Problem Checking if File Exists When App is Launched

Question

I'm developing an app which checks a file "lastuser.txt" to determine which database to open, as sometimes people share phones. Anyway, I'm trying to call  TryGetItemAsync() in the OnLaunched() section in App.xaml.cs but I get the message
"The name 'TryGetItemAsync' does not exist in the current context".  I am new to C# and phone app development. Any help would be greatly appreciated. Below is my code:
tia
CS
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using SQLite;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Storage;
using System.Threading.Tasks;
using System.Diagnostics;
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.Media.Animation;
using Windows.UI.Xaml.Navigation;
// The Blank Application template is documented at http://go.microsoft.com/fwlink/?LinkId=391641
namespace BP_Alert
/// <summary>
/// Provides application-specific behavior to supplement the default Application class.
/// </summary>
public sealed partial class App : Application
public static string DBPath = string.Empty;
public static string LastUser = string.Empty;
public static DateTime Time_Taken { get; set; }
private TransitionCollection transitions;
/// <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 += this.OnSuspending;
/// <summary>
/// Invoked when the application is launched normally by the end user. Other entry points
/// will be used when the application is launched to open a specific file, to display
/// search results, and so forth.
/// </summary>
/// <param name="e">Details about the launch request and process.</param>
protected async 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();
// TODO: change this value to a cache size that is appropriate for your application
rootFrame.CacheSize = 1;
if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
// TODO: Load state from previously suspended application
DBPath = Windows.Storage.ApplicationData.Current.LocalFolder.Path;
LastUser = Path.Combine(Windows.Storage.ApplicationData.Current.LocalFolder.Path,"LastUser.txt");
bool result = await TryGetItemAsync(LastUser); <--Error!!!!!!!!!!!!!!!
// Place the frame in the current Window
Window.Current.Content = rootFrame;

Answer 1

It seems that TryGetItemAsync is a method on a StorageFolder, so you will need to do something like:
myStorageFolder.TryGetItemAsync(LastUser);
See here:
https://msdn.microsoft.com/en-us/library/windows/apps/windows.storage.storagefolder.trygetitemasync.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1
If you go to that link and scroll down to the bottom of the page, it says:
Minimum supported phone
None supported