MVVM Dependency Injection with Service Locator

Kevin Marois

I want to automatically bind Views to ViewModels that consume services. For example, my sample app uses an RSS Service to get RSS feeds. In production I want the concrete service. If I want to run Unit Tests on it, I want to pass in a mock service.

public MainWindowViewModel(IRssService rssService)
{
_rssService = rssService;
}

First, I created a Service Locator class. This class works fine:

public class ServiceLocator : IServiceLocator
{
private IDictionary<object, object> _services;

public ServiceLocator(bool isTestMode)
{
	\_services = new Dictionary<object, object>();

	if (isTestMode)
	{
		// Add mock services to the dictionary
		this.\_services.Add(typeof(IRssService), new FakeRssService());
	}
	else
	{
		// Add Runtime services to the dictionary
		this.\_services.Add(typeof(IRssService), new RssService());
	}
}

public T Get<T>()
{
	try
	{
		return (T)\_services\[typeof(T)\];
	}
	catch (KeyNotFoundException)
	{
		throw new ApplicationException("The requested service is not registered");
	}
}

}

Next, I created a ViewModelLocator class

public class ViewModelLocator
{
// List of ViewModels
private List<object> _viewModels;

// Service Locator
private IServiceLocator \_serviceLocator;

public bool IsTestMode { get; set; }

// Main Window View Model
public MainWindowViewModel MainWindowVM 
{
    get { return Get<MainWindowViewModel>(); }
}

//CTOR
internal ViewModelLocator()
{
	\_serviceLocator = new ServiceLocator(IsTestMode);

	\_viewModels = new List<object>();

	\_viewModels.Add(new MainWindowViewModel(\_serviceLocator.Get<IRssService>()));
}

// Get to retrieve the VM
public T Get<T>()
{
    try
    {
        var vm = (T)\_viewModels.FirstOrDefault(x => x is T);
        return vm;
        //return (T)\_viewModels\[typeof(T)\];
    }
    catch (KeyNotFoundException)
    {
        throw new ApplicationException("The requested service is not registered");
    }
}

}

Next I wired it all up XAML - App

<Applic