MVVM Light for Xamarin Forms and WPF - wpf

Question

I'm trying to make an cross-plattform app, that will work for Xamarin.Forms and WPF (like this: https://github.com/C0D3Name/XamFormsWpf) in combination with MVVM light.
MVVM Light is quite new to me and i didn't find a clear tutorial for what i want to do. On Xamarin.Forms the DependencyInjection is done by
SQLiteConnection database = DependencyService.Get<ISQLite>().GetConnection("db.sqlite");
How is this done in MVVM light? Do i have to pass the different plattform-implementations of ISQLite in as parameter?
I already created the ViewModelLocator in my PCL:
public class ViewModelLocator
{
/// <summary>
/// Register all the used ViewModels, Services et. al. witht the IoC Container
/// </summary>
public ViewModelLocator()
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
SimpleIoc.Default.Register<MainViewModel>();
// My DataService is using the connection from ISQlite
SimpleIoc.Default.Register<IDataService, DataService>();
}
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance",
"CA1822:MarkMembersAsStatic",
Justification = "This non-static member is needed for data binding purposes.")]
public MainViewModel Main
{
get
{
return ServiceLocator.Current.GetInstance<MainViewModel>();
}
}
}
public interface ISQLite
{
SQLiteConnection GetConnection(string sqliteFilename);
}
As far as i understood the SimpleIoc, i have to register the interface to a concrete implementation, but how does my DataService know about the correct ISQLite Implementation?
I hope my question is understandable.

Answer 1

From official docs:
SimpleIoc - A very simple IOC container with basic functionality needed to register and resolve instances.
DependencyService - Xamarin.Forms allows developers to define behavior in platform-specific projects. DependencyService then finds the right platform implementation, allowing shared code to access the native functionality.
So you would want to use SimpleIoc to create your PCL dependency injection graph (IDataService for example)
And you will have to use DependencyService to provide platform specific functionality. One example for DependencyService use would be loading a html file located on the device into webview. Since the locations of assets on iOS and Android are different you will have add platform specific implementation for base url and then use DependencyService in your pcl. Another example would be IO.
So in your case if you need platform specific implementations of ISQlite you will have to use DependencyService. If not you may want (or not) to use SimpleIoc to add concrete implementation of ISQlite interface to your dependency graph.
Hope that helps.
Also have a look at Akavache. We use it with a great success in Xamarin.Forms projects.

Answer 2

Finally i found a working solution. The (async) Sqlite-Connection is used as parameter for my ViewModelLocator
public class App : Application
{
private static ViewModelLocator locator;
public static ViewModelLocator Locator
{
get
{
if (locator == null)
{
var connection = DependencyService.Get<ISQLite>().GetConnection("db.sqlite");
locator = new ViewModelLocator(connection);
}
return locator;
}
}
}
...and the locator injects the connection into the DataService constructor:
public class ViewModelLocator
{
public ViewModelLocator(SQLiteConnectionWithLock connection)
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
SimpleIoc.Default.Register<IDataService>(() => new DataService(connection));
// ViewModels
SimpleIoc.Default.Register<MainViewModel>();
}
public MainViewModel Main => ServiceLocator.Current.GetInstance<MainViewModel>();
}