Question

Caliburn.Micro 3.0（和Caliburn.Micro.Xamarin.Forms）是否实现了在Xamarin.Forms中模仿/支持Navigation.PushModalAsync的功能？

Answer 1

没有。它不是内置的，但它很容易增强它。通常，MvvM框架由ViewModels导航。 Caliburn遵循这种模式。所以它需要某种导航服务。该导航服务负责为ViewModel创建视图，并调用视图框架（在我们的例子中为Xamarin.Froms）特定的导航功能。 NavigationPageAdapter是我们正在寻找的东西。现在让我们加强它。

public interface IModalNavigationService : INavigationService
{
    Task NavigateModalToViewModelAsync<TViewModel>(object parameter = null, bool animated = true);
    // TODO: add more functions for closing
}

public class ModalNavigationPageAdapter : NavigationPageAdapter, IModalNavigationService
{
    private readonly NavigationPage _navigationPage;

    public ModalNavigationPageAdapter(NavigationPage navigationPage) : base(navigationPage)
    {
        _navigationPage = navigationPage;
    }

    public async Task NavigateModalToViewModelAsync<TViewModel>(object parameter = null, bool animated = true)
    {
        var view = ViewLocator.LocateForModelType(typeof(TViewModel), null, null);

        await PushModalAsync(view, parameter, animated);
    }

    private Task PushModalAsync(Element view, object parameter, bool animated)
    {
        var page = view as Page;

        if (page == null)
            throw new NotSupportedException(String.Format("{0} does not inherit from {1}.", view.GetType(), typeof(Page)));

        var viewModel = ViewModelLocator.LocateForView(view);

        if (viewModel != null)
        {
            TryInjectParameters(viewModel, parameter);

            ViewModelBinder.Bind(viewModel, view, null);
        }

        page.Appearing += (s, e) => ActivateView(page);
        page.Disappearing += (s, e) => DeactivateView(page);

        return _navigationPage.Navigation.PushModalAsync(page, animated);
    }

    private static void DeactivateView(BindableObject view)
    {
        if (view == null)
            return;

        var deactivate = view.BindingContext as IDeactivate;

        if (deactivate != null)
        {
            deactivate.Deactivate(false);
        }
    }

    private static void ActivateView(BindableObject view)
    {
        if (view == null)
            return;

        var activator = view.BindingContext as IActivate;

        if (activator != null)
        {
            activator.Activate();
        }
    }
}

我们刚刚声明了扩展IModalNavigationService的接口INavigationService并在ModalNavigationPageAdapter中实现了它。不幸的是，Caliburn将很多函数私有化，因此我们必须将它们复制到我们继承的版本中。

在校准中，您可以通过navigationservice.For<VM>().Navigate()进行导航。我们想要遵循这种风格，因此我们必须实现像navigationservice.ModalFor<VM>().Navigate()这样的扩展方法。

public static class ModalNavigationExtensions
{
    public static ModalNavigateHelper<TViewModel> ModalFor<TViewModel>(this IModalNavigationService navigationService)
    {
        return new ModalNavigateHelper<TViewModel>().AttachTo(navigationService);
    }
}

此方法返回ModalNavigateHelper，简化了导航服务的使用（类似于Caliburn的NavigateHelper）。它几乎是一个副本，但对于IModalNavigationService。

public class ModalNavigateHelper<TViewModel>
{
    readonly Dictionary<string, object> parameters = new Dictionary<string, object>();
    IModalNavigationService navigationService;

    public ModalNavigateHelper<TViewModel> WithParam<TValue>(Expression<Func<TViewModel, TValue>> property, TValue value)
    {
        if (value is ValueType || !ReferenceEquals(null, value))
        {
            parameters[property.GetMemberInfo().Name] = value;
        }

        return this;
    }

    public ModalNavigateHelper<TViewModel> AttachTo(IModalNavigationService navigationService)
    {
        this.navigationService = navigationService;

        return this;
    }

    public void Navigate(bool animated = true)
    {
        if (navigationService == null)
        {
            throw new InvalidOperationException("Cannot navigate without attaching an INavigationService. Call AttachTo first.");
        }

        navigationService.NavigateModalToViewModelAsync<TViewModel>(parameters, animated);
    }
}

最后但并非最不重要的是，我们必须使用我们闪亮的新导航服务而不是旧的导航服务。 App班级正在NavigationPageAdapter中将INavigationService PrepareViewFirst注册为public class App : FormsApplication { private readonly SimpleContainer container; public App(SimpleContainer container) { this.container = container; container .PerRequest<LoginViewModel>() .PerRequest<FeaturesViewModel>(); Initialize(); DisplayRootView<LoginView>(); } protected override void PrepareViewFirst(NavigationPage navigationPage) { var navigationService = new ModalNavigationPageAdapter(navigationPage); container.Instance<INavigationService>(navigationService); container.Instance<IModalNavigationService>(navigationService); } }中的单身人士。我们必须按如下方式进行更改

INavigationService

我们正在为IModalNavigationService和PopModalAsync注册我们的导航服务。

正如您在评论中看到的那样，您必须实现自己调用public static Hashmap<String, Clans> playersClan = new Hashmap<>();的关闭函数。

Caliburn.Micro 3.0相当于Xamarin.Forms Navigation.PushModalAsync

1 个答案: