先理解UWP应用程序完整生命周期需要经历如下状态：

1、应用程序第一次被开启，状态由 NotRunning 被激活（Activated）为 Running；
2、当用户点击 Start 按钮或者切换到其他应用，状态由 Running 暂停（Suspending）为Suspended；
3、当用户再次激活应用（如点击磁贴、任务切换、Toast 通知等），状态由 Suspended 恢复（Resuming）为 Running；
4、如果应用在 Suspended 状态下内存不足，系统会自动将应用程序终止（Terminate），状态由 Suspended变为 Not Running；
5、用户可以使用任务管理器强制关闭某个应用程序（CloseByUser），那么此时应用程序的状态也是由Suspended 变为 Not Running。
当应用处于关闭状态下，点击推送通知会触发激活应用，而此时应用如果已经关闭，所以停留在启动界面

image

解决办法：重写App类的OnActivated方法，首先判断启动类型如果是推送通知，再次执行一次启动OnLaunched中的方法

下面是完整的推送通知代码：

image

using Microsoft.Services.Store.Engagement;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.ApplicationModel;
using Windows.ApplicationModel.Activation;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

namespace App1
{
    /// <summary>
    /// Provides application-specific behavior to supplement the default Application class.
    /// </summary>
    sealed partial class App : Application
    {
        /// <summary>
        /// Initializes the singleton application object.  This is the first line of authored code
        /// executed, and as such is the logical equivalent of main() or WinMain().
        /// </summary>
        public App()
        {
            this.InitializeComponent();
            this.Suspending += OnSuspending;
            RegisterEngagementNotification();
        }
        private async void RegisterEngagementNotification()
        {

            StoreServicesEngagementManager engagementManager = StoreServicesEngagementManager.GetDefault();
            await engagementManager.UnregisterNotificationChannelAsync();
            await engagementManager.RegisterNotificationChannelAsync();
        }
        protected override void OnActivated(IActivatedEventArgs args)
        {
            base.OnActivated(args);
            if (args.Kind == ActivationKind.ToastNotification)
            {
                var toastArgs = args as ToastNotificationActivatedEventArgs;
                var arguments = toastArgs.Argument;

                if (arguments == "ARG")
                {
                    Frame rootFrame = Window.Current.Content as Frame;
                    if (rootFrame == null)
                    {
                        rootFrame = new Frame();
                        Window.Current.Content = rootFrame;
                    }
                    rootFrame.Navigate(typeof(MainPage));
                    Window.Current.Activate();
                }
            }
        }
        /// <summary>
        /// Invoked when the application is launched normally by the end user.  Other entry points
        /// will be used such as when the application is launched to open a specific file.
        /// </summary>
        /// <param name="e">Details about the launch request and process.</param>
        protected override void OnLaunched(LaunchActivatedEventArgs e)
        {
#if DEBUG
            if (System.Diagnostics.Debugger.IsAttached)
            {
                this.DebugSettings.EnableFrameRateCounter = true;
            }
#endif
            Frame rootFrame = Window.Current.Content as Frame;

            // Do not repeat app initialization when the Window already has content,
            // just ensure that the window is active
            if (rootFrame == null)
            {
                // Create a Frame to act as the navigation context and navigate to the first page
                rootFrame = new Frame();

                rootFrame.NavigationFailed += OnNavigationFailed;

                if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
                {
                    //TODO: Load state from previously suspended application
                }

                // Place the frame in the current Window
                Window.Current.Content = rootFrame;
            }

            if (e.PrelaunchActivated == false)
            {
                if (rootFrame.Content == null)
                {
                    // When the navigation stack isn't restored navigate to the first page,
                    // configuring the new page by passing required information as a navigation
                    // parameter
                    rootFrame.Navigate(typeof(MainPage), e.Arguments);
                }
                // Ensure the current window is active
                Window.Current.Activate();
            }
        }

        /// <summary>
        /// Invoked when Navigation to a certain page fails
        /// </summary>
        /// <param name="sender">The Frame which failed navigation</param>
        /// <param name="e">Details about the navigation failure</param>
        void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
        {
            throw new Exception("Failed to load Page " + e.SourcePageType.FullName);
        }

        /// <summary>
        /// Invoked when application execution is being suspended.  Application state is saved
        /// without knowing whether the application will be terminated or resumed with the contents
        /// of memory still intact.
        /// </summary>
        /// <param name="sender">The source of the suspend request.</param>
        /// <param name="e">Details about the suspend request.</param>
        private void OnSuspending(object sender, SuspendingEventArgs e)
        {
            var deferral = e.SuspendingOperation.GetDeferral();
            //TODO: Save application state and stop any background activity
            deferral.Complete();
        }
    }
}