action => this.SetView(action));
Also add following private method inside the MainPage.xaml.cs, this method will be called each time the listener receives a message!
private void SetView(PushPinModel pushpinModel)
if (pushpinModel.GeoCoordinateList.Count > 0)
Now the only thing left to do is fill up this Geocoordinate list in the ViewModel and send out a message to the listeners!
PushPinModel pm = new PushPinModel();
pm.GeoCoordinateList.Add(new GeoCoordinate(51.10524, 4.54229));
pm.GeoCoordinateList.Add(new GeoCoordinate(51.3411, 3.2398));