Enable Nullable for #4473. (#4544)

* Enable Nullable for #4473.

* Fixed bug.

* Fixed indentation bug.

* Fixed line spacing issue.

* Fixed line spacing issue.

* Fixed line spacing issue.

code/TemplateStudioForWinUICs/Templates/Ft/SettingsStorage/Param_ProjectName/Contracts/Services/ILocalSettingsService.cs

@@ -2,7 +2,7 @@
 
 public interface ILocalSettingsService
 {
-    Task<T> ReadSettingAsync<T>(string key);
+    Task<T?> ReadSettingAsync<T>(string key);
 
     Task SaveSettingAsync<T>(string key, T value);
 }

code/TemplateStudioForWinUICs/Templates/Ft/SettingsStorage/Param_ProjectName/Helpers/SettingsStorageExtensions.cs

@@ -23,7 +23,7 @@ public static class SettingsStorageExtensions
         await FileIO.WriteTextAsync(file, fileContent);
     }
 
-    public static async Task<T> ReadAsync<T>(this StorageFolder folder, string name)
+    public static async Task<T?> ReadAsync<T>(this StorageFolder folder, string name)
     {
         if (!File.Exists(Path.Combine(folder.Path, GetFileName(name))))
         {
@@ -46,9 +46,9 @@ public static class SettingsStorageExtensions
         settings.Values[key] = value;
     }
 
-    public static async Task<T> ReadAsync<T>(this ApplicationDataContainer settings, string key)
+    public static async Task<T?> ReadAsync<T>(this ApplicationDataContainer settings, string key)
     {
-        object obj;
+        object? obj;
 
         if (settings.Values.TryGetValue(key, out obj))
         {
@@ -75,7 +75,7 @@ public static class SettingsStorageExtensions
         return storageFile;
     }
 
-    public static async Task<byte[]> ReadFileAsync(this StorageFolder folder, string fileName)
+    public static async Task<byte[]?> ReadFileAsync(this StorageFolder folder, string fileName)
     {
         var item = await folder.TryGetItemAsync(fileName).AsTask().ConfigureAwait(false);
 
@@ -89,7 +89,7 @@ public static class SettingsStorageExtensions
         return null;
     }
 
-    public static async Task<byte[]> ReadBytesAsync(this StorageFile file)
+    public static async Task<byte[]?> ReadBytesAsync(this StorageFile file)
     {
         if (file != null)
         {

code/TemplateStudioForWinUICs/Templates/Ft/SettingsStorage/Param_ProjectName/Models/LocalSettingsOptions.cs

@@ -2,12 +2,12 @@
 
 public class LocalSettingsOptions
 {
-    public string ApplicationDataFolder
+    public string? ApplicationDataFolder
     {
         get; set;
     }
 
-    public string LocalSettingsFile
+    public string? LocalSettingsFile
     {
         get; set;
     }

code/TemplateStudioForWinUICs/Templates/Ft/SettingsStorage/Param_ProjectName/Services/LocalSettingsServicePackaged.cs

@@ -6,7 +6,7 @@ namespace Param_RootNamespace.Services;
 
 public class LocalSettingsServicePackaged : ILocalSettingsService
 {
-    public async Task<T> ReadSettingAsync<T>(string key)
+    public async Task<T?> ReadSettingAsync<T>(string key)
     {
         if (ApplicationData.Current.LocalSettings.Values.TryGetValue(key, out var obj))
         {

code/TemplateStudioForWinUICs/Templates/Ft/SettingsStorage/Param_ProjectName/Services/LocalSettingsServiceUnpackaged.cs

@@ -8,35 +8,48 @@ namespace Param_RootNamespace.Services;
 
 public class LocalSettingsServiceUnpackaged : ILocalSettingsService
 {
+    private const string _defaultApplicationDataFolder = "Param_ProjectName/ApplicationData";
+    private const string _defaultLocalSettingsFile = "LocalSettings.json";
+
     private readonly IFileService _fileService;
     private readonly LocalSettingsOptions _options;
-    private readonly string _localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+
+    private readonly string _localApplicationData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+    private readonly string _applicationDataFolder;
+    private readonly string _localsettingsFile;
 
     private IDictionary<string, object> _settings;
 
+    private bool _isInitialized;
+
     public LocalSettingsServiceUnpackaged(IFileService fileService, IOptions<LocalSettingsOptions> options)
     {
         _fileService = fileService;
         _options = options.Value;
+
+        _applicationDataFolder = Path.Combine(_localApplicationData, _options.ApplicationDataFolder ?? _defaultApplicationDataFolder);
+        _localsettingsFile = _options.LocalSettingsFile ?? _defaultLocalSettingsFile;
+
+        _settings = new Dictionary<string, object>();
     }
 
     private async Task InitializeAsync()
     {
-        if (_settings is null)
+        if (!_isInitialized)
         {
-            var folderPath = Path.Combine(_localAppData, _options.ApplicationDataFolder);
-            var fileName = _options.LocalSettingsFile;
-            _settings = await Task.Run(() => _fileService.Read<IDictionary<string, object>>(folderPath, fileName)) ?? new Dictionary<string, object>();
+            _settings = await Task.Run(() => _fileService.Read<IDictionary<string, object>>(_applicationDataFolder, _localsettingsFile)) ?? new Dictionary<string, object>();
+
+            _isInitialized = true;
         }
     }
 
-    public async Task<T> ReadSettingAsync<T>(string key)
+    public async Task<T?> ReadSettingAsync<T>(string key)
     {
         await InitializeAsync();
 
-        object obj;
+        object? obj;
 
-        if (_settings.TryGetValue(key, out obj))
+        if (_settings != null && _settings.TryGetValue(key, out obj))
         {
             return await Json.ToObjectAsync<T>((string)obj);
         }
@@ -50,8 +63,6 @@ public class LocalSettingsServiceUnpackaged : ILocalSettingsService
 
         _settings[key] = await Json.StringifyAsync(value);
 
-        var folderPath = Path.Combine(_localAppData, _options.ApplicationDataFolder);
-        var fileName = _options.LocalSettingsFile;
-        await Task.Run(() => _fileService.Save(folderPath, fileName, _settings));
+        await Task.Run(() => _fileService.Save(_applicationDataFolder, _localsettingsFile, _settings));
     }
 }

code/TemplateStudioForWinUICs/Templates/Pg/CGrid/Param_ProjectName/ViewModels/Param_ItemNameDetailViewModel.cs

@@ -7,9 +7,9 @@ namespace Param_RootNamespace.ViewModels;
 public class Param_ItemNameDetailViewModel : ObservableRecipient, INavigationAware
 {
     private readonly ISampleDataService _sampleDataService;
-    private SampleOrder _item;
+    private SampleOrder? _item;
 
-    public SampleOrder Item
+    public SampleOrder? Item
     {
         get => _item;
         set => SetProperty(ref _item, value);

code/TemplateStudioForWinUICs/Templates/Pg/CGrid/Param_ProjectName/ViewModels/Param_ItemNameViewModel.cs

@@ -11,9 +11,11 @@ public class Param_ItemNameViewModel : ObservableRecipient, INavigationAware
 {
     private readonly INavigationService _navigationService;
     private readonly ISampleDataService _sampleDataService;
-    private ICommand _itemClickCommand;
 
-    public ICommand ItemClickCommand => _itemClickCommand ??= new RelayCommand<SampleOrder>(OnItemClick);
+    public ICommand ItemClickCommand
+    {
+        get;
+    }
 
     public ObservableCollection<SampleOrder> Source { get; } = new ObservableCollection<SampleOrder>();
 
@@ -21,6 +23,8 @@ public class Param_ItemNameViewModel : ObservableRecipient, INavigationAware
     {
         _navigationService = navigationService;
         _sampleDataService = sampleDataService;
+
+        ItemClickCommand = new RelayCommand<SampleOrder>(OnItemClick);
     }
 
     public async void OnNavigatedTo(object parameter)
@@ -39,12 +43,12 @@ public class Param_ItemNameViewModel : ObservableRecipient, INavigationAware
     {
     }
 
-    private void OnItemClick(SampleOrder clickedItem)
+    private void OnItemClick(SampleOrder? clickedItem)
     {
         if (clickedItem != null)
         {
             _navigationService.SetListDataItemForNextConnectedAnimation(clickedItem);
-            _navigationService.NavigateTo(typeof(Param_ItemNameDetailViewModel).FullName, clickedItem.OrderID);
+            _navigationService.NavigateTo(typeof(Param_ItemNameDetailViewModel).FullName!, clickedItem.OrderID);
         }
     }
 }

code/TemplateStudioForWinUICs/Templates/Pg/CGrid/Param_ProjectName/Views/Param_ItemNameDetailPage.xaml.cs

@@ -24,8 +24,12 @@ public sealed partial class Param_ItemNameDetailPage : Page
         base.OnNavigatingFrom(e);
         if (e.NavigationMode == NavigationMode.Back)
         {
-            var navigationService = App.GetService<INavigationService>();
-            navigationService.SetListDataItemForNextConnectedAnimation(ViewModel.Item);
+            var navigationService = App.GetService<INavigationService>()!;
+
+            if (ViewModel.Item != null)
+            {
+                navigationService.SetListDataItemForNextConnectedAnimation(ViewModel.Item);
+            }
         }
     }
 }

code/TemplateStudioForWinUICs/Templates/Pg/List/Param_ProjectName/ViewModels/Param_ItemNameViewModel.cs

@@ -9,9 +9,9 @@ namespace Param_RootNamespace.ViewModels;
 public class Param_ItemNameViewModel : System.ComponentModel.INotifyPropertyChanged, INavigationAware
 {
     private readonly ISampleDataService _sampleDataService;
-    private SampleOrder _selected;
+    private SampleOrder? _selected;
 
-    public SampleOrder Selected
+    public SampleOrder? Selected
     {
         get => _selected;
         set => SetProperty(ref _selected, value);

code/TemplateStudioForWinUICs/Templates/Pg/List/Param_ProjectName/Views/Param_ItemNameDetailControl.xaml.cs

@@ -6,7 +6,7 @@ namespace Param_RootNamespace.Views;
 
 public sealed partial class Param_ItemNameDetailControl : UserControl
 {
-    public SampleOrder ListDetailsMenuItem
+    public SampleOrder? ListDetailsMenuItem
     {
         get => GetValue(ListDetailsMenuItemProperty) as SampleOrder;
         set => SetValue(ListDetailsMenuItemProperty, value);
@@ -21,7 +21,9 @@ public sealed partial class Param_ItemNameDetailControl : UserControl
 
     private static void OnListDetailsMenuItemPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
-        var control = d as Param_ItemNameDetailControl;
-        control.ForegroundElement.ChangeView(0, 0, 1);
+        if (d is Param_ItemNameDetailControl control)
+        {
+            control.ForegroundElement.ChangeView(0, 0, 1);
+        }
     }
 }

code/TemplateStudioForWinUICs/Templates/Pg/Settings/ViewModels/Param_ItemNameViewModel.cs

@@ -9,6 +9,7 @@ public class Param_ItemNameViewModel : System.ComponentModel.INotifyPropertyChan
 {
     private readonly IThemeSelectorService _themeSelectorService;
     private ElementTheme _elementTheme;
+    private string _versionDescription;
 
     public ElementTheme ElementTheme
     {
@@ -16,42 +17,32 @@ public class Param_ItemNameViewModel : System.ComponentModel.INotifyPropertyChan
         set => SetProperty(ref _elementTheme, value);
     }
 
-    private string _versionDescription;
-
     public string VersionDescription
     {
         get => _versionDescription;
         set => SetProperty(ref _versionDescription, value);
     }
 
-    private ICommand _switchThemeCommand;
-
     public ICommand SwitchThemeCommand
     {
-        get
-        {
-            if (_switchThemeCommand == null)
-            {
-                _switchThemeCommand = new RelayCommand<ElementTheme>(
-                    async (param) =>
-                    {
-                        if (ElementTheme != param)
-                        {
-                            ElementTheme = param;
-                            await _themeSelectorService.SetThemeAsync(param);
-                        }
-                    });
-            }
-
-            return _switchThemeCommand;
-        }
+        get;
     }
 
     public Param_ItemNameViewModel(IThemeSelectorService themeSelectorService)
     {
         _themeSelectorService = themeSelectorService;
         _elementTheme = _themeSelectorService.Theme;
-        VersionDescription = GetVersionDescription();
+        _versionDescription = GetVersionDescription();
+
+        SwitchThemeCommand = new RelayCommand<ElementTheme>(
+            async (param) =>
+            {
+                if (ElementTheme != param)
+                {
+                    ElementTheme = param;
+                    await _themeSelectorService.SetThemeAsync(param);
+                }
+            });
     }
 
     private static string GetVersionDescription()

code/TemplateStudioForWinUICs/Templates/Pg/WebView/Contracts/Services/IWebViewService.cs

@@ -5,6 +5,11 @@ namespace Param_RootNamespace.Contracts.Services;
 
 public interface IWebViewService
 {
+    Uri? Source
+    {
+        get;
+    }
+
     bool CanGoBack
     {
         get;
@@ -15,7 +20,7 @@ public interface IWebViewService
         get;
     }
 
-    event EventHandler<CoreWebView2WebErrorStatus> NavigationCompleted;
+    event EventHandler<CoreWebView2WebErrorStatus>? NavigationCompleted;
 
     void Initialize(WebView2 webView);
 

code/TemplateStudioForWinUICs/Templates/Pg/WebView/Services/WebViewService.cs

@@ -1,4 +1,5 @@
-using Microsoft.UI.Xaml.Controls;
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.UI.Xaml.Controls;
 using Microsoft.Web.WebView2.Core;
 using Param_RootNamespace.Contracts.Services;
 
@@ -6,31 +7,42 @@ namespace Param_RootNamespace.Services;
 
 public class WebViewService : IWebViewService
 {
-    private WebView2 _webView;
+    private WebView2? _webView;
 
-    public bool CanGoBack => _webView.CanGoBack;
+    public Uri? Source => _webView?.Source;
 
-    public bool CanGoForward => _webView.CanGoForward;
+    [MemberNotNullWhen(true, nameof(_webView))]
+    public bool CanGoBack => _webView != null && _webView.CanGoBack;
 
-    public event EventHandler<CoreWebView2WebErrorStatus> NavigationCompleted;
+    [MemberNotNullWhen(true, nameof(_webView))]
+    public bool CanGoForward => _webView != null && _webView.CanGoForward;
+
+    public event EventHandler<CoreWebView2WebErrorStatus>? NavigationCompleted;
 
     public WebViewService()
     {
     }
 
+    [MemberNotNull(nameof(_webView))]
     public void Initialize(WebView2 webView)
     {
         _webView = webView;
         _webView.NavigationCompleted += OnWebViewNavigationCompleted;
     }
 
-    public void GoBack() => _webView.GoBack();
+    public void GoBack() => _webView?.GoBack();
 
-    public void GoForward() => _webView.GoForward();
+    public void GoForward() => _webView?.GoForward();
 
-    public void Reload() => _webView.Reload();
+    public void Reload() => _webView?.Reload();
 
-    public void UnregisterEvents() => _webView.NavigationCompleted -= OnWebViewNavigationCompleted;
+    public void UnregisterEvents()
+    {
+        if (_webView != null)
+        {
+            _webView.NavigationCompleted -= OnWebViewNavigationCompleted;
+        }
+    }
 
     private void OnWebViewNavigationCompleted(WebView2 sender, CoreWebView2NavigationCompletedEventArgs args) => NavigationCompleted?.Invoke(this, args.WebErrorStatus);
 }

code/TemplateStudioForWinUICs/Templates/Pg/WebView/ViewModels/Param_ItemNameViewModel.cs

@@ -12,15 +12,9 @@ namespace Param_RootNamespace.ViewModels;
 public class Param_ItemNameViewModel : System.ComponentModel.INotifyPropertyChanged, INavigationAware
 {
     // TODO: Set the default URL to display.
-    private const string DefaultUrl = "https://docs.microsoft.com/windows/apps/";
-    private Uri _source;
+    private Uri _source = new("https://docs.microsoft.com/windows/apps/");
     private bool _isLoading = true;
     private bool _hasFailures;
-    private ICommand _browserBackCommand;
-    private ICommand _browserForwardCommand;
-    private ICommand _openInBrowserCommand;
-    private ICommand _reloadCommand;
-    private ICommand _retryCommand;
 
     public IWebViewService WebViewService
     {
@@ -45,30 +39,45 @@ public class Param_ItemNameViewModel : System.ComponentModel.INotifyPropertyChan
         set => SetProperty(ref _hasFailures, value);
     }
 
-    public ICommand BrowserBackCommand => _browserBackCommand ??=
-        new RelayCommand(() => WebViewService?.GoBack(), () => WebViewService?.CanGoBack ?? false);
+    public ICommand BrowserBackCommand
+    {
+        get;
+    }
 
-    public ICommand BrowserForwardCommand => _browserForwardCommand ??=
-        new RelayCommand(() => WebViewService?.GoForward(), () => WebViewService?.CanGoForward ?? false);
+    public ICommand BrowserForwardCommand
+    {
+        get;
+    }
 
-    public ICommand ReloadCommand => _reloadCommand ??=
-        new RelayCommand(() => WebViewService?.Reload());
+    public ICommand ReloadCommand
+    {
+        get;
+    }
 
-    public ICommand RetryCommand => _retryCommand ??=
-        new RelayCommand(OnRetry);
+    public ICommand RetryCommand
+    {
+        get;
+    }
 
-    public ICommand OpenInBrowserCommand => _openInBrowserCommand ??=
-        new RelayCommand(async () => await Windows.System.Launcher.LaunchUriAsync(Source));
+    public ICommand OpenInBrowserCommand
+    {
+        get;
+    }
 
     public Param_ItemNameViewModel(IWebViewService webViewService)
     {
         WebViewService = webViewService;
+
+        BrowserBackCommand = new RelayCommand(() => WebViewService.GoBack(), () => WebViewService.CanGoBack);
+        BrowserForwardCommand = new RelayCommand(() => WebViewService.GoForward(), () => WebViewService.CanGoForward);
+        ReloadCommand = new RelayCommand(() => WebViewService.Reload());
+        RetryCommand = new RelayCommand(OnRetry);
+        OpenInBrowserCommand = new RelayCommand(async () => await Windows.System.Launcher.LaunchUriAsync(WebViewService.Source), () => WebViewService.Source != null);
     }
 
     public void OnNavigatedTo(object parameter)
     {
         WebViewService.NavigationCompleted += OnNavigationCompleted;
-        Source = new Uri(DefaultUrl);
     }
 
     public void OnNavigatedFrom()
@@ -77,7 +86,7 @@ public class Param_ItemNameViewModel : System.ComponentModel.INotifyPropertyChan
         WebViewService.NavigationCompleted -= OnNavigationCompleted;
     }
 
-    private void OnNavigationCompleted(object sender, CoreWebView2WebErrorStatus webErrorStatus)
+    private void OnNavigationCompleted(object? sender, CoreWebView2WebErrorStatus webErrorStatus)
     {
         IsLoading = false;
         OnPropertyChanged(nameof(BrowserBackCommand));

code/TemplateStudioForWinUICs/Templates/Pg/WebView/Views/Param_ItemNamePage.xaml.cs

@@ -13,7 +13,7 @@ public sealed partial class Param_ItemNamePage : Page
 
     public Param_ItemNamePage()
     {
-        ViewModel = App.GetService<Param_ItemNameViewModel>();
+        ViewModel = App.GetService<Param_ItemNameViewModel>()!;
         InitializeComponent();
 
         ViewModel.WebViewService.Initialize(WebView);

code/TemplateStudioForWinUICs/Templates/Proj/Default/Param_ProjectName/Param_ProjectName.csproj

@@ -1,5 +1,4 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
     <TargetFramework>net6.0-windows10.0.19041.0</TargetFramework>
@@ -9,8 +8,9 @@
     <Platforms>x86;x64;arm64</Platforms>
     <RuntimeIdentifiers>win10-x86;win10-x64;win10-arm64</RuntimeIdentifiers>
     <PublishProfile>Properties\PublishProfiles\win10-$(Platform).pubxml</PublishProfile>
-    <ImplicitUsings>enable</ImplicitUsings>
-    <UseWinUI>true</UseWinUI>
+	<ImplicitUsings>enable</ImplicitUsings>
+	<Nullable>enable</Nullable>
+	<UseWinUI>true</UseWinUI>
     <EnableMsixTooling>true</EnableMsixTooling>
     <WindowsPackageType>None</WindowsPackageType>
   </PropertyGroup>

code/TemplateStudioForWinUICs/Templates/_comp/MT/Page.AddBackCommand/ViewModels/Param_ItemNameDetailViewModel_postaction.cs

@@ -12,17 +12,24 @@ public class Param_ItemNameDetailViewModel : ObservableRecipient, INavigationAwa
 //{[{
     private readonly INavigationService _navigationService;
 //}]}
+
 //^^
 //{[{
-    private ICommand _goBackCommand;
+    public ICommand GoBackCommand
+    {
+        get;
+    }
 
-    public ICommand GoBackCommand => _goBackCommand ??= new RelayCommand(OnGoBack);
 //}]}
-
     public Param_ItemNameDetailViewModel(/*{[{*/INavigationService navigationService/*}]}*/)
     {
 //{[{
         _navigationService = navigationService;
+//}]}
+//^^
+//{[{
+
+        GoBackCommand = new RelayCommand(OnGoBack);
 //}]}
     }
 

code/TemplateStudioForWinUICs/Templates/_comp/MT/Page.AddViewModel/Views/Param_ItemNamePage_postaction.xaml.cs

@@ -16,7 +16,7 @@ public sealed partial class Param_ItemNamePage : Page
     public Param_ItemNamePage()
     {
 //{[{
-        ViewModel = App.GetService<Param_ItemNameViewModel>();
+        ViewModel = App.GetService<Param_ItemNameViewModel>()!;
 //}]}
     }
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Page.AddViewModelDetail/Views/Param_ItemNameDetailPage_postaction.xaml.cs

@@ -16,7 +16,7 @@ public sealed partial class Param_ItemNameDetailPage : Page
     public Param_ItemNameDetailPage()
     {
 //{[{
-        ViewModel = App.GetService<Param_ItemNameDetailViewModel>();
+        ViewModel = App.GetService<Param_ItemNameDetailViewModel>()!;
 //}]}
     }
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Page.Settings.Unpackaged/ViewModels/Param_ItemNameViewModel_postaction.cs

@@ -8,6 +8,6 @@ using System.Reflection;
         var appName = "AppDisplayName".GetLocalized();
         var version = Assembly.GetExecutingAssembly().GetName().Version;
 
-        return $"{appName} - {version.Major}.{version.Minor}.{version.Build}.{version.Revision}";
+        return $"{appName} - {version?.Major}.{version?.Minor}.{version?.Build}.{version?.Revision}";
         //}]}
     }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.MenuBar.AddMenuItem.Settings/ViewModels/ShellViewModel_postaction.cs

@@ -2,18 +2,30 @@
 
 public class ShellViewModel : ObservableRecipient
 {
-    private ICommand _menuFileExitCommand;
+    public ICommand MenuFileExitCommand
+    {
+        get;
+    }
 //{[{
-    private ICommand _menuParam_ItemNameCommand;
+    public ICommand MenuParam_ItemNameCommand
+    {
+        get;
+    }
 //}]}
-    public ICommand MenuFileExitCommand => _menuFileExitCommand ??= new RelayCommand(OnMenuFileExit);
-//{[{
+    public ShellViewModel(INavigationService navigationService)
+    {
+        NavigationService = navigationService;
+        NavigationService.Navigated += OnNavigated;
 
-    public ICommand MenuParam_ItemNameCommand => _menuParam_ItemNameCommand ??= new RelayCommand(OnMenuParam_ItemName);
+        MenuFileExitCommand = new RelayCommand(OnMenuFileExit);
+//{[{
+        MenuParam_ItemNameCommand = new RelayCommand(OnMenuParam_ItemName);
 //}]}
+    }
+
     private void OnMenuFileExit() => Application.Current.Exit();
 //{[{
 
-    private void OnMenuParam_ItemName() => NavigationService.NavigateTo(typeof(Param_ItemNameViewModel).FullName);
+    private void OnMenuParam_ItemName() => NavigationService.NavigateTo(typeof(Param_ItemNameViewModel).FullName!);
 //}]}
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.MenuBar.AddMenuItem/ViewModels/ShellViewModel_postaction.cs

@@ -2,18 +2,30 @@
 
 public class ShellViewModel : ObservableRecipient
 {
-    private ICommand _menuFileExitCommand;
+    public ICommand MenuFileExitCommand
+    {
+        get;
+    }
 //{[{
-    private ICommand _menuViewsParam_ItemNameCommand;
+    public ICommand MenuViewsParam_ItemNameCommand
+    {
+        get;
+    }
 //}]}
-    public ICommand MenuFileExitCommand => _menuFileExitCommand ??= new RelayCommand(OnMenuFileExit);
-//{[{
+    public ShellViewModel(INavigationService navigationService)
+    {
+        NavigationService = navigationService;
+        NavigationService.Navigated += OnNavigated;
 
-    public ICommand MenuViewsParam_ItemNameCommand => _menuViewsParam_ItemNameCommand ??= new RelayCommand(OnMenuViewsParam_ItemName);
+        MenuFileExitCommand = new RelayCommand(OnMenuFileExit);
+//{[{
+        MenuViewsParam_ItemNameCommand = new RelayCommand(OnMenuViewsParam_ItemName);
 //}]}
+    }
+
     private void OnMenuFileExit() => Application.Current.Exit();
 //{[{
 
-    private void OnMenuViewsParam_ItemName() => NavigationService.NavigateTo(typeof(Param_ItemNameViewModel).FullName);
+    private void OnMenuViewsParam_ItemName() => NavigationService.NavigateTo(typeof(Param_ItemNameViewModel).FullName!);
 //}]}
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.MenuBar/ViewModels/ShellViewModel.cs

@@ -11,10 +11,11 @@ namespace Param_RootNamespace.ViewModels;
 public class ShellViewModel : ObservableRecipient
 {
     private bool _isBackEnabled;
-    private object _selected;
-    private ICommand _menuFileExitCommand;
 
-    public ICommand MenuFileExitCommand => _menuFileExitCommand ??= new RelayCommand(OnMenuFileExit);
+    public ICommand MenuFileExitCommand
+    {
+        get;
+    }
 
     public INavigationService NavigationService
     {
@@ -27,16 +28,12 @@ public class ShellViewModel : ObservableRecipient
         set => SetProperty(ref _isBackEnabled, value);
     }
 
-    public object Selected
-    {
-        get => _selected;
-        set => SetProperty(ref _selected, value);
-    }
-
     public ShellViewModel(INavigationService navigationService)
     {
         NavigationService = navigationService;
         NavigationService.Navigated += OnNavigated;
+
+        MenuFileExitCommand = new RelayCommand(OnMenuFileExit);
     }
 
     private void OnNavigated(object sender, NavigationEventArgs e) => IsBackEnabled = NavigationService.CanGoBack;

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.MenuBar/Views/ShellPage.xaml.cs

@@ -67,7 +67,7 @@ public sealed partial class ShellPage : Page
 
     private static void OnKeyboardAcceleratorInvoked(KeyboardAccelerator sender, KeyboardAcceleratorInvokedEventArgs args)
     {
-        var navigationService = App.GetService<INavigationService>();
+        var navigationService = App.GetService<INavigationService>()!;
 
         var result = navigationService.GoBack();
 

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView.AddNavViewItem.Settings/Services/NavigationViewService_postaction.cs

@@ -11,7 +11,7 @@ public class NavigationViewService : INavigationViewService
             // Navigate to the settings page.
 //}--}
 //{[{
-            _navigationService.NavigateTo(typeof(Param_ItemNameViewModel).FullName);
+            _navigationService.NavigateTo(typeof(Param_ItemNameViewModel).FullName!);
 //}]}
         }
     }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView/Behaviors/NavigationViewHeaderBehavior.cs

@@ -8,11 +8,11 @@ namespace Param_RootNamespace.Behaviors;
 
 public class NavigationViewHeaderBehavior : Behavior<NavigationView>
 {
-    private static NavigationViewHeaderBehavior _current;
+    private static NavigationViewHeaderBehavior? _current;
 
-    private Page _currentPage;
+    private Page? _currentPage;
 
-    public DataTemplate DefaultHeaderTemplate
+    public DataTemplate? DefaultHeaderTemplate
     {
         get; set;
     }
@@ -24,48 +24,50 @@ public class NavigationViewHeaderBehavior : Behavior<NavigationView>
     }
 
     public static readonly DependencyProperty DefaultHeaderProperty =
-        DependencyProperty.Register("DefaultHeader", typeof(object), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(null, (d, e) => _current.UpdateHeader()));
+        DependencyProperty.Register("DefaultHeader", typeof(object), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(null, (d, e) => _current!.UpdateHeader()));
 
     public static NavigationViewHeaderMode GetHeaderMode(Page item) => (NavigationViewHeaderMode)item.GetValue(HeaderModeProperty);
 
     public static void SetHeaderMode(Page item, NavigationViewHeaderMode value) => item.SetValue(HeaderModeProperty, value);
 
     public static readonly DependencyProperty HeaderModeProperty =
-        DependencyProperty.RegisterAttached("HeaderMode", typeof(bool), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(NavigationViewHeaderMode.Always, (d, e) => _current.UpdateHeader()));
+        DependencyProperty.RegisterAttached("HeaderMode", typeof(bool), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(NavigationViewHeaderMode.Always, (d, e) => _current!.UpdateHeader()));
 
     public static object GetHeaderContext(Page item) => item.GetValue(HeaderContextProperty);
 
     public static void SetHeaderContext(Page item, object value) => item.SetValue(HeaderContextProperty, value);
 
     public static readonly DependencyProperty HeaderContextProperty =
-        DependencyProperty.RegisterAttached("HeaderContext", typeof(object), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(null, (d, e) => _current.UpdateHeader()));
+        DependencyProperty.RegisterAttached("HeaderContext", typeof(object), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(null, (d, e) => _current!.UpdateHeader()));
 
     public static DataTemplate GetHeaderTemplate(Page item) => (DataTemplate)item.GetValue(HeaderTemplateProperty);
 
     public static void SetHeaderTemplate(Page item, DataTemplate value) => item.SetValue(HeaderTemplateProperty, value);
 
     public static readonly DependencyProperty HeaderTemplateProperty =
-        DependencyProperty.RegisterAttached("HeaderTemplate", typeof(DataTemplate), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(null, (d, e) => _current.UpdateHeaderTemplate()));
+        DependencyProperty.RegisterAttached("HeaderTemplate", typeof(DataTemplate), typeof(NavigationViewHeaderBehavior), new PropertyMetadata(null, (d, e) => _current!.UpdateHeaderTemplate()));
 
     protected override void OnAttached()
     {
         base.OnAttached();
-        _current = this;
-        var navigationService = App.GetService<INavigationService>();
+
+        var navigationService = App.GetService<INavigationService>()!;
         navigationService.Navigated += OnNavigated;
+
+        _current = this;
     }
 
     protected override void OnDetaching()
     {
         base.OnDetaching();
-        var navigationService = App.GetService<INavigationService>();
+
+        var navigationService = App.GetService<INavigationService>()!;
         navigationService.Navigated -= OnNavigated;
     }
 
     private void OnNavigated(object sender, NavigationEventArgs e)
     {
-        var frame = sender as Frame;
-        if (frame.Content is Page page)
+        if (sender is Frame frame && frame.Content is Page page)
         {
             _currentPage = page;
 

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView/Contracts/Services/INavigationViewService.cs

@@ -4,12 +4,12 @@ namespace Param_RootNamespace.Contracts.Services;
 
 public interface INavigationViewService
 {
-    IList<object> MenuItems
+    IList<object>? MenuItems
     {
         get;
     }
 
-    object SettingsItem
+    object? SettingsItem
     {
         get;
     }
@@ -18,5 +18,5 @@ public interface INavigationViewService
 
     void UnregisterEvents();
 
-    NavigationViewItem GetSelectedItem(Type pageType);
+    NavigationViewItem? GetSelectedItem(Type pageType);
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView/Services/ActivationService_postaction.cs

@@ -7,7 +7,7 @@ public class ActivationService : IActivationService
         if (App.MainWindow.Content == null)
         {
 //{[{
-            _shell = App.GetService<ShellPage>();
+            _shell = App.GetService<ShellPage>()!;
 //}]}
         }
     }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView/Services/NavigationViewService.cs

@@ -1,4 +1,5 @@
-using Microsoft.UI.Xaml.Controls;
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.UI.Xaml.Controls;
 using Param_RootNamespace.Contracts.Services;
 using Param_RootNamespace.Helpers;
 using Param_RootNamespace.ViewModels;
@@ -11,11 +12,11 @@ public class NavigationViewService : INavigationViewService
 
     private readonly IPageService _pageService;
 
-    private NavigationView _navigationView;
+    private NavigationView? _navigationView;
 
-    public IList<object> MenuItems => _navigationView.MenuItems;
+    public IList<object>? MenuItems => _navigationView?.MenuItems;
 
-    public object SettingsItem => _navigationView.SettingsItem;
+    public object? SettingsItem => _navigationView?.SettingsItem;
 
     public NavigationViewService(INavigationService navigationService, IPageService pageService)
     {
@@ -23,6 +24,7 @@ public class NavigationViewService : INavigationViewService
         _pageService = pageService;
     }
 
+    [MemberNotNull(nameof(_navigationView))]
     public void Initialize(NavigationView navigationView)
     {
         _navigationView = navigationView;
@@ -32,11 +34,22 @@ public class NavigationViewService : INavigationViewService
 
     public void UnregisterEvents()
     {
-        _navigationView.BackRequested -= OnBackRequested;
-        _navigationView.ItemInvoked -= OnItemInvoked;
+        if (_navigationView != null)
+        {
+            _navigationView.BackRequested -= OnBackRequested;
+            _navigationView.ItemInvoked -= OnItemInvoked;
+        }
     }
 
-    public NavigationViewItem GetSelectedItem(Type pageType) => GetSelectedItem(_navigationView.MenuItems, pageType);
+    public NavigationViewItem? GetSelectedItem(Type pageType)
+    {
+        if (_navigationView != null)
+        {
+            return GetSelectedItem(_navigationView.MenuItems, pageType);
+        }
+
+        return null;
+    }
 
     private void OnBackRequested(NavigationView sender, NavigationViewBackRequestedEventArgs args) => _navigationService.GoBack();
 
@@ -50,14 +63,14 @@ public class NavigationViewService : INavigationViewService
         {
             var selectedItem = args.InvokedItemContainer as NavigationViewItem;
 
-            if (selectedItem.GetValue(NavigationHelper.NavigateToProperty) is string pageKey)
+            if (selectedItem?.GetValue(NavigationHelper.NavigateToProperty) is string pageKey)
             {
                 _navigationService.NavigateTo(pageKey);
             }
         }
     }
 
-    private NavigationViewItem GetSelectedItem(IEnumerable<object> menuItems, Type pageType)
+    private NavigationViewItem? GetSelectedItem(IEnumerable<object> menuItems, Type pageType)
     {
         foreach (var item in menuItems.OfType<NavigationViewItem>())
         {

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView/ViewModels/ShellViewModel.cs

@@ -9,7 +9,7 @@ namespace Param_RootNamespace.ViewModels;
 public class ShellViewModel : ObservableRecipient
 {
     private bool _isBackEnabled;
-    private object _selected;
+    private object? _selected;
 
     public INavigationService NavigationService
     {
@@ -27,7 +27,7 @@ public class ShellViewModel : ObservableRecipient
         set => SetProperty(ref _isBackEnabled, value);
     }
 
-    public object Selected
+    public object? Selected
     {
         get => _selected;
         set => SetProperty(ref _selected, value);

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project.NavView/Views/ShellPage.xaml.cs

@@ -76,7 +76,7 @@ public sealed partial class ShellPage : Page
 
     private static void OnKeyboardAcceleratorInvoked(KeyboardAccelerator sender, KeyboardAcceleratorInvokedEventArgs args)
     {
-        var navigationService = App.GetService<INavigationService>();
+        var navigationService = App.GetService<INavigationService>()!;
 
         var result = navigationService.GoBack();
 

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Activation/ActivationHandler.cs

@@ -11,7 +11,7 @@ public abstract class ActivationHandler<T> : IActivationHandler
     // Override this method to add the logic for your activation handler.
     protected abstract Task HandleInternalAsync(T args);
 
-    public bool CanHandle(object args) => args is T && CanHandleInternal(args as T);
+    public bool CanHandle(object args) => args is T && CanHandleInternal((args as T)!);
 
-    public async Task HandleAsync(object args) => await HandleInternalAsync(args as T);
+    public async Task HandleAsync(object args) => await HandleInternalAsync((args as T)!);
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Activation/DefaultActivationHandler.cs

@@ -16,12 +16,12 @@ public class DefaultActivationHandler : ActivationHandler<LaunchActivatedEventAr
     protected override bool CanHandleInternal(LaunchActivatedEventArgs args)
     {
         // None of the ActivationHandlers has handled the activation.
-        return _navigationService.Frame.Content == null;
+        return _navigationService.Frame?.Content == null;
     }
 
     protected async override Task HandleInternalAsync(LaunchActivatedEventArgs args)
     {
-        _navigationService.NavigateTo(typeof(Param_HomeNameViewModel).FullName, args.Arguments);
+        _navigationService.NavigateTo(typeof(Param_HomeNameViewModel).FullName!, args.Arguments);
 
         await Task.CompletedTask;
     }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/App_postaction.xaml.cs

@@ -43,7 +43,7 @@ public partial class App : Application
         })
         .Build();
 
-    public static T GetService<T>()
+    public static T? GetService<T>()
         where T : class
     {
         return _host.Services.GetService(typeof(T)) as T;
@@ -54,7 +54,7 @@ public partial class App : Application
     {
 //^^
 //{[{
-        var activationService = App.GetService<IActivationService>();
+        var activationService = App.GetService<IActivationService>()!;
         await activationService.ActivateAsync(args);
 //}]}
     }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Contracts/Services/INavigationService.cs

@@ -12,12 +12,12 @@ public interface INavigationService
         get;
     }
 
-    Frame Frame
+    Frame? Frame
     {
         get; set;
     }
 
-    bool NavigateTo(string pageKey, object parameter = null, bool clearNavigation = false);
+    bool NavigateTo(string pageKey, object? parameter = null, bool clearNavigation = false);
 
     bool GoBack();
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Helpers/FrameExtensions.cs

@@ -4,5 +4,5 @@ namespace Param_RootNamespace.Helpers;
 
 public static class FrameExtensions
 {
-    public static object GetPageViewModel(this Frame frame) => frame?.Content?.GetType().GetProperty("ViewModel")?.GetValue(frame.Content, null);
+    public static object? GetPageViewModel(this Frame frame) => frame?.Content?.GetType().GetProperty("ViewModel")?.GetValue(frame.Content, null);
 }

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Services/ActivationService.cs

@@ -10,7 +10,7 @@ public class ActivationService : IActivationService
 {
     private readonly ActivationHandler<LaunchActivatedEventArgs> _defaultHandler;
     private readonly IEnumerable<IActivationHandler> _activationHandlers;
-    private UIElement _shell = null;
+    private UIElement? _shell = null;
 
     public ActivationService(ActivationHandler<LaunchActivatedEventArgs> defaultHandler, IEnumerable<IActivationHandler> activationHandlers)
     {

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Services/NavigationService.cs

@@ -1,4 +1,5 @@
-using Microsoft.UI.Xaml.Controls;
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Navigation;
 using Param_RootNamespace.Contracts.Services;
 using Param_RootNamespace.Contracts.ViewModels;
@@ -11,12 +12,12 @@ namespace Param_RootNamespace.Services;
 public class NavigationService : INavigationService
 {
     private readonly IPageService _pageService;
-    private object _lastParameterUsed;
-    private Frame _frame;
+    private object? _lastParameterUsed;
+    private Frame? _frame;
 
-    public event NavigatedEventHandler Navigated;
+    public event NavigatedEventHandler? Navigated;
 
-    public Frame Frame
+    public Frame? Frame
     {
         get
         {
@@ -37,7 +38,8 @@ public class NavigationService : INavigationService
         }
     }
 
-    public bool CanGoBack => Frame.CanGoBack;
+    [MemberNotNullWhen(true, nameof(Frame), nameof(_frame))]
+    public bool CanGoBack => Frame != null && Frame.CanGoBack;
 
     public NavigationService(IPageService pageService)
     {
@@ -77,11 +79,11 @@ public class NavigationService : INavigationService
         return false;
     }
 
-    public bool NavigateTo(string pageKey, object parameter = null, bool clearNavigation = false)
+    public bool NavigateTo(string pageKey, object? parameter = null, bool clearNavigation = false)
     {
         var pageType = _pageService.GetPageType(pageKey);
 
-        if (_frame.Content?.GetType() != pageType || (parameter != null && !parameter.Equals(_lastParameterUsed)))
+        if (_frame != null && (_frame.Content?.GetType() != pageType || (parameter != null && !parameter.Equals(_lastParameterUsed))))
         {
             _frame.Tag = clearNavigation;
             var vmBeforeNavigation = _frame.GetPageViewModel();

code/TemplateStudioForWinUICs/Templates/_comp/MT/Project/Services/PageService.cs

@@ -16,7 +16,7 @@ public class PageService : IPageService
 
     public Type GetPageType(string key)
     {
-        Type pageType;
+        Type? pageType;
         lock (_pages)
         {
             if (!_pages.TryGetValue(key, out pageType))
@@ -34,7 +34,7 @@ public class PageService : IPageService
     {
         lock (_pages)
         {
-            var key = typeof(VM).FullName;
+            var key = typeof(VM).FullName!;
             if (_pages.ContainsKey(key))
             {
                 throw new ArgumentException($"The key {key} is already configured in PageService");