c# - Xamarin Forms/ReactiveUI Router - 关闭子视图后显示子视图并执行父视图模型代码

Question

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

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

此代码按预期工作。

但是，当子视图关闭时，我想执行一些额外的操作（让我们使用通过 bool ViewModel 属性隐藏活动指示器的示例），例如

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

此代码未按预期执行，因为显示了子视图，然后ShowActivityIndicator = false;立即执行。

如何重写代码以便在关闭后ShowActivityIndicator = false;执行？谢谢！ChildView

---

更新

感谢 Glenn 的建议，我尝试使用该WhenNavigatingFromObservable().Subscribe(...)技术，但 lambda 代码从未执行。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，它永远不会被击中。

---

更新 2 - 更新

我创建了几个最小的测试类。这些在 WPF 项目中可以正常工作，但不能使用 XAMARIN 表单...

共享

测试AV.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);
                    });
        }
    }
}

测试AVM.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";
    }
}

测试BV.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);
                });
        }
    }
}

测试BVM.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();
        }
    }
}

测试AV.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>

测试BV.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

测试AV.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>

测试BV.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，然后 lambda 按预期触发。

似乎 Xamarin Forms 的实现存在问题Router.NavigateBack，但我愿意接受其他意见！

标签： c#mvvmxamarin.formsreactive-programmingreactiveui

Answer 1

您可以通过几种不同的方式来处理它。

当调用导航堆栈上的操作时，Router 有几个可以订阅的 observable。您还可以使用一个RoutableViewModelMixin名为的扩展方法。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，如果您不介意孩子身上发生的功能，您可以使用 WhenActivated() 机制

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

更多细节在这里https://reactiveui.net/docs/handbook/when-activated/