App.xaml

<Application
    x:Class="ReactInUWP.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
	xmlns:local="using:ReactInUWP">
    
</Application>

App.xaml.cs

using System;
using Windows.ApplicationModel;
using Windows.ApplicationModel.Activation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
using Microsoft.Gaming.XboxGameBar;


namespace ReactInUWP
{
    sealed partial class App : Application
    {
        private XboxGameBarWidget widget1 = null;

        public App()
        {
            this.InitializeComponent();
            this.Suspending += OnSuspending;
        }

        protected override void OnActivated(IActivatedEventArgs args)
        {
            XboxGameBarWidgetActivatedEventArgs widgetArgs = null;
            if (args.Kind == ActivationKind.Protocol)
            {
                var protocolArgs = args as IProtocolActivatedEventArgs;
                string scheme = protocolArgs.Uri.Scheme;
                if (scheme.Equals("ms-gamebarwidget"))
                {
                    widgetArgs = args as XboxGameBarWidgetActivatedEventArgs;
                }
            }
            if (widgetArgs != null)
            {
                if (widgetArgs.IsLaunchActivation)
                {
                    var rootFrame = new Frame();
                    rootFrame.NavigationFailed += OnNavigationFailed;
                    Window.Current.Content = rootFrame;

                    widget1 = new XboxGameBarWidget(
                        widgetArgs,
                        Window.Current.CoreWindow,
                        rootFrame);
                    rootFrame.Navigate(typeof(ReactControl));

                    Window.Current.Closed += Widget1Window_Closed;

                    Window.Current.Activate();
                }

            }
        }
        private void Widget1Window_Closed(object sender, Windows.UI.Core.CoreWindowEventArgs e)
        {
            widget1 = null;
            Window.Current.Closed -= Widget1Window_Closed;
        }

        protected override void OnLaunched(LaunchActivatedEventArgs e)
        {
            Frame rootFrame = Window.Current.Content as Frame;

            if (rootFrame == null)
            {
                rootFrame = new Frame();

                rootFrame.NavigationFailed += OnNavigationFailed;


                Window.Current.Content = rootFrame;
            }

            if (e.PrelaunchActivated == false)
            {
                if (rootFrame.Content == null)
                {
                    rootFrame.Navigate(typeof(ReactControl), e.Arguments);
                }
                Window.Current.Activate();
            }
        }

        void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
        {
            throw new Exception("Failed to load Page " + e.SourcePageType.FullName);
        }

        private void OnSuspending(object sender, SuspendingEventArgs e)
        {
            var deferral = e.SuspendingOperation.GetDeferral();

            widget1 = null;

            deferral.Complete();
        }
    }
}

ReactControl.xaml

<Page
    x:Class="ReactInUWP.ReactControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:ReactInUWP"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
	xmlns:react="using:Microsoft.ReactNative"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <Grid>
        <react:ReactRootView x:Name="RootElement" />
    </Grid>
</Page>

ReactControl.xaml.cs

using Microsoft.ReactNative;
using Microsoft.ReactNative.Managed;
using Windows.UI.Xaml.Controls;

namespace ReactInUWP
{
    sealed partial class ReactControl : Page
    {
        static readonly string JSFileName = "index";
        static readonly string JSComponentName = "ReactInUWP";

        public ReactControl()
        {
            InitializeComponent();
            LoadReact();
        }

        public void LoadReact()
        {
            ReactNativeHost host = new ReactNativeHost();

            host.InstanceSettings.MainComponentName = JSFileName;
            host.InstanceSettings.JavaScriptMainModuleName = JSFileName;
            host.InstanceSettings.UseLiveReload = true;
            host.InstanceSettings.UseWebDebugger = true;
            host.InstanceSettings.EnableDeveloperMenu = true;
            host.ReloadInstance();

            RootElement.ComponentName = JSComponentName;
            JSValue initialProps = new JSValueObject { ["one"] = "1", ["two"] = "2" };
            RootElement.InitialProps = (IJSValueWriter writer) => writer.WriteValue(initialProps);
            RootElement.ReactNativeHost = host;
        }
    }
}