How to handle dependency injection in a WPF/MVVM application

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I have been using Ninject, and found that it’s a pleasure to work with. Everything is set up in code, the syntax is fairly straightforward and it has a good documentation (and plenty of answers on SO).

So basically it goes like this:

Create the view model, and take the IStorage interface as constructor parameter:

class UserControlViewModel
{
    public UserControlViewModel(IStorage storage)
    {

    }
}

Create a ViewModelLocator with a get property for the view model, which loads the view model from Ninject:

class ViewModelLocator
{
    public UserControlViewModel UserControlViewModel
    {
        get { return IocKernel.Get<UserControlViewModel>();} // Loading UserControlViewModel will automatically load the binding for IStorage
    }
}

Make the ViewModelLocator an application wide resource in App.xaml:

<Application ...>
    <Application.Resources>
        <local:ViewModelLocator x:Key="ViewModelLocator"/>
    </Application.Resources>
</Application>

Bind the DataContext of the UserControl to the corresponding property in the ViewModelLocator.

<UserControl ...
             DataContext="{Binding UserControlViewModel, Source={StaticResource ViewModelLocator}}">
    <Grid>
    </Grid>
</UserControl>

Create a class inheriting NinjectModule, which will set up the necessary bindings (IStorage and the viewmodel):

class IocConfiguration : NinjectModule
{
    public override void Load()
    {
        Bind<IStorage>().To<Storage>().InSingletonScope(); // Reuse same storage every time

        Bind<UserControlViewModel>().ToSelf().InTransientScope(); // Create new instance every time
    }
}

Initialize the IoC kernel on application startup with the necessary Ninject modules (the one above for now):

public partial class App : Application
{       
    protected override void OnStartup(StartupEventArgs e)
    {
        IocKernel.Initialize(new IocConfiguration());

        base.OnStartup(e);
    }
}

I have used a static IocKernel class to hold the application wide instance of the IoC kernel, so I can easily access it when needed:

public static class IocKernel
{
    private static StandardKernel _kernel;

    public static T Get<T>()
    {
        return _kernel.Get<T>();
    }

    public static void Initialize(params INinjectModule[] modules)
    {
        if (_kernel == null)
        {
            _kernel = new StandardKernel(modules);
        }
    }
}

This solution does make use of a static ServiceLocator (the IocKernel), which is generally regarded as an anti-pattern, because it hides the class’ dependencies. However it is very difficult to avoid some sort of manual service lookup for UI classes, since they must have a parameterless constructor, and you cannot control the instantiation anyway, so you cannot inject the VM. At least this way allows you to test the VM in isolation, which is where all the business logic is.

If anyone has a better way, please do share.

EDIT:
Lucky Likey provided an answer to get rid of the static service locator, by letting Ninject instantiate UI classes. The details of the answer can be seen here

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