Getting Started: MvvmCross with Xamarin Forms (Part 2)

Again, remove the inheritance specified in MainPage.xaml.cs

public partial class MainPage
{
     public MainPage()
     {
         InitializeComponent();
     }
}

The next step involves adding a Setup class to each of the head projects, and then creating an instance of the Setup class to invoke MvvmCross when the application starts up.

UWP

The UWP Setup inherits from MvxFormsWindowsSetup and unlike the Android and iOS Setup classes, the UWP Setup needs to override the default log behaviour by setting the log provider type to None and then creating an instance of the EmptyVoidLogProvider  (the implementation of this is coming up soon) – this should be fixed in a future MvvmCross version.

public class Setup : MvxFormsWindowsSetup
{
     public Setup(Frame rootFrame, LaunchActivatedEventArgs e) : base(rootFrame, e)
     {
     }

    protected override MvxLogProviderType GetDefaultLogProviderType() => MvxLogProviderType.None;

    protected override IMvxLogProvider CreateLogProvider() => new EmptyVoidLogProvider();

    protected override IEnumerable<Assembly> GetViewAssemblies()
     {
         return new List<Assembly>(base.GetViewAssemblies().Union(new[] { typeof(MvvmcrossGettingStarted.App).GetTypeInfo().Assembly }));
     }

    protected override MvxFormsApplication CreateFormsApplication() => new MvvmcrossGettingStarted.App();

    protected override IMvxApplication CreateApp() => new Core.GettingStartedApplication();
}

Now in App.xaml.cs we need to replace

Xamarin.Forms.Forms.Init(e);

with

var setup = new Setup(rootFrame, e);
setup.Initialize();

And in Main.xaml.cs replace

LoadApplication(new MvvmcrossGettingStarted.App());

with

var start = Mvx.Resolve<IMvxAppStart>();
start.Start();

var presenter = Mvx.Resolve<IMvxFormsViewPresenter>() as MvxFormsUwpViewPresenter;
LoadApplication(presenter.FormsApplication);

Finally, we need to add the EmptyVoidLogProvider

public class EmptyVoidLogProvider : IMvxLogProvider
{
     private readonly EmptyVoidLog voidLog;

    public EmptyVoidLogProvider()
     {
         voidLog = new EmptyVoidLog();
     }

    public IMvxLog GetLogFor<T>()
     {
         return voidLog;
     }

    public IMvxLog GetLogFor(string name)
     {
         return voidLog;
     }

    public IDisposable OpenNestedContext(string message)
     {
         throw new NotImplementedException();
     }

    public IDisposable OpenMappedContext(string key, string value)
     {
         throw new NotImplementedException();
     }

    public class EmptyVoidLog : IMvxLog
     {
         public bool Log(MvxLogLevel logLevel, Func<string> messageFunc, Exception exception = null, params object[] formatParameters)
         {
             return true;
         }
     }
}

Now when we build and run the UWP project we can see that the MainPage is shown and is data bound to the MainViewModel.

iOS

The iOS Setup is the simplest out of the three platforms.

public class Setup : MvxFormsIosSetup
{
     public Setup(IMvxApplicationDelegate applicationDelegate, UIWindow window)
         : base(applicationDelegate, window)
     {
     }

    protected override IEnumerable<Assembly> GetViewAssemblies()
     {
         return new List<Assembly>(base.GetViewAssemblies().Union(new[] { typeof(MvvmcrossGettingStarted.App).GetTypeInfo().Assembly }));
     }

    protected override MvxFormsApplication CreateFormsApplication() => new MvvmcrossGettingStarted.App();

    protected override IMvxApplication CreateApp() => new Core.GettingStartedApplication();
}

In AppDelegate we need to change the inheritance from  global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate to MvxFormsApplicationDelegate and change the FinishedLaunching method as follows:

public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
     Window = new UIWindow(UIScreen.MainScreen.Bounds);

    var setup = new Setup(this, Window);
     setup.Initialize();

    var startup = Mvx.Resolve<IMvxAppStart>();
     startup.Start();

    LoadApplication(setup.FormsApplication);

    Window.MakeKeyAndVisible();

    return base.FinishedLaunching(app, options);
}

Now we’re good to build and run the iOS project

Android

Lastly, add Setup to the Android project. Note this is slightly different from the iOS and UWP projects in that the GetViewAssemblies method excludes the assembly for the Android head project. This is to avoid the MainActivity being added as a view, that based on our naming convention would match with MainViewModel giving a duplicate when attempting to resolve the View that should be rendered.

public class Setup : MvxFormsAndroidSetup
{
     public Setup(Context applicationContext) : base(applicationContext)
     {
     }

    protected override IEnumerable<Assembly> GetViewAssemblies()
     {
         return new List<Assembly>(base.GetViewAssemblies()
             .Union(new[] { typeof(MvvmcrossGettingStarted.App).GetTypeInfo().Assembly })
             .Except(new[] {this.GetType().Assembly})
             );
     }

    protected override MvxFormsApplication CreateFormsApplication() => new MvvmcrossGettingStarted.App();

    protected override IMvxApplication CreateApp() => new Core.GettingStartedApplication();
}

The MainActivity needs to be updated to change its inheritance from global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity to MvxFormsAppCompatActivity<MainViewModel>. And the OnCreate needs to be updated to

[Activity(Label = “MvvmcrossGettingStarted”, Icon = “@drawable/icon”, Theme = “@style/MainTheme”, MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : MvxFormsAppCompatActivity<MainViewModel>
//global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
     protected override void OnCreate(Bundle bundle)
     {
         TabLayoutResource = Resource.Layout.Tabbar;
         ToolbarResource = Resource.Layout.Toolbar;

        base.OnCreate(bundle);

        var startup = Mvx.Resolve<IMvxAppStart>();
         startup.Start();
         InitializeForms(bundle);

     }
}

Finally the last platform, Android, is good to build and run. Note however that Android has a tendency to be a pain and that after setting everything up correctly you may still run into issues building, deploying and running. Before you waste hours looking at your code to see what you’ve done wrong, make the assumption that the tools are crap – delete both bin and obj folders from the Android head project, and uninstall the application from the device/emulator (assuming it has already been installed). Try building and running again – if this still fails, then you may indeed have something wrong with your code!