c# - Xamarin Forms/ReactiveUI Router-在关闭 subview 后显示 subview 并执行父ViewModel代码

Question

在我的父ViewModel中，我使用以下代码通过ReactiveUI的路由导航到ChildView

appBootstrapper.Router.Navigate.Execute(new ChildViewModel(HostScreen)).Subscribe();

此代码按预期方式工作。

但是，当关闭 subview 时，我想执行一些额外的操作(让我们使用通过bool ViewModel属性隐藏 Activity 指示器的示例)，例如

ShowActivityIndicator = true;
appBootstrapper.Router.Navigate.Execute(new ChildViewModel(HostScreen)).Subscribe();
ShowActivityIndicator = false;

由于显示了 subview ，因此该代码未按预期执行，然后立即执行 ShowActivityIndicator = false;。

我如何重写代码，以便在关闭并关闭 ShowActivityIndicator = false;之后执行 ？谢谢!

更新

感谢Glenn的建议，我尝试使用ChildView技术，但是lambda代码从不执行。我的代码如下...

var microsoftSignInVM = new ViewModel.MicrosoftSignInVM(HostScreen);
//
microsoftSignInVM.WhenNavigatingFromObservable().Subscribe((_) =>
{
    ShowActivityIndicator = true;
    //
    Data.Synchronisation.SynchroniseLocalDataCacheAsync();
    //
    appBootstrapper.Router.Navigate.Execute(new ViewModel.SelectJobVM(HostScreen)).Subscribe();
    //
    ShowActivityIndicator = false;
});
//
appBootstrapper.Router.Navigate.Execute(microsoftSignInVM).Subscribe();

我在lambda中放置了一个断点，但它从未被击中。

更新2-更新

我创建了几个最小的测试类。 这些在WPF项目中有效的方法，但是不能使用XAMARIN格式 ...

共享

TestAV.xaml.cs

namespace TestApp.Test
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class TestAV : ReactiveContentPage<TestAVM>
    {
        public TestAV()
        {
            InitializeComponent();
                //
                this.WhenActivated(
                    disposables =>
                    {
                        this.BindCommand(this.ViewModel, x => x.ClickCommand, x => x.button)
                            .DisposeWith(disposables);
                    });
        }
    }
}

TestAVM.cs

namespace TestApp.Test
{
    public class TestAVM : ReactiveObject, IEnableLogger, IRoutableViewModel
    {
        public TestAVM(IScreen hostScreen)
        {
            _HostScreen = hostScreen;
            //
            TestBVM testBVM = new TestBVM(_HostScreen);
            //
            _ClickCommand = ReactiveCommand.CreateFromObservable(() => _HostScreen.Router.Navigate.Execute(testBVM).Select(_ => Unit.Default));
            //
            testBVM.WhenNavigatingFromObservable().Subscribe((_) =>
            {
                ShowActivityIndicator = true;
            });
        }
        //
        public bool ShowActivityIndicator { get; set; }
        //
        private readonly ReactiveCommand<Unit, Unit> _ClickCommand; public ReactiveCommand<Unit, Unit> ClickCommand => _ClickCommand;
        //
        private readonly IScreen _HostScreen; public IScreen HostScreen => _HostScreen;
        //
        public string UrlPathSegment => "TestA";
    }
}

TestBV.xaml.cs

namespace TestApp.Test
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class TestBV : ReactiveContentPage<TestBVM>
    {
        public TestBV()
        {
            InitializeComponent();
            //
            this.WhenActivated(
                disposables =>
                {
                    this
                        .BindCommand(this.ViewModel, x => x.ClickCommand, x => x.button)
                        .DisposeWith(disposables);
                });
        }
    }
}

TestBVM.cs

namespace TestApp.Test
{
    public class TestBVM : ReactiveObject, IEnableLogger, IRoutableViewModel
    {
        public TestBVM(IScreen hostScreen)
        {
            _HostScreen = hostScreen;
        }
        //
        public ReactiveCommand<Unit, Unit> ClickCommand => _HostScreen.Router.NavigateBack;
        //
        private readonly IScreen _HostScreen; public IScreen HostScreen => _HostScreen;
        //
        public string UrlPathSegment => "TestB";
    }
}

Xamarin特定文件

AppBootstrapper.cs

namespace TestApp
{
    public class AppBootstrapper : ReactiveObject, IScreen
    {
        public AppBootstrapper(IMutableDependencyResolver dependencyResolver = null, RoutingState router = null)
        {
            Router = router ?? new RoutingState();
            //
            RegisterParts(dependencyResolver ?? Locator.CurrentMutable);
            //
            Router.Navigate.Execute(new Test.TestAVM(this));
        }

        public RoutingState Router { get; private set; }

        private void RegisterParts(IMutableDependencyResolver dependencyResolver)
        {
            dependencyResolver.RegisterConstant(this, typeof(IScreen));
            //
            dependencyResolver.Register(() => new Test.TestAV(), typeof(IViewFor<Test.TestAVM>));
            dependencyResolver.Register(() => new Test.TestBV(), typeof(IViewFor<Test.TestBVM>));
        }

        public Page CreateMainPage()
        {
            return new RoutedViewHost();
        }
    }
}

TestAV.xaml

<?xml version="1.0" encoding="utf-8" ?>
<rxui:ReactiveContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                           xmlns:rxui="clr-namespace:ReactiveUI.XamForms;assembly=ReactiveUI.XamForms"
                          xmlns:vm="clr-namespace:TestApp.Test"
                          x:TypeArguments="vm:TestAVM"
                        x:Class="TestApp.Test.TestAV">
    <ContentPage.Content>
        <StackLayout>
            <Button x:Name="button" Text="click A" HorizontalOptions="CenterAndExpand" />
        </StackLayout>
    </ContentPage.Content>
</rxui:ReactiveContentPage>

TestBV.xaml

<?xml version="1.0" encoding="utf-8" ?>
<rxui:ReactiveContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                           xmlns:rxui="clr-namespace:ReactiveUI.XamForms;assembly=ReactiveUI.XamForms"
                          xmlns:vm="clr-namespace:TestApp.Test"
                          x:TypeArguments="vm:TestBVM"
             x:Class="TestApp.Test.TestBV">
    <ContentPage.Content>
        <StackLayout>
            <Button x:Name="button" Text="click B" HorizontalOptions="CenterAndExpand" />
        </StackLayout>
    </ContentPage.Content>
</rxui:ReactiveContentPage>

WPF特定文件

TestAV.xaml

<rxui:ReactiveUserControl x:Class="TestApp.TestAV"
            x:TypeArguments="vm:TestAVM"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:rxui="http://reactiveui.net"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:vm="clr-namespace:TestApp.Test">
    <Grid>
        <Button x:Name="button" Content="click A" />
    </Grid>
</rxui:ReactiveUserControl>

TestBV.xaml

<rxui:ReactiveUserControl x:Class="TestApp.TestBV"
            x:TypeArguments="vm:TestBVM"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:rxui="http://reactiveui.net"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:vm="clr-namespace:TestApp.Test">
    <Grid>
        <Button x:Name="button" Content="click B" />
    </Grid>
</rxui:ReactiveUserControl>

值得注意的是，如果我使用

_ClickCommand = ReactiveCommand.CreateFromObservable(() => _HostScreen.Router.Navigate.Execute(new TestAVM()).Select(_ => Unit.Default));

在 TestBVM.cs 中，则lambda会按预期触发。

Xamarin Forms实现WhenNavigatingFromObservable().Subscribe(...)似乎有问题，但是我愿意接受其他观察!

Answer 1

您可以采用几种不同的方法来处理它。

路由器具有几个可观察对象，您可以在调用导航堆栈上的操作时进行订阅。您可以使用RoutableViewModelMixin中还有一个扩展方法WhenNavigatingFromObservable。

public void ShowChildView()
{
    ShowActivityIndicator = true;
    var childViewModel = new ChildViewModel(HostScreen);
    // Use the extension method to get an observable when the child view is navigated away from, subscribe and set the variable.
    childViewModel.WhenNavigatingFromObservable().Subscribe(x => ShowActivityIndicator = false);
    appBootstrapper.Router.Navigate.Execute(childViewModel).Subscribe();
} 

第二种选择，如果您不介意 child 身上发生的功能，则可以使用WhenActivated()机制

public ChildView()
{
    this.WhenActivated(disposable => 
     {
        // do activation logic.
        return new[] { Disposable.Create(() => DoDeactivationLogic());
     }

此处有更多详细信息 https://reactiveui.net/docs/handbook/when-activated/