How can I access and fire Events from a MediaElement from a View in a ViewModel?

Question

I'm creating a Windows 10 app and I am implementing speech functionality. The user needs to be able to listen to the whole speech, respond with voice, and then receive a response back. But, I'm having troubles making this purely MVVM.

Okay, for MediaElement.Ended, I can just use a behavior, right? Set the Ended behavior to my own command which fires the method I want?

As for setting the source to synthesized text and setting AutoPlay to true, I can just bind those to properties in my ViewModel.

But, MediaElement.Play()...How do I fire this method from a ViewModel if I can't access the MediaElement?

I understand I can do some "hacks" to make it work or use the code-behind, but my aim is to do this "purely MVVM", where my ViewModel knows nothing of the view and any view elements.

Thanks anyone for the help.

Answer 1

You could do something like this:

MVVM Project:

-ServiceLocator.cs

public class ServiceLocator
{
    public static ServiceLocator Instance = new ServiceLocator();

    private ServiceLocator()
    {
    }

    private readonly IDictionary<Type, Type> TypeMap = new Dictionary<Type, Type>();

    private readonly IDictionary<Type, object> TypeMapInstances = new Dictionary<Type, object>();

    public void Register<TInterface, TClass>()
    {
        TypeMap.Add(typeof(TInterface), typeof(TClass));
    }

    public void Register<TClass>(object instance)
    {
        TypeMapInstances.Add(typeof(TClass), instance);
    }

    public T GetService<T>()
    {
        Type type = typeof(T);
        object resolvedType = null;

        try
        {
            if (TypeMapInstances.ContainsKey(type))
            {
                resolvedType = TypeMapInstances[type];
            }
            else
            {
                resolvedType = Activator.CreateInstance(TypeMap[type]);
                TypeMapInstances.Add(type, resolvedType);
            }
        }
        catch (Exception)
        {
            return default(T);
            //throw new Exception(string.Format("Could not resolve type {0}", type.FullName));
        }

        return (T)resolvedType;
    }
}

-IMediaElementService.cs

public interface IMediaElementService
{
    void Play();
}

-YourVMClass.cs

public void Foo()
{
    var mediaElementService = ServiceLocator.Instance.GetService<IMediaElementService>();
    mediaElementService.Play();
}

Client Project:

-MediaElementService.cs

public class MediaElementService : IMediaElementService
{
    public void Play()
    {
        App.MediaElement.Play();
    }
}

-App.cs

public static MediaElement MediaElement;

private void OnLaunched(LaunchActivatedEventArgs e)
{
    ServiceLocator.Instance.Register<IMediaElementService, MediaElementService>();
}

-YourView.xaml

<MediaElement x:Name="_mediaElement" />

-YourView.xaml.cs

public YourView(){
    InitializeComponent();
    App.MediaElement = _mediaElement;
}

And that's all, although this is only one of several ways that could achieve the same.