MvvmCross：混合 Xamarin.Forms 和 Android Activity 应用

Question

作为 MvvmCross 的新手，我决定创建一个小型 Xamarin.Forms 应用程序。我有一个 MainPage.xaml 绑定到它的 ViewModel MainViewModel.cs，它首先显示。我在机器人项目中有一个 FirstView.axml 及其 activity。关联的 ViewModel 与 MainViewModel 一起位于核心项目中，并命名为 FirstViewModel.cs

单击导航按钮后，我希望 MvvmCross 显示 FirstView.axml 布局并绑定到 VM。然而，

每当调用命令时，我都会得到

03-10 10:11:38.704 D/ViewRootImpl(18964): ViewPostImeInputStage ACTION_DOWN
mvx:Diagnostic: 17,87 Showing ViewModel FirstViewModel
03-10 10:11:38.854 I/mono-stdout(18964): mvx:Diagnostic: 17,87 Showing ViewModel FirstViewModel
[0:] mvx:Diagnostic: 17,87 Showing ViewModel FirstViewModel
mvx:Error: 17,91 Failed to create ContentPage FirstPage
03-10 10:11:38.894 I/mono-stdout(18964): mvx:Error: 17,91 Failed to create ContentPage FirstPage
[0:] mvx:Error: 17,91 Failed to create ContentPage FirstPage
mvx:Error: 17,92 Skipping request for FirstViewModel
03-10 10:11:38.904 I/mono-stdout(18964): mvx:Error: 17,92 Skipping request for FirstViewModel
[0:] mvx:Error: 17,92 Skipping request for FirstViewModel`

目前项目是这样的：

启动Activity

[Activity(Label = "Hello MvvmCrossForms", MainLauncher = true)]
public class CrossFormsApp : FormsApplicationActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        //Init forms
        Forms.Init(this, bundle);

        InitialiseMvx();

        //Create mvxformsApp
        var mvxFormsApp = new MvxFormsApp();
        var presenter = Mvx.Resolve<IMvxViewPresenter>() as MvxFormsDroidPagePresenter;

        //Assign the viewPresenter
        presenter.MvxFormsApp = mvxFormsApp;
        LoadApplication(mvxFormsApp);

        //Start mvxApp
        Mvx.Resolve<IMvxAppStart>().Start();
    }

    private void InitialiseMvx()
    {
        if (MvxSingleton<IMvxIoCProvider>.Instance == null)
            Mvx.RegisterSingleton(MvxSimpleIoCContainer.Initialize());

        MvxAndroidSetupSingleton.EnsureSingletonAvailable(this.ApplicationContext)
                                .EnsureInitialized();
    }
}

MainViewModel

public class MainViewModel : MvxViewModel
{
    private string _inputString;

    public ICommand NavigateCommand
    {
        get { return new MvxCommand(() => ShowViewModel<FirstViewModel>()); }
    }

    public string InputString
    {
        get { return _inputString; }
        set { SetProperty(ref _inputString, value); }
    }
}

基本上我要找的是相反的：MvvmCross: How to navigate from regular view to Mvvm viewmodel on Android?

Answer 1

在 MvvmCross 中，ViewPresenter 是处理视图之间导航的组件。

所以我们必须创建自己的

继承自 MvxFormsDroidPagePresenter，因为我们有一个 Forms App
重定向
的非表单调用
- ChangePresentation（常用于Close()）
- Show
到处理活动的 ViewPresenter (MvxAndroidViewPresenter)
非窗体视图模型列表（_androidViews）

class HybridDroidViewPresenter : MvxFormsDroidPagePresenter
{
    private readonly MvxAndroidViewPresenter _androidPesenter;
    private readonly List<Type> _androidViews;
    protected Activity Activity => Mvx.Resolve<IMvxAndroidCurrentTopActivity>().Activity;


    public HybridDroidViewPresenter()
    {
        _androidPesenter = new MvxAndroidViewPresenter();
        _androidViews = new List<Type>
        {
            typeof (FirstViewModel)
        };
    }

    public override void ChangePresentation(MvxPresentationHint hint)
    {
        if (Activity.GetType() != typeof (MainActivity))
        {
            // if we are not on the Forms Activity, we assume, we are on an Android Activity
            _androidPesenter.ChangePresentation(hint);
            return;
        }

        base.ChangePresentation(hint);
    }

    public override void Show(MvxViewModelRequest request)
    {
        if (_androidViews.Contains(request.ViewModelType))
        {
            _androidPesenter.Show(request);
            return;
        }

        base.Show(request);
    }
}

要注册我们的新 ViewPresenter，我们必须在我们的设置中覆盖 CreateViewPresenter

public class Setup : MvxAndroidSetup
{
    // ...

    protected override IMvxAndroidViewPresenter CreateViewPresenter()
    {
        var presenter = new HybridDroidViewPresenter();
        Mvx.RegisterSingleton<IMvxViewPresenter>(presenter);
        return presenter;
    }
}

我们的 ViewPresenter 和 MvxAndroidViewPresenter 需要 IMvxAndroidCurrentTopActivity。所以我们需要让它知道我们MainActivity的生命周期。这可以通过 IMvxAndroidActivityLifetimeListener 并按如下方式修改 Activity 来完成：

[Activity(Label = "MainActivity", ScreenOrientation = ScreenOrientation.Portrait)]
public class MainActivity
    : FormsApplicationActivity
{
    private IMvxAndroidActivityLifetimeListener _lifetimeListener;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        Forms.Init(this, bundle);
        var mvxFormsApp = new MvxFormsApp();
        LoadApplication(mvxFormsApp);

        var presenter = (MvxFormsDroidPagePresenter) Mvx.Resolve<IMvxViewPresenter>();
        presenter.MvxFormsApp = mvxFormsApp;

        Mvx.Resolve<IMvxAppStart>().Start();
        _lifetimeListener = Mvx.Resolve<IMvxAndroidActivityLifetimeListener>();
        _lifetimeListener.OnCreate(this);
    }

    protected override void OnDestroy()
    {
        _lifetimeListener.OnDestroy(this);
        base.OnDestroy();
    }

    protected override void OnNewIntent(Intent intent)
    {
        base.OnNewIntent(intent);
        _lifetimeListener.OnViewNewIntent(this);
    }

    protected override void OnResume()
    {
        base.OnResume();
        _lifetimeListener.OnResume(this);
    }

    protected override void OnPause()
    {
        _lifetimeListener.OnPause(this);
        base.OnPause();
    }

    protected override void OnStart()
    {
        base.OnStart();
        _lifetimeListener.OnStart(this);
    }

    protected override void OnRestart()
    {
        base.OnRestart();
        _lifetimeListener.OnRestart(this);
    }

    protected override void OnStop()
    {
        _lifetimeListener.OnStop(this);
        base.OnStop();
    }
}

现在我们可以通过

导航到我们的FirstViewModel

ShowViewModel<FirstViewModel>()

和 FirstActivity 看起来像一个普通的 MvvMCross Android Activity 并将 FirstView.axml 设置为 ContentView。

[Activity(Label = "FirstActivity")]
public class FirstActivity : MvxActivity<FirstViewModel>
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        SetContentView(Resource.Layout.FirstView);
    }
}

注意事项：

有了这个，你不能从非表单视图导航到表单视图（但到非表单视图），除非通过 Close() 或后退按钮返回
生命周期可能存在一些问题（例如逻辑删除）
MvvMCross 的开发者对 MvvMCross 的 Forms-Support 不满意，因此 Forms Presenter 可能会有一些重大变化

Answer 2

我最终做的是定义一个空接口 IXFViewModel，我在 Forms ViewModels 上实现了它。然后在我的自定义演示器中，我得到了 MvxViewModelRequest.ViewModelType 实现的接口列表。

如果在接口列表中找到类型 IXFViewModel，则扩展 MvxFormsDroidPagePresenter 的自定义演示器会通过调用 base.Show(request) 来处理演示。如果未找到 IXFViewModel 类型，自定义演示器会切换到 MvxAndroidViewPresenter 来处理视图演示。

以下解决方案：

Bootstrap

public class Setup : MvxAndroidSetup
{
    /// prefix ///

    protected override IMvxAndroidViewPresenter CreateViewPresenter()
    {
        var presenter = new XFDroidPresenter();
        Mvx.RegisterSingleton<IMvxViewPresenter>(presenter);
        return presenter;
    }
}

自定义演示者

public class XFDroidPresenter : MvxFormsDroidPagePresenter
{
    protected MvxAndroidViewPresenter DroidPresenter { get; set; }
    protected Activity Activity { get { return Mvx.Resolve<IMvxAndroidCurrentTopActivity>().Activity; } }

    public XFDroidPresenter()
    {
        DroidPresenter = new MvxAndroidViewPresenter();
    }

    public override void ChangePresentation(MvxPresentationHint hint)
    {
        if(Activity.GetType() != typeof(CrossFormsApp))
        {
            DroidPresenter.ChangePresentation(hint);
            return;
        }

        base.ChangePresentation(hint);
    }

    public override void Show(MvxViewModelRequest request)
    {
        var implementedInterfaces = request.ViewModelType
                                           .GetInterfaces()
                                           .ToList();

        if (!implementedInterfaces.Contains(typeof(IXFViewModel)))
        {
            DroidPresenter.Show(request);
            return;
        }

        base.Show(request);
    }
}

启动器和表单 Activity

[Activity(Label = "Hello MvvmCrossForms", Icon = "@drawable/icon", MainLauncher = true)]
public class CrossFormsApp : FormsApplicationActivity
{
    private MvxAndroidLifetimeMonitor _lifeTimeMonitor;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        Forms.Init(this, bundle);

        InitialiseMvx();

        var mvxFormsApp = new MvxFormsApp();
        var presenter = Mvx.Resolve<IMvxViewPresenter>() as MvxFormsDroidPagePresenter;

        presenter.MvxFormsApp = mvxFormsApp;
        LoadApplication(mvxFormsApp);
        Mvx.Resolve<IMvxAppStart>().Start();

        _lifeTimeMonitor = Mvx.Resolve<IMvxAndroidCurrentTopActivity>() as MvxAndroidLifetimeMonitor;
        _lifeTimeMonitor.OnCreate(this);
    }

    private void InitialiseMvx()
    {
        if (MvxSingleton<IMvxIoCProvider>.Instance == null)
            Mvx.RegisterSingleton(MvxSimpleIoCContainer.Initialize());

        MvxAndroidSetupSingleton.EnsureSingletonAvailable(this.ApplicationContext)
                                .EnsureInitialized();
    }

    protected override void OnStart()
    {
        base.OnStart ();
        _lifeTimeMonitor.OnStart(this);
    }

    protected override void OnRestart()
    {
        base.OnRestart ();
        _lifeTimeMonitor.OnRestart(this);
    }

    protected override void OnResume()
    {
        base.OnResume ();
        _lifeTimeMonitor.OnResume(this);
    }

    protected override void OnDestroy()
    {
        base.OnDestroy ();
        _lifeTimeMonitor.OnDestroy(this);
    }
}

界面和 ViewModel

public interface IXFViewModel
{
}

public class MainViewModel : MvxViewModel, IXFViewModel
{
    private string _inputString;

    public ICommand NavigateCommand
    {
        get { return new MvxCommand(() => Close(this)); }
    }

    public string InputString
    {
        get { return _inputString; }
        set { SetProperty(ref _inputString, value); }
    }
}

MvvmCross：混合 Xamarin.Forms 和 Android Activity 应用

MvvmCross: Hybrid Xamarin.Forms and Android Activity Application

mvvm

xamarin

mvvmcross

xamarin.forms

view-model-pattern