Xamarin.Forms + Prism で NavigationPage を使う

Xamarin.Forms の NavigationPage を、 Prism で良い感じに使ってみます。

NavigationPage ってなんぞや？というのはこれをみてね。

基本的な構造は、下の記事を参考にしました。

ただ、 Prism のメジャーバージョンの違いでいろいろ変わっていますが、
だいたい同じ感じでいけます。

NavigationService.cs

public class NavigationService : INavigationService
{
    public static NavigationPage RootPage { get; private set; }

    /// <summary>
    /// Navigates to the most recent entry in the back navigation history by popping the calling Page off the navigation stack.
    /// </summary>
    /// <param name="useModalNavigation">If <c>true</c> uses PopModalAsync, if <c>false</c> uses PopAsync</param>
    /// <param name="animated">If <c>true</c> the transition is animated, if <c>false</c> there is no animation on transition.</param>
    public void GoBack(bool useModalNavigation = true, bool animated = true)
    {
        RootPage.PopAsync();
        PrepareNavigation(RootPage.CurrentPage, null);
    }

    /// <summary>
    /// Initiates navigation to the target specified by the <typeparamref name="T" />.
    /// </summary>
    /// <typeparam name="T">The type which will be used to identify the name of the navigation target.</typeparam>
    /// <param name="parameters">The navigation parameters</param>
    /// <param name="useModalNavigation">If <c>true</c> uses PopModalAsync, if <c>false</c> uses PopAsync</param>
    /// <param name="animated">If <c>true</c> the transition is animated, if <c>false</c> there is no animation on transition.</param>
    public void Navigate<T>(NavigationParameters parameters = null, bool useModalNavigation = true, bool animated = true)
    {
        var page = Activator.CreateInstance(typeof (T)) as Page;
        if (page == null)
            throw new InvalidCastException("T cannot cast to Xamarin.Forms.Page.");
        RootPage.PushAsync(page, animated);
        PrepareNavigation(page, parameters);
    }

    /// <summary>
    /// Initiates navigation to the target specified by the <paramref name="name" />.
    /// </summary>
    /// <param name="name">The name of the target to navigate to.</param>
    /// <param name="parameters">The navigation parameters</param>
    /// <param name="useModalNavigation">If <c>true</c> uses PopModalAsync, if <c>false</c> uses PopAsync</param>
    /// <param name="animated">If <c>true</c> the transition is animated, if <c>false</c> there is no animation on transition.</param>
    public void Navigate(string name, NavigationParameters parameters = null, bool useModalNavigation = true, bool animated = true)
    {
        var type = Type.GetType(name);
        var page = Activator.CreateInstance(type) as Page;
        if (page == null)
            throw new InvalidCastException("T cannot cast to Xamarin.Forms.Page.");
        RootPage.PushAsync(page, animated);
        PrepareNavigation(page, parameters);
    }

    public void GoHome(bool animated = true)
    {
        RootPage.PopToRootAsync(animated);
        PrepareNavigation(RootPage.CurrentPage, null);
    }

    public static void Configure(NavigationPage rootPage)
    {
        RootPage = rootPage;
    }

    private static void PrepareNavigation(Page page, NavigationParameters parameters)
    {
        var navigationAware = page.BindingContext as INavigationAware;
        navigationAware?.OnNavigatedTo(parameters);

        EventHandler onDisappearing = null;
        onDisappearing = (sender, e) =>
        {
            page.Disappearing -= onDisappearing;
            navigationAware?.OnNavigatedFrom(null);
        };
        page.Disappearing += onDisappearing;
    }
}

ViewModel の状態復元などは未実装です。そのうちします。

次は App クラス。
Xamarin.iOS や Xamarin.Android の LoadApplication とかで呼び出されるクラスです。

public class App : Application
{
    public App()
    {
        var bs = new Bootstrapper();
        bs.Run(this);
    }
}

とりあえず、必要最低限としてこんな感じでいいんじゃないかなと。

そして、 Bootstrapper

public class Bootstrapper : UnityBootstrapper
{
    /// <summary>
    /// Creates the root <see cref="T:Xamarin.Forms.Page" /> for the application.
    /// </summary>
    /// <returns>
    /// The <see cref="T:Xamarin.Forms.Page" />
    /// </returns>
    protected override Page CreateMainPage()
    {
        return NavigationService.RootPage;
    }

    /// <summary>
    /// Used to register types with the container that will be used by your application.
    /// </summary>
    protected override void RegisterTypes()
    {
        Container.RegisterType<INavigationService, NavigationService>(new ContainerControlledLifetimeManager());
        NavigationService.Configure(new RootPage());
    }

    /// <summary>
    /// Configures the <see cref="T:Prism.Mvvm.ViewModelLocator" /> used by Prism.
    /// </summary>
    protected override void ConfigureViewModelLocator()
    {
        ViewModelLocationProvider.SetDefaultViewModelFactory(type => Container.Resolve(type));
    }
}