Code Quality: Address all nullable and XAML compiler warnings

Directory.Build.props

@@ -9,6 +9,7 @@
     <WindowsSdkPackageVersion>10.0.26100.67-preview</WindowsSdkPackageVersion>
     <WindowsTargetFramework>$(TargetFrameworkVersion)-windows$(TargetWindowsVersion)</WindowsTargetFramework>
     <LangVersion>preview</LangVersion>
+    <WarningsAsErrors>nullable</WarningsAsErrors>
 
     <!--  Use Microsoft.Testing.Platform  -->
     <EnableMSTestRunner>true</EnableMSTestRunner>

src/Files.App.Controls/Omnibar/IOmnibarTextMemberPathProvider.cs

@@ -15,6 +15,6 @@ public interface IOmnibarTextMemberPathProvider
 		/// Retrieves the path of the text member as a string. This path can be used to identify the location of the text member.
 		/// </summary>
 		/// <returns>Returns a string representing the path of the text member.</returns>
-		string GetTextMemberPath(string textMemberPath);
+		string? GetTextMemberPath(string textMemberPath);
 	}
 }

src/Files.App.Controls/Omnibar/Omnibar.cs

@@ -275,7 +275,7 @@ private string GetObjectText(object obj)
 			return obj is string text
 				? text
 				: obj is IOmnibarTextMemberPathProvider textMemberPathProvider
-					? textMemberPathProvider.GetTextMemberPath(CurrentSelectedMode.TextMemberPath ?? string.Empty)
+					? textMemberPathProvider.GetTextMemberPath(CurrentSelectedMode.TextMemberPath ?? string.Empty) ?? string.Empty
 					: obj.ToString() ?? string.Empty;
 		}
 

src/Files.App.Controls/Sidebar/ISidebarItemModel.cs

@@ -1,10 +1,24 @@
 // Copyright (c) Files Community
 // Licensed under the MIT License.
 
+using Microsoft.UI.Xaml;
+
 namespace Files.App.Controls
 {
+	public interface ISidebarItemPresentationModel
+	{
+		string? Text { get; }
+
+		object? ToolTip { get; }
+
+		FrameworkElement? IconElement { get; }
+
+		FrameworkElement? ItemDecorator { get; }
+	}
+
 	public interface ISidebarItemModel : INotifyPropertyChanged
 	{
+
 		/// <summary>
 		/// The children of this item that will be rendered as child elements of the SidebarItem
 		/// </summary>

src/Files.App.Controls/Sidebar/SidebarItem.Properties.cs

@@ -83,7 +83,15 @@ public ISidebarItemModel? Item
 			set { SetValue(ItemProperty, value); }
 		}
 		public static readonly DependencyProperty ItemProperty =
-			DependencyProperty.Register(nameof(Item), typeof(ISidebarItemModel), typeof(SidebarItem), new PropertyMetadata(null));
+			DependencyProperty.Register(nameof(Item), typeof(ISidebarItemModel), typeof(SidebarItem), new PropertyMetadata(null, OnPropertyChanged));
+
+		public bool UseItemPresentation
+		{
+			get { return (bool)GetValue(UseItemPresentationProperty); }
+			set { SetValue(UseItemPresentationProperty, value); }
+		}
+		public static readonly DependencyProperty UseItemPresentationProperty =
+			DependencyProperty.Register(nameof(UseItemPresentation), typeof(bool), typeof(SidebarItem), new PropertyMetadata(false, OnPropertyChanged));
 
 		public bool UseReorderDrop
 		{
@@ -136,12 +144,18 @@ public static void OnPropertyChanged(DependencyObject sender, DependencyProperty
 			}
 			else if (e.Property == IsExpandedProperty)
 			{
+				if (item.UseItemPresentation && item.Item is { } model && model.IsExpanded != item.IsExpanded)
+					model.IsExpanded = item.IsExpanded;
 				item.UpdateExpansionState();
 			}
 			else if (e.Property == ItemProperty)
 			{
 				item.HandleItemChange();
 			}
+			else if (e.Property == UseItemPresentationProperty && item.UseItemPresentation)
+			{
+				item.UpdateItemPresentation();
+			}
 			else
 			{
 				Debug.Write(e.Property.ToString());

src/Files.App.Controls/Sidebar/SidebarItem.cs

@@ -90,7 +90,10 @@ protected override void OnApplyTemplate()
 				if (GetTemplateChild("ChevronContainer") is Border chevronContainer)
 					chevronContainer.PointerPressed += ChevronContainer_PointerPressed;
 				if (GetTemplateChild("FlyoutChildrenPresenter") is ItemsRepeater flyoutRepeater)
+				{
 					flyoutRepeater.ElementPrepared += FlyoutChildrenPresenter_ElementPrepared;
+					flyoutRepeater.ItemsSource = Item?.Children;
+				}
 			}
 
 			if (Owner is null)
@@ -124,11 +127,31 @@ private void SidebarItem_Loaded(object sender, RoutedEventArgs e)
 		public void HandleItemChange()
 		{
 			HookupItemChangeListener(null, Item);
+			if (UseItemPresentation)
+				UpdateItemPresentation();
+			UpdateFlyoutChildrenSource();
 			UpdateExpansionState();
 			ReevaluateSelection();
 			CanDrag = Item?.Path is string path && Path.IsPathRooted(path);
 		}
 
+		private void UpdateItemPresentation()
+		{
+			var presentation = Item as ISidebarItemPresentationModel;
+			AutomationProperties.SetAutomationId(this, presentation?.Text ?? string.Empty);
+			Text = presentation?.Text;
+			ToolTip = presentation?.ToolTip;
+			Icon = presentation?.IconElement;
+			Decorator = presentation?.ItemDecorator;
+			IsExpanded = Item?.IsExpanded ?? true;
+		}
+
+		private void UpdateFlyoutChildrenSource()
+		{
+			if (GetTemplateChild("FlyoutChildrenPresenter") is ItemsRepeater flyoutRepeater)
+				flyoutRepeater.ItemsSource = Item?.Children;
+		}
+
 		private void HookupOwners()
 		{
 			// Owner is pushed in by the hosting SidebarView's MenuItemsHost_ElementPrepared (top-level rows) or the parent SidebarItem's FlyoutChildrenPresenter_ElementPrepared (flyout children) before Loaded fires. Static SidebarItems declared directly in XAML (MainPage's SettingsButton in SidebarView.Footer) aren't realized through either path, so resolve Owner via a visual-tree walk for them. OwnerExpansionSupport state is applied by OnOwnerChanged.
@@ -181,9 +204,46 @@ private void Item_PropertyChanged(object? sender, PropertyChangedEventArgs e)
 		{
 			switch (e.PropertyName)
 			{
+				case null:
+				case "":
+					if (UseItemPresentation)
+						UpdateItemPresentation();
+					UpdateFlyoutChildrenSource();
+					UpdateExpansionState();
+					ReevaluateSelection();
+					break;
+				case nameof(ISidebarItemPresentationModel.Text):
+					if (UseItemPresentation)
+					{
+						var presentation = Item as ISidebarItemPresentationModel;
+						Text = presentation?.Text;
+						AutomationProperties.SetAutomationId(this, presentation?.Text ?? string.Empty);
+					}
+					break;
+				case nameof(ISidebarItemPresentationModel.ToolTip):
+					if (UseItemPresentation)
+						ToolTip = (Item as ISidebarItemPresentationModel)?.ToolTip;
+					break;
+				case nameof(ISidebarItemPresentationModel.IconElement):
+					if (UseItemPresentation)
+						Icon = (Item as ISidebarItemPresentationModel)?.IconElement;
+					break;
+				case nameof(ISidebarItemPresentationModel.ItemDecorator):
+					if (UseItemPresentation)
+						Decorator = (Item as ISidebarItemPresentationModel)?.ItemDecorator;
+					break;
+				case nameof(ISidebarItemModel.IsExpanded):
+					if (UseItemPresentation)
+						IsExpanded = Item?.IsExpanded ?? true;
+					UpdateExpansionState();
+					break;
 				case nameof(ISidebarItemModel.HasUnrealizedChildren):
 				case nameof(ISidebarItemModel.IsLeafWithChildren):
+					UpdateExpansionState();
+					ReevaluateSelection();
+					break;
 				case nameof(ISidebarItemModel.Children):
+					UpdateFlyoutChildrenSource();
 					UpdateExpansionState();
 					ReevaluateSelection();
 					break;

src/Files.App.Controls/Sidebar/SidebarStyles.xaml

@@ -36,20 +36,6 @@
 		<Setter Target="Padding" Value="0" />
 	</Style>
 
-	<DataTemplate x:Key="DefaultSidebarItemTemplate">
-		<local:SidebarItem
-			AutomationProperties.AutomationId="{Binding Item.Text}"
-			ContentOpacity="{Binding RowOpacity}"
-			Decorator="{Binding Item.ItemDecorator}"
-			Icon="{Binding Item.IconElement}"
-			IsExpanded="{Binding Item.IsExpanded, Mode=TwoWay}"
-			Item="{Binding Item}"
-			Margin="{Binding SectionGapMargin}"
-			NestingLevel="{Binding Depth}"
-			Text="{Binding Item.Text}"
-			ToolTip="{Binding Item.ToolTip}" />
-	</DataTemplate>
-
 	<Style TargetType="local:SidebarItem">
 		<Setter Property="IsTabStop" Value="False" />
 		<Setter Property="Template">
@@ -211,19 +197,13 @@
 											x:Name="FlyoutChildrenPresenter"
 											HorizontalAlignment="Stretch"
 											AutomationProperties.AccessibilityView="Content"
-											ItemsSource="{Binding Item.Children, Mode=OneWay}"
 											XYFocusKeyboardNavigation="Enabled">
 											<ItemsRepeater.ItemTemplate>
 												<DataTemplate>
 													<local:SidebarItem
-														AutomationProperties.AutomationId="{Binding Text}"
-														Decorator="{Binding ItemDecorator}"
-														Icon="{Binding IconElement}"
-														IsExpanded="{Binding IsExpanded, Mode=TwoWay}"
 														IsInFlyout="True"
 														Item="{Binding}"
-														Text="{Binding Text}"
-														ToolTip="{Binding ToolTip}" />
+														UseItemPresentation="True" />
 												</DataTemplate>
 											</ItemsRepeater.ItemTemplate>
 										</ItemsRepeater>

src/Files.App.Controls/Sidebar/SidebarView.xaml

@@ -4,12 +4,27 @@
 	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 	xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+	xmlns:local="using:Files.App.Controls"
 	xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
 	HorizontalAlignment="Stretch"
 	Loaded="SidebarView_Loaded"
 	TabFocusNavigation="Local"
 	mc:Ignorable="d">
 
+	<UserControl.Resources>
+		<DataTemplate
+			x:Key="DefaultSidebarItemTemplate"
+			x:DataType="local:FlatSidebarItem">
+			<local:SidebarItem
+				ContentOpacity="{x:Bind RowOpacity}"
+				DataContext="{x:Bind}"
+				Item="{x:Bind Item}"
+				Margin="{x:Bind SectionGapMargin, Mode=OneWay}"
+				NestingLevel="{x:Bind Depth}"
+				UseItemPresentation="True" />
+		</DataTemplate>
+	</UserControl.Resources>
+
 	<Grid>
 		<Grid.ColumnDefinitions>
 			<ColumnDefinition

src/Files.App.Launcher/Files.App.Launcher.vcxproj

@@ -45,7 +45,7 @@
   <PropertyGroup Condition="'$(Configuration)'!='Debug'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
-    <PlatformToolset>v143</PlatformToolset>
+    <PlatformToolset>v145</PlatformToolset>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
     <LinkIncremental>false</LinkIncremental>

src/Files.App/Actions/Content/Archives/Compress/BaseCompressArchiveAction.cs

@@ -37,21 +37,29 @@ public BaseCompressArchiveAction()
 
 		protected void GetDestination(out string[] sources, out string directory, out string fileName)
 		{
-			sources = context.SelectedItems.Select(item => item.ItemPath).ToArray();
+			sources = context.SelectedItems
+				.Select(item => item.GetRequiredPath())
+				.ToArray();
 			directory = string.Empty;
 			fileName = string.Empty;
 
 			if (sources.Length is not 0)
 			{
 				// Get the current directory path
-				directory = context.ShellPage.ShellViewModel.WorkingDirectory.Normalize();
+				var shellPage = context.ShellPage ?? throw new InvalidOperationException("An active shell page is required to compress items.");
+				var shellViewModel = shellPage.GetRequiredShellViewModel();
+				var workingDirectory = shellViewModel.WorkingDirectory
+					?? throw new InvalidOperationException("The active shell page does not have a working directory.");
+				directory = workingDirectory.Normalize();
 
 				// Get the library save folder if the folder is library item
 				if (App.LibraryManager.TryGetLibrary(directory, out var library) && !library.IsEmpty)
-					directory = library.DefaultSaveFolder;
+					directory = library.DefaultSaveFolder
+						?? throw new InvalidOperationException("The library does not have a default save folder.");
 
 				// Gets the file name from the directory path
-				fileName = SystemIO.Path.GetFileName(sources.Length is 1 ? sources[0] : directory);
+				fileName = SystemIO.Path.GetFileName(sources.Length is 1 ? sources[0] : directory)
+					?? throw new InvalidOperationException("The archive destination does not have a file name.");
 			}
 		}
 

src/Files.App/Actions/Content/Archives/Decompress/BaseDecompressArchiveAction.cs

@@ -56,13 +56,13 @@ protected async Task DecompressArchiveHereAsync(bool smart = false)
 				return;
 
 			var selectedItems = context.SelectedItems.ToList();
-			var currentFolderPath = context.ShellPage?.ShellViewModel.CurrentFolder?.ItemPath ?? string.Empty;
-			BaseStorageFolder currentFolder = await StorageHelpers.ToStorageItem<BaseStorageFolder>(currentFolderPath);
+			var currentFolderPath = context.ShellPage?.ShellViewModel!.CurrentFolder?.ItemPath ?? string.Empty;
+			BaseStorageFolder? currentFolder = await StorageHelpers.ToStorageItem<BaseStorageFolder>(currentFolderPath);
 
 			foreach (var selectedItem in selectedItems)
 			{
 				var password = string.Empty;
-				BaseStorageFile archive = await StorageHelpers.ToStorageItem<BaseStorageFile>(selectedItem.ItemPath);
+				BaseStorageFile? archive = await StorageHelpers.ToStorageItem<BaseStorageFile>(selectedItem.ItemPath!);
 
 				if (archive?.Path is null)
 					return;
@@ -140,7 +140,7 @@ static ReadOnlySpan<char> GetFirstMeaningfulSegment(ReadOnlySpan<char> path)
 				if (smart && currentFolder is not null && isMultipleItems)
 				{
 					destinationFolder =
-						await FilesystemTasks.Wrap(() =>
+						await FilesystemTasks.WrapNullable(() =>
 							currentFolder.CreateFolderAsync(
 								SystemIO.Path.GetFileNameWithoutExtension(archive.Path),
 								CreationCollisionOption.GenerateUniqueName).AsTask());
@@ -152,7 +152,7 @@ await FilesystemTasks.Wrap(() =>
 
 				// Operate decompress
 				var result = await FilesystemTasks.Wrap(() =>
-					StorageArchiveService.DecompressAsync(selectedItem.ItemPath, destinationFolder?.Path ?? string.Empty, password));
+					StorageArchiveService.DecompressAsync(selectedItem.ItemPath!, destinationFolder?.Path ?? string.Empty, password));
 			}
 		}
 

src/Files.App/Actions/Content/Archives/Decompress/DecompressArchive.cs

@@ -42,7 +42,7 @@ public override async Task ExecuteAsync(object? parameter = null)
 			if (string.IsNullOrEmpty(archivePath))
 				return;
 
-			BaseStorageFile archive = await StorageHelpers.ToStorageItem<BaseStorageFile>(archivePath);
+			BaseStorageFile? archive = await StorageHelpers.ToStorageItem<BaseStorageFile>(archivePath);
 
 			if (archive?.Path is null)
 				return;
@@ -83,21 +83,24 @@ public override async Task ExecuteAsync(object? parameter = null)
 			if (!StorageHelpers.Exists(archive.Path))
 				return;
 
-			BaseStorageFolder destinationFolder = decompressArchiveViewModel.DestinationFolder;
+			BaseStorageFolder? destinationFolder = decompressArchiveViewModel.DestinationFolder;
 			string destinationFolderPath = decompressArchiveViewModel.DestinationFolderPath;
 
 			// Save extraction location for future use
 			SaveExtractionLocation(destinationFolderPath);
 
 			if (destinationFolder is null)
 			{
-				BaseStorageFolder parentFolder = await StorageHelpers.ToStorageItem<BaseStorageFolder>(Path.GetDirectoryName(archive.Path) ?? string.Empty);
-				destinationFolder = await FilesystemTasks.Wrap(() => parentFolder.CreateFolderAsync(Path.GetFileName(destinationFolderPath), CreationCollisionOption.GenerateUniqueName).AsTask());
+				BaseStorageFolder? parentFolder = await StorageHelpers.ToStorageItem<BaseStorageFolder>(Path.GetDirectoryName(archive.Path) ?? string.Empty);
+				if (parentFolder is null)
+					throw new InvalidOperationException("The archive's parent folder could not be resolved.");
+
+				destinationFolder = await FilesystemTasks.WrapNullable(() => parentFolder.CreateFolderAsync(Path.GetFileName(destinationFolderPath), CreationCollisionOption.GenerateUniqueName).AsTask());
 			}
 
 			// Operate decompress
 			var result = await FilesystemTasks.Wrap(() =>
-				StorageArchiveService.DecompressAsync(archive?.Path ?? string.Empty, destinationFolder?.Path ?? string.Empty, password, encoding));
+				StorageArchiveService.DecompressAsync(archive.Path, destinationFolder?.Path ?? string.Empty, password, encoding));
 
 			if (decompressArchiveViewModel.OpenDestinationFolderOnCompletion)
 				await NavigationHelpers.OpenPath(destinationFolderPath, context.ShellPage, FilesystemItemType.Directory);