Fix item idx not being returned

src/modules/peek/Peek.FilePreviewer/FilePreview.xaml.cs

@@ -6,11 +6,11 @@ namespace Peek.FilePreviewer
 {
     using System;
     using System.Text;
+    using System.Threading;
     using System.Threading.Tasks;
     using CommunityToolkit.Mvvm.ComponentModel;
     using Microsoft.UI.Xaml;
     using Microsoft.UI.Xaml.Controls;
-    using Microsoft.UI.Xaml.Media.Imaging;
     using Peek.Common.Helpers;
     using Peek.Common.Models;
     using Peek.FilePreviewer.Models;
@@ -42,6 +42,8 @@ namespace Peek.FilePreviewer
         [ObservableProperty]
         private string imageInfoTooltip = ResourceLoader.GetForViewIndependentUse().GetString("PreviewTooltip_Blank");
 
+        private CancellationTokenSource _cancellationTokenSource = new ();
+
         public FilePreview()
         {
             InitializeComponent();
@@ -54,8 +56,12 @@ namespace Peek.FilePreviewer
             {
                 if (Previewer?.State == PreviewState.Error)
                 {
+                    // Cancel previous loading task
+                    _cancellationTokenSource.Cancel();
+                    _cancellationTokenSource = new ();
+
                     Previewer = previewerFactory.CreateDefaultPreviewer(File);
-                    await UpdatePreviewAsync();
+                    await UpdatePreviewAsync(_cancellationTokenSource.Token);
                 }
             }
         }
@@ -89,6 +95,10 @@ namespace Peek.FilePreviewer
 
         private async Task OnFilePropertyChanged()
         {
+            // Cancel previous loading task
+            _cancellationTokenSource.Cancel();
+            _cancellationTokenSource = new ();
+
             // TODO: track and cancel existing async preview tasks
             // https://github.com/microsoft/PowerToys/issues/22480
             if (File == null)
@@ -101,20 +111,30 @@ namespace Peek.FilePreviewer
             }
 
             Previewer = previewerFactory.Create(File);
-            await UpdatePreviewAsync();
+
+            await UpdatePreviewAsync(_cancellationTokenSource.Token);
         }
 
-        private async Task UpdatePreviewAsync()
+        private async Task UpdatePreviewAsync(CancellationToken cancellationToken)
         {
             if (Previewer != null)
             {
-                var size = await Previewer.GetPreviewSizeAsync();
-                SizeFormat windowSizeFormat = UnsupportedFilePreviewer != null ? SizeFormat.Percentage : SizeFormat.Pixels;
-                PreviewSizeChanged?.Invoke(this, new PreviewSizeChangedArgs(size, windowSizeFormat));
-                await Previewer.LoadPreviewAsync();
+                try
+                {
+                    cancellationToken.ThrowIfCancellationRequested();
+                    var size = await Previewer.GetPreviewSizeAsync(cancellationToken);
+                    SizeFormat windowSizeFormat = UnsupportedFilePreviewer != null ? SizeFormat.Percentage : SizeFormat.Pixels;
+                    PreviewSizeChanged?.Invoke(this, new PreviewSizeChangedArgs(size, windowSizeFormat));
+                    cancellationToken.ThrowIfCancellationRequested();
+                    await Previewer.LoadPreviewAsync(cancellationToken);
+                    cancellationToken.ThrowIfCancellationRequested();
+                    await UpdateImageTooltipAsync();
+                }
+                catch (OperationCanceledException)
+                {
+                    // TODO: Log task cancelled exception?
+                }
             }
-
-            await UpdateImageTooltipAsync();
         }
 
         partial void OnPreviewerChanging(IPreviewer? value)

src/modules/peek/Peek.FilePreviewer/Previewers/IPreviewer.cs

@@ -6,6 +6,7 @@ namespace Peek.FilePreviewer.Previewers
 {
     using System;
     using System.ComponentModel;
+    using System.Threading;
     using System.Threading.Tasks;
     using Windows.Foundation;
 
@@ -15,9 +16,9 @@ namespace Peek.FilePreviewer.Previewers
 
         public static bool IsFileTypeSupported(string fileExt) => throw new NotImplementedException();
 
-        public Task<Size> GetPreviewSizeAsync();
+        public Task<Size> GetPreviewSizeAsync(CancellationToken cancellationToken);
 
-        Task LoadPreviewAsync();
+        Task LoadPreviewAsync(CancellationToken cancellationToken);
     }
 
     public enum PreviewState

src/modules/peek/Peek.FilePreviewer/Previewers/ImagePreviewer/Helpers/PropertyHelper.cs

@@ -5,6 +5,7 @@
 namespace Peek.FilePreviewer.Previewers
 {
     using System;
+    using System.Diagnostics;
     using System.Runtime.InteropServices;
     using System.Threading.Tasks;
     using Peek.Common.Models;
@@ -16,14 +17,21 @@ namespace Peek.FilePreviewer.Previewers
         {
             return Task.Run(() =>
             {
-                var propertyStore = PropertyStoreShellApi.GetPropertyStoreFromPath(filePath, PropertyStoreShellApi.PropertyStoreFlags.OPENSLOWITEM);
-                if (propertyStore != null)
+                try
                 {
-                    var width = (int)PropertyStoreShellApi.GetUIntFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.ImageHorizontalSize);
-                    var height = (int)PropertyStoreShellApi.GetUIntFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.ImageVerticalSize);
+                    var propertyStore = PropertyStoreShellApi.GetPropertyStoreFromPath(filePath, PropertyStoreShellApi.PropertyStoreFlags.OPENSLOWITEM);
+                    if (propertyStore != null)
+                    {
+                        var width = (int)PropertyStoreShellApi.GetUIntFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.ImageHorizontalSize);
+                        var height = (int)PropertyStoreShellApi.GetUIntFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.ImageVerticalSize);
 
-                    Marshal.ReleaseComObject(propertyStore);
-                    return new Size(width, height);
+                        Marshal.ReleaseComObject(propertyStore);
+                        return new Size(width, height);
+                    }
+                }
+                catch (Exception e)
+                {
+                    Debug.Write("Error getting image dimensions:\n" + e.ToString());
                 }
 
                 return Size.Empty;
@@ -33,12 +41,19 @@ namespace Peek.FilePreviewer.Previewers
         public static Task<ulong> GetFileSizeInBytes(string filePath)
         {
             ulong bytes = 0;
-            var propertyStore = PropertyStoreShellApi.GetPropertyStoreFromPath(filePath, PropertyStoreShellApi.PropertyStoreFlags.OPENSLOWITEM);
-            if (propertyStore != null)
+            try
             {
-                bytes = PropertyStoreShellApi.GetULongFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.FileSizeBytes);
+                var propertyStore = PropertyStoreShellApi.GetPropertyStoreFromPath(filePath, PropertyStoreShellApi.PropertyStoreFlags.OPENSLOWITEM);
+                if (propertyStore != null)
+                {
+                    bytes = PropertyStoreShellApi.GetULongFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.FileSizeBytes);
 
-                Marshal.ReleaseComObject(propertyStore);
+                    Marshal.ReleaseComObject(propertyStore);
+                }
+            }
+            catch (Exception e)
+            {
+                Debug.WriteLine("Error getting folder item size:\n", e.ToString());
             }
 
             return Task.FromResult(bytes);
@@ -47,13 +62,20 @@ namespace Peek.FilePreviewer.Previewers
         public static Task<string> GetFileType(string filePath)
         {
             var type = string.Empty;
-            var propertyStore = PropertyStoreShellApi.GetPropertyStoreFromPath(filePath, PropertyStoreShellApi.PropertyStoreFlags.OPENSLOWITEM);
-            if (propertyStore != null)
+            try
             {
-                // TODO: find a way to get user friendly description
-                type = PropertyStoreShellApi.GetStringFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.FileType);
+                var propertyStore = PropertyStoreShellApi.GetPropertyStoreFromPath(filePath, PropertyStoreShellApi.PropertyStoreFlags.OPENSLOWITEM);
+                if (propertyStore != null)
+                {
+                    // TODO: find a way to get user friendly description
+                    type = PropertyStoreShellApi.GetStringFromPropertyStore(propertyStore, PropertyStoreShellApi.PropertyKey.FileType);
 
-                Marshal.ReleaseComObject(propertyStore);
+                    Marshal.ReleaseComObject(propertyStore);
+                }
+            }
+            catch (Exception e)
+            {
+                Debug.WriteLine("Failed to get file type:\n" + e.ToString());
             }
 
             return Task.FromResult(type);

src/modules/peek/Peek.FilePreviewer/Previewers/ImagePreviewer/ImagePreviewer.cs

@@ -49,18 +49,14 @@ namespace Peek.FilePreviewer.Previewers
 
         private bool IsFullImageLoaded => FullQualityImageTask?.Status == TaskStatus.RanToCompletion;
 
-        private CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
-
-        private CancellationToken CancellationToken => _cancellationTokenSource.Token;
-
         public void Dispose()
         {
-            _cancellationTokenSource.Dispose();
             GC.SuppressFinalize(this);
         }
 
-        public async Task<Size> GetPreviewSizeAsync()
+        public async Task<Size> GetPreviewSizeAsync(CancellationToken cancellationToken)
         {
+            cancellationToken.ThrowIfCancellationRequested();
             var propertyImageSize = await PropertyHelper.GetImageSize(File.Path);
             if (propertyImageSize != Size.Empty)
             {
@@ -70,13 +66,14 @@ namespace Peek.FilePreviewer.Previewers
             return await WICHelper.GetImageSize(File.Path);
         }
 
-        public async Task LoadPreviewAsync()
+        public async Task LoadPreviewAsync(CancellationToken cancellationToken)
         {
             State = PreviewState.Loading;
 
-            LowQualityThumbnailTask = LoadLowQualityThumbnailAsync();
-            HighQualityThumbnailTask = LoadHighQualityThumbnailAsync();
-            FullQualityImageTask = LoadFullQualityImageAsync();
+            LowQualityThumbnailTask = LoadLowQualityThumbnailAsync(cancellationToken);
+            HighQualityThumbnailTask = LoadHighQualityThumbnailAsync(cancellationToken);
+            FullQualityImageTask = LoadFullQualityImageAsync(cancellationToken);
+            cancellationToken.ThrowIfCancellationRequested();
 
             await Task.WhenAll(LowQualityThumbnailTask, HighQualityThumbnailTask, FullQualityImageTask);
 
@@ -97,15 +94,11 @@ namespace Peek.FilePreviewer.Previewers
             }
         }
 
-        private Task<bool> LoadLowQualityThumbnailAsync()
+        private Task<bool> LoadLowQualityThumbnailAsync(CancellationToken cancellationToken)
         {
             return TaskExtension.RunSafe(async () =>
             {
-                if (CancellationToken.IsCancellationRequested)
-                {
-                    _cancellationTokenSource = new CancellationTokenSource();
-                    return;
-                }
+                cancellationToken.ThrowIfCancellationRequested();
 
                 if (!IsFullImageLoaded && !IsHighQualityThumbnailLoaded)
                 {
@@ -117,24 +110,23 @@ namespace Peek.FilePreviewer.Previewers
                         throw new ArgumentNullException(nameof(hbitmap));
                     }
 
+                    cancellationToken.ThrowIfCancellationRequested();
+
                     await Dispatcher.RunOnUiThread(async () =>
                     {
-                        var thumbnailBitmap = await GetBitmapFromHBitmapAsync(hbitmap);
+                        cancellationToken.ThrowIfCancellationRequested();
+                        var thumbnailBitmap = await GetBitmapFromHBitmapAsync(hbitmap, cancellationToken);
                         Preview = thumbnailBitmap;
                     });
                 }
             });
         }
 
-        private Task<bool> LoadHighQualityThumbnailAsync()
+        private Task<bool> LoadHighQualityThumbnailAsync(CancellationToken cancellationToken)
         {
             return TaskExtension.RunSafe(async () =>
             {
-                if (CancellationToken.IsCancellationRequested)
-                {
-                    _cancellationTokenSource = new CancellationTokenSource();
-                    return;
-                }
+                cancellationToken.ThrowIfCancellationRequested();
 
                 if (!IsFullImageLoaded)
                 {
@@ -146,29 +138,29 @@ namespace Peek.FilePreviewer.Previewers
                         throw new ArgumentNullException(nameof(hbitmap));
                     }
 
+                    cancellationToken.ThrowIfCancellationRequested();
+
                     await Dispatcher.RunOnUiThread(async () =>
                     {
-                        var thumbnailBitmap = await GetBitmapFromHBitmapAsync(hbitmap);
+                        cancellationToken.ThrowIfCancellationRequested();
+                        var thumbnailBitmap = await GetBitmapFromHBitmapAsync(hbitmap, cancellationToken);
                         Preview = thumbnailBitmap;
                     });
                 }
             });
         }
 
-        private Task<bool> LoadFullQualityImageAsync()
+        private Task<bool> LoadFullQualityImageAsync(CancellationToken cancellationToken)
         {
             return TaskExtension.RunSafe(async () =>
             {
-                if (CancellationToken.IsCancellationRequested)
-                {
-                    _cancellationTokenSource = new CancellationTokenSource();
-                    return;
-                }
+                cancellationToken.ThrowIfCancellationRequested();
 
                 // TODO: Check if this is performant
                 await Dispatcher.RunOnUiThread(async () =>
                 {
-                    var bitmap = await GetFullBitmapFromPathAsync(File.Path);
+                    cancellationToken.ThrowIfCancellationRequested();
+                    var bitmap = await GetFullBitmapFromPathAsync(File.Path, cancellationToken);
                     Preview = bitmap;
                 });
             });
@@ -183,27 +175,34 @@ namespace Peek.FilePreviewer.Previewers
             return hasFailedLoadingLowQualityThumbnail && hasFailedLoadingHighQualityThumbnail && hasFailedLoadingFullQualityImage;
         }
 
-        private static async Task<BitmapImage> GetFullBitmapFromPathAsync(string path)
+        private static async Task<BitmapImage> GetFullBitmapFromPathAsync(string path, CancellationToken cancellationToken)
         {
             var bitmap = new BitmapImage();
+
+            cancellationToken.ThrowIfCancellationRequested();
             using (FileStream stream = System.IO.File.OpenRead(path))
             {
+                cancellationToken.ThrowIfCancellationRequested();
                 await bitmap.SetSourceAsync(stream.AsRandomAccessStream());
             }
 
             return bitmap;
         }
 
-        private static async Task<BitmapSource> GetBitmapFromHBitmapAsync(IntPtr hbitmap)
+        private static async Task<BitmapSource> GetBitmapFromHBitmapAsync(IntPtr hbitmap, CancellationToken cancellationToken)
         {
             try
             {
                 var bitmap = System.Drawing.Image.FromHbitmap(hbitmap);
                 var bitmapImage = new BitmapImage();
+
+                cancellationToken.ThrowIfCancellationRequested();
                 using (var stream = new MemoryStream())
                 {
                     bitmap.Save(stream, ImageFormat.Bmp);
                     stream.Position = 0;
+
+                    cancellationToken.ThrowIfCancellationRequested();
                     await bitmapImage.SetSourceAsync(stream.AsRandomAccessStream());
                 }
 

src/modules/peek/Peek.FilePreviewer/Previewers/PngPreviewer/PngPreviewer.cs

@@ -5,18 +5,16 @@
 namespace Peek.FilePreviewer.Previewers
 {
     using System;
-    using System.Collections.Generic;
-    using System.Drawing.Imaging;
     using System.IO;
     using System.Threading;
     using System.Threading.Tasks;
     using CommunityToolkit.Mvvm.ComponentModel;
     using Microsoft.UI.Dispatching;
     using Microsoft.UI.Xaml.Media.Imaging;
-    using Peek.Common;
+    using Peek.Common.Extensions;
     using Windows.Foundation;
     using Windows.Graphics.Imaging;
-    using Windows.Storage.Streams;
+    using Windows.Storage;
     using File = Peek.Common.Models.File;
 
     public partial class PngPreviewer : ObservableObject, IBitmapPreviewer
@@ -44,17 +42,23 @@ namespace Peek.FilePreviewer.Previewers
 
         private DispatcherQueue Dispatcher { get; }
 
+        private Task<bool>? PreviewQualityThumbnailTask { get; set; }
+
+        private Task<bool>? FullQualityImageTask { get; set; }
+
         private CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
 
         private CancellationToken CancellationToken => _cancellationTokenSource.Token;
 
+        private bool IsFullImageLoaded => FullQualityImageTask?.Status == TaskStatus.RanToCompletion;
+
         public void Dispose()
         {
             _cancellationTokenSource.Dispose();
             GC.SuppressFinalize(this);
         }
 
-        public async Task<Size> GetPreviewSizeAsync()
+        public async Task<Size> GetPreviewSizeAsync(CancellationToken cancellationToken)
         {
             var propertyImageSize = await PropertyHelper.GetImageSize(File.Path);
             if (propertyImageSize != Size.Empty)
@@ -65,13 +69,14 @@ namespace Peek.FilePreviewer.Previewers
             return await WICHelper.GetImageSize(File.Path);
         }
 
-        public async Task LoadPreviewAsync()
+        public async Task LoadPreviewAsync(CancellationToken cancellationToken)
         {
             State = PreviewState.Loading;
 
-            var previewTask = LoadPreviewImageAsync();
+            PreviewQualityThumbnailTask = LoadPreviewImageAsync();
+            FullQualityImageTask = LoadFullImageAsync();
 
-            await Task.WhenAll(previewTask);
+            await Task.WhenAll(PreviewQualityThumbnailTask, FullQualityImageTask);
 
             if (Preview == null)
             {
@@ -95,10 +100,10 @@ namespace Peek.FilePreviewer.Previewers
             }
         }
 
-        private Task LoadPreviewImageAsync()
+        private Task<bool> LoadPreviewImageAsync()
         {
             var thumbnailTCS = new TaskCompletionSource();
-            Dispatcher.TryEnqueue(async () =>
+            return TaskExtension.RunSafe(async () =>
             {
                 if (CancellationToken.IsCancellationRequested)
                 {
@@ -106,12 +111,51 @@ namespace Peek.FilePreviewer.Previewers
                     return;
                 }
 
-                Preview = await ThumbnailHelper.GetThumbnailAsync(File.Path, _png_image_size);
-
-                thumbnailTCS.SetResult();
+                if (!IsFullImageLoaded)
+                {
+                    await Dispatcher.RunOnUiThread(async () =>
+                    {
+                        Preview = await ThumbnailHelper.GetThumbnailAsync(File.Path, _png_image_size);
+                    });
+                }
             });
+        }
 
-            return thumbnailTCS.Task;
+        private Task<bool> LoadFullImageAsync()
+        {
+            var thumbnailTCS = new TaskCompletionSource();
+            return TaskExtension.RunSafe(async () =>
+            {
+                if (CancellationToken.IsCancellationRequested)
+                {
+                    _cancellationTokenSource = new CancellationTokenSource();
+                    return;
+                }
+
+                await Dispatcher.RunOnUiThread(async () =>
+                {
+                    WriteableBitmap? bitmap = null;
+
+                    var sFile = await StorageFile.GetFileFromPathAsync(File.Path);
+                    using (var randomAccessStream = await sFile.OpenStreamForReadAsync())
+                    {
+                        // Create an encoder with the desired format
+                        var decoder = await BitmapDecoder.CreateAsync(
+                            BitmapDecoder.PngDecoderId,
+                            randomAccessStream.AsRandomAccessStream());
+
+                        var softwareBitmap = await decoder.GetSoftwareBitmapAsync(
+                            BitmapPixelFormat.Bgra8,
+                            BitmapAlphaMode.Premultiplied);
+
+                        // full quality image
+                        bitmap = new WriteableBitmap((int)decoder.PixelWidth, (int)decoder.PixelHeight);
+                        softwareBitmap?.CopyToBuffer(bitmap.PixelBuffer);
+                    }
+
+                    Preview = bitmap;
+                });
+            });
         }
     }
 }

src/modules/peek/Peek.FilePreviewer/Previewers/PreviewerFactory.cs

@@ -4,6 +4,7 @@
 
 namespace Peek.FilePreviewer.Previewers
 {
+    using System.Threading;
     using Peek.Common.Models;
 
     public class PreviewerFactory

src/modules/peek/Peek.FilePreviewer/Previewers/UnsupportedFilePreviewer/UnsupportedFilePreviewer.cs

@@ -70,21 +70,16 @@ namespace Peek.FilePreviewer.Previewers
 
         private DispatcherQueue Dispatcher { get; }
 
-        private CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
-
-        private CancellationToken CancellationToken => _cancellationTokenSource.Token;
-
         private Task<bool>? IconPreviewTask { get; set; }
 
         private Task<bool>? DisplayInfoTask { get; set; }
 
         public void Dispose()
         {
-            _cancellationTokenSource.Dispose();
             GC.SuppressFinalize(this);
         }
 
-        public Task<Size> GetPreviewSizeAsync()
+        public Task<Size> GetPreviewSizeAsync(CancellationToken cancellationToken)
         {
             return Task.Run(() =>
             {
@@ -92,12 +87,14 @@ namespace Peek.FilePreviewer.Previewers
             });
         }
 
-        public async Task LoadPreviewAsync()
+        public async Task LoadPreviewAsync(CancellationToken cancellationToken)
         {
+            cancellationToken.ThrowIfCancellationRequested();
+
             State = PreviewState.Loading;
 
-            IconPreviewTask = LoadIconPreviewAsync();
-            DisplayInfoTask = LoadDisplayInfoAsync();
+            IconPreviewTask = LoadIconPreviewAsync(cancellationToken);
+            DisplayInfoTask = LoadDisplayInfoAsync(cancellationToken);
 
             await Task.WhenAll(IconPreviewTask, DisplayInfoTask);
 
@@ -107,38 +104,34 @@ namespace Peek.FilePreviewer.Previewers
             }
         }
 
-        public Task<bool> LoadIconPreviewAsync()
+        public Task<bool> LoadIconPreviewAsync(CancellationToken cancellationToken)
         {
             return TaskExtension.RunSafe(async () =>
             {
-                if (CancellationToken.IsCancellationRequested)
-                {
-                    _cancellationTokenSource = new CancellationTokenSource();
-                    return;
-                }
+                cancellationToken.ThrowIfCancellationRequested();
 
                 // TODO: Get icon with transparency
                 IconHelper.GetIcon(Path.GetFullPath(File.Path), out IntPtr hbitmap);
+
+                cancellationToken.ThrowIfCancellationRequested();
                 await Dispatcher.RunOnUiThread(async () =>
                 {
-                    var iconBitmap = await GetBitmapFromHBitmapAsync(hbitmap);
+                    cancellationToken.ThrowIfCancellationRequested();
+                    var iconBitmap = await GetBitmapFromHBitmapAsync(hbitmap, cancellationToken);
                     IconPreview = iconBitmap;
                 });
             });
         }
 
-        public Task<bool> LoadDisplayInfoAsync()
+        public Task<bool> LoadDisplayInfoAsync(CancellationToken cancellationToken)
         {
             return TaskExtension.RunSafe(async () =>
             {
-                if (CancellationToken.IsCancellationRequested)
-                {
-                    _cancellationTokenSource = new CancellationTokenSource();
-                    return;
-                }
-
                 // File Properties
+                cancellationToken.ThrowIfCancellationRequested();
                 var bytes = await PropertyHelper.GetFileSizeInBytes(File.Path);
+
+                cancellationToken.ThrowIfCancellationRequested();
                 var type = await PropertyHelper.GetFileType(File.Path);
 
                 await Dispatcher.RunOnUiThread(() =>
@@ -169,17 +162,22 @@ namespace Peek.FilePreviewer.Previewers
             return hasFailedLoadingIconPreview && hasFailedLoadingDisplayInfo;
         }
 
-        // TODO: Move this to a helper file (ImagePrevier uses the same code)
-        private static async Task<BitmapSource> GetBitmapFromHBitmapAsync(IntPtr hbitmap)
+        // TODO: Move this to a helper file (ImagePreviewer uses the same code)
+        private static async Task<BitmapSource> GetBitmapFromHBitmapAsync(IntPtr hbitmap, CancellationToken cancellationToken)
         {
             try
             {
+                cancellationToken.ThrowIfCancellationRequested();
                 var bitmap = System.Drawing.Image.FromHbitmap(hbitmap);
                 var bitmapImage = new BitmapImage();
+
+                cancellationToken.ThrowIfCancellationRequested();
                 using (var stream = new MemoryStream())
                 {
                     bitmap.Save(stream, ImageFormat.Bmp);
                     stream.Position = 0;
+
+                    cancellationToken.ThrowIfCancellationRequested();
                     await bitmapImage.SetSourceAsync(stream.AsRandomAccessStream());
                 }
 

src/modules/peek/Peek.FilePreviewer/Previewers/WebBrowserPreviewer/WebBrowserPreviewer.cs

@@ -9,8 +9,6 @@ namespace Peek.FilePreviewer.Previewers
     using System.Threading;
     using System.Threading.Tasks;
     using CommunityToolkit.Mvvm.ComponentModel;
-    using Microsoft.UI.Dispatching;
-    using Peek.FilePreviewer.Controls;
     using Windows.Foundation;
     using File = Peek.Common.Models.File;
 
@@ -39,14 +37,14 @@ namespace Peek.FilePreviewer.Previewers
 
         private File File { get; }
 
-        public Task<Size> GetPreviewSizeAsync()
+        public Task<Size> GetPreviewSizeAsync(CancellationToken cancellationToken)
         {
             // TODO: define how to proper window size on HTML content.
             var size = new Size(1280, 720);
             return Task.FromResult(size);
         }
 
-        public Task LoadPreviewAsync()
+        public Task LoadPreviewAsync(CancellationToken cancellationToken)
         {
             State = PreviewState.Loading;
 

src/modules/peek/Peek.UI/FolderItemSources/IFolderItemsSource.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Peek.UI.FolderItemSources
+{
+    using System.Threading.Tasks;
+    using Peek.Common.Models;
+    using Shell32;
+
+    public interface IFolderItemsSource
+    {
+        // Result is null if no file at index
+        public Task<File?> GetItemAt(uint index);
+
+        public Task<InitialQueryData?> Initialize(IShellFolderViewDual3 folderView);
+    }
+
+    public struct InitialQueryData
+    {
+        public uint FirstItemIndex { get; set; }
+
+        public uint ItemsCount { get; set; }
+    }
+}

src/modules/peek/Peek.UI/FolderItemSources/SelectedItemsSource.cs

@@ -0,0 +1,24 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Peek.UI.FolderItemSources
+{
+    using System.Threading.Tasks;
+    using Peek.Common.Models;
+    using Shell32;
+
+    // Source of folder items for use when user activates Peek with multiple selected files
+    public class SelectedItemsSource : IFolderItemsSource
+    {
+        public Task<File?> GetItemAt(uint index)
+        {
+            throw new System.NotImplementedException();
+        }
+
+        public Task<InitialQueryData?> Initialize(IShellFolderViewDual3 folderView)
+        {
+            throw new System.NotImplementedException();
+        }
+    }
+}

src/modules/peek/Peek.UI/FolderItemSources/WholeFolderItemsSource.cs

@@ -0,0 +1,112 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Peek.UI.FolderItemSources
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Diagnostics;
+    using System.Linq;
+    using System.Threading.Tasks;
+    using Peek.Common.Models;
+    using Shell32;
+    using Windows.Storage;
+    using Windows.Storage.Search;
+
+    // Provides folder items across an entire folder
+    public class WholeFolderItemsSource : IFolderItemsSource
+    {
+        private StorageItemQueryResult? ItemQuery { get; set; } = null;
+
+        public async Task<File?> GetItemAt(uint index)
+        {
+            if (ItemQuery == null)
+            {
+                return null;
+            }
+
+            IReadOnlyList<IStorageItem> items;
+            try
+            {
+                // ~1ms runtime on workstation w/ a debugger attached.
+                // TODO: further optimize by pre-fetching and maintaining a window of items.
+                //  There's a win32 API FindNextFile we could have used, but it doesn't allow fast, reverse iteration,
+                //  which is needed for backwards navigation.
+                items = await ItemQuery.GetItemsAsync(index, 1);
+                if (items == null || items.Count == 0)
+                {
+                    return null;
+                }
+            }
+            catch (Exception e)
+            {
+                Debug.WriteLine("Caught exception attempting to get file:\n", e.ToString());
+                return null;
+            }
+
+            // TODO: optimize by adding StorageItem as field to File class
+            return new File(items.First().Path);
+        }
+
+        public async Task<InitialQueryData?> Initialize(IShellFolderViewDual3 folderView)
+        {
+            try
+            {
+                var selectedItems = folderView.SelectedItems();
+                if (selectedItems == null || selectedItems.Count == 0)
+                {
+                    return null;
+                }
+
+                Debug.Assert(selectedItems.Count == 1, "SelectedItemsSource is intended for multi-item activations");
+
+                var selectedItem = selectedItems.Item(0);
+                var parent = System.IO.Directory.GetParent(selectedItem.Path); // TODO: try get directory name instead
+                if (parent == null)
+                {
+                    return null;
+                }
+
+                var folder = await StorageFolder.GetFolderFromPathAsync(parent.FullName);
+
+                // TODO: check if query options are supported (member helpers)
+                var queryOptions = new QueryOptions();
+                queryOptions.IndexerOption = IndexerOption.UseIndexerWhenAvailable;
+
+                // TODO: check if this clear is actually needed
+                Debug.WriteLine("count: " + queryOptions.SortOrder.Count);
+                queryOptions.SortOrder.Clear();
+
+                // TODO: fetch sort option
+                queryOptions.SortOrder.Add(new SortEntry("System.Size", false));
+
+                ItemQuery = folder.CreateItemQuery();
+                ItemQuery.ApplyNewQueryOptions(queryOptions);
+
+                Debug.WriteLine(selectedItem.Name);
+
+                // TODO: property passed in depends on sort order passed to query
+                var firstItemIndex = await ItemQuery.FindStartIndexAsync(selectedItem.Size);
+
+                // FindStartIndexAsync returns this when no item found
+                if (firstItemIndex == uint.MaxValue)
+                {
+                    Debug.WriteLine("File not found");
+                    return null;
+                }
+
+                InitialQueryData result = new ();
+
+                // TODO: pass & throw cancellation token (not essential, but may free thread resources earlier)
+                result.ItemsCount = await ItemQuery.GetItemCountAsync();
+                result.FirstItemIndex = firstItemIndex;
+                return result;
+            }
+            catch (Exception)
+            {
+                return null;
+            }
+        }
+    }
+}

src/modules/peek/Peek.UI/FolderItemsQuery.cs

@@ -7,12 +7,16 @@ namespace Peek.UI
     using System;
     using System.Collections.Generic;
     using System.Diagnostics;
+    using System.Linq;
     using System.Threading;
     using System.Threading.Tasks;
     using CommunityToolkit.Mvvm.ComponentModel;
     using Microsoft.UI.Dispatching;
     using Peek.Common.Models;
+    using Peek.UI.FolderItemSources;
     using Peek.UI.Helpers;
+    using Windows.Storage;
+    using Windows.Storage.Search;
 
     public partial class FolderItemsQuery : ObservableObject
     {
@@ -24,7 +28,7 @@ namespace Peek.UI
         private File? currentFile;
 
         [ObservableProperty]
-        private List<File> files = new ();
+        private int itemsCount = 0;
 
         [ObservableProperty]
         private bool isMultiSelection;
@@ -34,52 +38,66 @@ namespace Peek.UI
 
         private CancellationTokenSource CancellationTokenSource { get; set; } = new CancellationTokenSource();
 
-        private Task? InitializeFilesTask { get; set; } = null;
+        private Task? InitializeQueryTask { get; set; } = null;
 
+        private IFolderItemsSource? FolderItemsSource { get; set; } = null;
+
+        // Must be called from UI thread
         public void Clear()
         {
             CurrentFile = null;
             IsMultiSelection = false;
 
-            if (InitializeFilesTask != null && InitializeFilesTask.Status == TaskStatus.Running)
+            if (InitializeQueryTask != null && InitializeQueryTask.Status == TaskStatus.Running)
             {
-                Debug.WriteLine("Detected existing initializeFilesTask running. Cancelling it..");
+                Debug.WriteLine("Detected existing InitializeQueryTask running. Cancelling it..");
                 CancellationTokenSource.Cancel();
             }
 
-            InitializeFilesTask = null;
+            InitializeQueryTask = null;
 
             lock (_mutateQueryDataLock)
             {
-                _dispatcherQueue.TryEnqueue(() =>
-                {
-                    Files = new List<File>();
-                    CurrentItemIndex = UninitializedItemIndex;
-                });
+                ItemsCount = 0; // TODO: can maybe move outside?
+                CurrentItemIndex = UninitializedItemIndex;
             }
         }
 
-        public void UpdateCurrentItemIndex(int desiredIndex)
+        // Must be called from UI thread
+        public async Task UpdateCurrentItemIndex(int desiredIndex)
         {
-            if (Files.Count <= 1 || CurrentItemIndex == UninitializedItemIndex ||
-                (InitializeFilesTask != null && InitializeFilesTask.Status == TaskStatus.Running))
+            // TODO: add items count check
+            if (ItemsCount <= 1 || CurrentItemIndex == UninitializedItemIndex || FolderItemsSource == null ||
+                (InitializeQueryTask != null && InitializeQueryTask.Status == TaskStatus.Running))
             {
                 return;
             }
 
             // Current index wraps around when reaching min/max folder item indices
-            desiredIndex %= Files.Count;
-            CurrentItemIndex = desiredIndex < 0 ? Files.Count + desiredIndex : desiredIndex;
+            desiredIndex %= itemsCount;
+            CurrentItemIndex = desiredIndex < 0 ? itemsCount + desiredIndex : desiredIndex;
 
-            if (CurrentItemIndex < 0 || CurrentItemIndex >= Files.Count)
+            if (CurrentItemIndex < 0 || CurrentItemIndex >= itemsCount)
             {
                 Debug.Assert(false, "Out of bounds folder item index detected.");
                 CurrentItemIndex = 0;
             }
 
-            CurrentFile = Files[CurrentItemIndex];
+            if (FolderItemsSource == null)
+            {
+                return;
+            }
+
+            var temp = await FolderItemsSource.GetItemAt((uint)CurrentItemIndex); // TODO: fix uint declarations
+            if (temp != null)
+            {
+                Debug.WriteLine("Navigated to " + temp.FileName);
+            }
+
+            CurrentFile = temp;
         }
 
+        // Must be called from UI thread
         public void Start()
         {
             var folderView = FileExplorerHelper.GetCurrentFolderView();
@@ -108,75 +126,54 @@ namespace Peek.UI
 
             try
             {
-                if (InitializeFilesTask != null && InitializeFilesTask.Status == TaskStatus.Running)
+                if (InitializeQueryTask != null && InitializeQueryTask.Status == TaskStatus.Running)
                 {
-                    Debug.WriteLine("Detected unexpected existing initializeFilesTask running. Cancelling it..");
+                    Debug.WriteLine("Detected unexpected existing InitializeQueryTask running. Cancelling it..");
                     CancellationTokenSource.Cancel();
                 }
 
                 CancellationTokenSource = new CancellationTokenSource();
-                InitializeFilesTask = new Task(() => InitializeFiles(items, firstSelectedItem, CancellationTokenSource.Token));
+                InitializeQueryTask = new Task(() => InitializeQuery(folderView, items, firstSelectedItem, CancellationTokenSource.Token));
 
                 // Execute file initialization/querying on background thread
-                InitializeFilesTask.Start();
+                InitializeQueryTask.Start();
             }
             catch (Exception e)
             {
-                Debug.WriteLine("Exception trying to run initializeFilesTask:\n" + e.ToString());
+                Debug.WriteLine("Exception trying to run InitializeQueryTask:\n" + e.ToString());
             }
         }
 
-        // Finds index of firstSelectedItem either amongst folder items, initializing our internal File list
-        //  since storing Shell32.FolderItems as a field isn't reliable.
-        // Can take a few seconds for folders with 1000s of items; ensure it runs on a background thread.
-        //
-        // TODO optimization:
-        //  Handle case where selected items count > 1 separately. Although it'll still be slow for 1000s of items selected,
-        //  we can leverage faster APIs like Windows.Storage when 1 item is selected, and navigation is scoped to
-        //  the entire folder. We can then avoid iterating through all items here, and maintain a dynamic window of
-        //  loaded items around the current item index.
-        private void InitializeFiles(
+        private async void InitializeQuery(
+            Shell32.IShellFolderViewDual3 folderView, // TODO: remove
             Shell32.FolderItems items,
             Shell32.FolderItem firstSelectedItem,
             CancellationToken cancellationToken)
         {
-            var tempFiles = new List<File>(items.Count);
-            var tempCurIndex = UninitializedItemIndex;
+            FolderItemsSource = IsMultiSelection ? new SelectedItemsSource() : new WholeFolderItemsSource();
 
-            for (int i = 0; i < items.Count; i++)
+            InitialQueryData? initialQueryData = await FolderItemsSource.Initialize(folderView);
+            if (initialQueryData == null || !initialQueryData.HasValue)
             {
-                cancellationToken.ThrowIfCancellationRequested();
-
-                var item = items.Item(i);
-                if (item == null)
-                {
-                    continue;
-                }
-
-                if (item.Name == firstSelectedItem.Name)
-                {
-                    tempCurIndex = i;
-                }
-
-                tempFiles.Add(new File(item.Path));
-            }
-
-            if (tempCurIndex == UninitializedItemIndex)
-            {
-                Debug.WriteLine("File query initialization: selectedItem index not found. Navigation remains disabled.");
                 return;
             }
 
+            InitialQueryData y = new ();
+            y.FirstItemIndex = 0;
+
             cancellationToken.ThrowIfCancellationRequested();
 
+            // Lock to prevent race conditions with UI thread's Clear calls upon Peek deactivation/hide
             lock (_mutateQueryDataLock)
             {
                 cancellationToken.ThrowIfCancellationRequested();
 
                 _dispatcherQueue.TryEnqueue(() =>
                 {
-                    Files = tempFiles;
-                    CurrentItemIndex = tempCurIndex;
+                    cancellationToken.ThrowIfCancellationRequested();
+
+                    ItemsCount = (int)initialQueryData.Value.ItemsCount; // TODO: remove cast
+                    CurrentItemIndex = (int)initialQueryData.Value.FirstItemIndex;
                 });
             }
         }

src/modules/peek/Peek.UI/Helpers/FileExplorerHelper.cs

@@ -13,7 +13,7 @@ namespace Peek.UI.Helpers
 {
     public static class FileExplorerHelper
     {
-        public static Shell32.IShellFolderViewDual2? GetCurrentFolderView()
+        public static Shell32.IShellFolderViewDual3? GetCurrentFolderView()
         {
             var foregroundWindowHandle = NativeMethods.GetForegroundWindow();
 
@@ -26,7 +26,7 @@ namespace Peek.UI.Helpers
             var shell = new Shell32.Shell();
             foreach (SHDocVw.InternetExplorer window in shell.Windows())
             {
-                var shellFolderView = (Shell32.IShellFolderViewDual2)window.Document;
+                var shellFolderView = (Shell32.IShellFolderViewDual3)window.Document;
                 var folderTitle = shellFolderView.Folder.Title;
 
                 if (window.HWND == (int)foregroundWindowHandle && folderTitle == foregroundWindowTitle)

src/modules/peek/Peek.UI/MainWindow.xaml

@@ -32,7 +32,7 @@
             File="{x:Bind ViewModel.FolderItemsQuery.CurrentFile, Mode=OneWay}"
             FileIndex="{x:Bind ViewModel.FolderItemsQuery.CurrentItemIndex, Mode=OneWay}"
             IsMultiSelection="{x:Bind ViewModel.FolderItemsQuery.IsMultiSelection, Mode=OneWay}"
-            NumberOfFiles="{x:Bind ViewModel.FolderItemsQuery.Files.Count, Mode=OneWay}" />
+            NumberOfFiles="{x:Bind ViewModel.FolderItemsQuery.ItemsCount, Mode=OneWay}" />
 
         <fp:FilePreview
             Grid.Row="1"

src/modules/peek/Peek.UI/MainWindowViewModel.cs

@@ -12,36 +12,39 @@ namespace Peek.UI
     {
         private const int NavigationThrottleDelayMs = 100;
 
+        private bool IsNavigating { get; set; } = false;
+
         public MainWindowViewModel()
         {
             NavigationThrottleTimer.Tick += NavigationThrottleTimer_Tick;
             NavigationThrottleTimer.Interval = TimeSpan.FromMilliseconds(NavigationThrottleDelayMs);
         }
 
-        public void AttemptLeftNavigation()
+        private async void AttemptNavigation(bool goToNextItem)
         {
-            if (NavigationThrottleTimer.IsEnabled)
+            if (NavigationThrottleTimer.IsEnabled && !IsNavigating)
             {
                 return;
             }
 
+            IsNavigating = true;
             NavigationThrottleTimer.Start();
 
-            // TODO: return a bool so UI can give feedback in case navigation is unavailable
-            FolderItemsQuery.UpdateCurrentItemIndex(FolderItemsQuery.CurrentItemIndex - 1);
+            var desiredItemIndex = FolderItemsQuery.CurrentItemIndex + (goToNextItem ? 1 : -1);
+
+            // TODO: return a bool so UI can give feedback in case navigation is unavailable?
+            await FolderItemsQuery.UpdateCurrentItemIndex(desiredItemIndex);
+            IsNavigating = false;
+        }
+
+        public void AttemptLeftNavigation()
+        {
+            AttemptNavigation(false);
         }
 
         public void AttemptRightNavigation()
         {
-            if (NavigationThrottleTimer.IsEnabled)
-            {
-                return;
-            }
-
-            NavigationThrottleTimer.Start();
-
-            // TODO: return a bool so UI can give feedback in case navigation is unavailable
-            FolderItemsQuery.UpdateCurrentItemIndex(FolderItemsQuery.CurrentItemIndex + 1);
+            AttemptNavigation(true);
         }
 
         private void NavigationThrottleTimer_Tick(object? sender, object e)