MVVM Light IoC not Binding? What am I missing? - windows-phone-7

Question

I have a windows 7 phone application that I am working on. I made a couple service classes with interfaces but every-time I try to navigate too these views they now crash.
I setup my project to load one of these views as soon as the emulator loads up(through WMAppManifest.xml)
I have something like this
public interface IGpsService
{
void StartGps();
GeoPosition<GeoCoordinate> CurrentPostion();
}
public class GpsService : IGpsService
{
private GeoCoordinateWatcher gpsWatcher;
public GpsService()
{
gpsWatcher = new GeoCoordinateWatcher(GeoPositionAccuracy.Default)
{
MovementThreshold = 20,
};
}
public void StartGps()
{
gpsWatcher.Start();
}
public GeoPosition<GeoCoordinate> CurrentPostion()
{
return gpsWatcher.Position;
}
}
my view model locator
static ViewModelLocator()
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
if (ViewModelBase.IsInDesignModeStatic)
{
SimpleIoc.Default.Register<IGpsService, Design.GpsDataService>();
}
else
{
SimpleIoc.Default.Register<IGpsService, GpsService>();
}
SimpleIoc.Default.Register<AddProductPriceVm>();
}
// AddProductPrice.xaml.cs
public AddProductPrice(IGpsService gpsService)
{
InitializeComponent();
}
Does the Ioc only bind to View Models or something? Is that why it is not working as I have it in my code behind?
I am using a mix of code behind and MVVM as something are just so much easier to do with code behind.
Error Message
MissingMethodException
at System.Activator.InternalCreateInstance(Type type, Boolean nonPublic, StackCrawlMark& stackMark)
at System.Activator.CreateInstance(Type type)
at System.Windows.Navigation.PageResourceContentLoader.BeginLoad_OnUIThread(AsyncCallback userCallback, PageResourceContentLoaderAsyncResult result)
at System.Windows.Navigation.PageResourceContentLoader.<>c__DisplayClass4.<BeginLoad>b__0(Object args)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(RuntimeMethodInfo rtmi, Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean verifyAccess, StackCrawlMark& stackMark)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, StackCrawlMark& stackMark)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
at System.Delegate.DynamicInvokeOne(Object[] args)
at System.MulticastDelegate.DynamicInvokeImpl(Object[] args)
at System.Delegate.DynamicInvoke(Object[] args)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.Dispatch(DispatcherPriority priority)
at System.Windows.Threading.Dispatcher.OnInvoke(Object context)
at System.Windows.Hosting.CallbackCookie.Invoke(Object[] args)
at System.Windows.Hosting.DelegateWrapper.InternalInvoke(Object[] args)
at System.Windows.RuntimeHost.ManagedHost.InvokeDelegate(IntPtr pHandle, Int32 nParamCount, ScriptParam[] pParams, ScriptParam& pResult)
Dies in NavigationFailed
// Code to execute if a navigation fails
private void RootFrame_NavigationFailed(object sender, NavigationFailedEventArgs e)
{
if (System.Diagnostics.Debugger.IsAttached)
{
// A navigation has failed; break into the debugger
System.Diagnostics.Debugger.Break();
}
}

Answer 1

You're injecting the service directly into the View, not the viewmodel. The View is not created using SimpleIoc so has no knowledge of where to resolve your IGpsService reference in the constructor.
Your best bet, if you want to do this, is to inject the IGpsService into your viewmodel and expose it as a property. Add a DataContextChanged event to your view and, when it fires, take the IGpsService from the viewmodel.
Edit:
//AddProductPrice View
<UserControl
DataContext="{StaticResource Locator.AddProductPriceVm}">
/ AddProductPrice.xaml.cs
public AddProductPrice()
{
InitializeComponent();
DataContextChanged+=DataContextChanged
}
void DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var context=sender as AddProductPriceVm;
if(context!=null)
_myGpsService=context.GpsService;
}
//AddProductPriceVm
public class AddProductPriceVm
{
public AddProductPriceVm(IGpsService gpsService)
{
GpsService=gpsService;
}
public IGpsService GpsService{get;set;}
}
The issue isn't really a DI problem, it's just how the MVVM Light works. It expects the view to be there before it permforms and dependency injection. if you wanted to inject things directly into the view then you could look at using Prism (but it's much heavier with lots more scaffolding).