Feature: Support setting multiple images as desktop background (#9712)

Author: QuaintMako

src/Files.Uwp/BaseLayout.cs

@@ -648,7 +648,7 @@ private async Task LoadMenuItemsAsync()
             }
             shellContextMenuItemCancellationToken?.Cancel();
             shellContextMenuItemCancellationToken = new CancellationTokenSource();
-            SelectedItemsPropertiesViewModel.CheckFileExtension(SelectedItem?.FileExtension);
+            SelectedItemsPropertiesViewModel.CheckAllFileExtensions(this.SelectedItems.Select(selectedItem => selectedItem?.FileExtension).ToList());
             var shiftPressed = Window.Current.CoreWindow.GetKeyState(VirtualKey.Shift).HasFlag(CoreVirtualKeyStates.Down);
             var items = ContextFlyoutItemHelper.GetItemContextCommandsWithoutShellItems(currentInstanceViewModel: InstanceViewModel, workingDir: ParentShellPageInstance.FilesystemViewModel.WorkingDirectory, selectedItems: SelectedItems, selectedItemsPropertiesViewModel: SelectedItemsPropertiesViewModel, commandsViewModel: CommandsViewModel, shiftPressed: shiftPressed, showOpenMenu: false);
             ItemContextMenuFlyout.PrimaryCommands.Clear();

src/Files.Uwp/Helpers/ContextFlyoutItemHelper.cs

@@ -727,6 +727,7 @@ public static List<ContextMenuFlyoutItemViewModel> GetBaseItemMenuItems(BaseLayo
                             Glyph = "\uE91B",
                             Command = commandsViewModel.SetAsDesktopBackgroundItemCommand,
                             ShowInSearchPage = true,
+                            ShowItem = (selectedItemsPropertiesViewModel.SelectedItemsCount == 1)
                         },
                         new ContextMenuFlyoutItemViewModel()
                         {
@@ -735,6 +736,16 @@ public static List<ContextMenuFlyoutItemViewModel> GetBaseItemMenuItems(BaseLayo
                             GlyphFontFamilyName = "CustomGlyph",
                             Command = commandsViewModel.SetAsLockscreenBackgroundItemCommand,
                             ShowInSearchPage = true,
+                            ShowItem = (selectedItemsPropertiesViewModel.SelectedItemsCount == 1)
+                        },
+                        new ContextMenuFlyoutItemViewModel()
+                        {
+                            Text = "SetAsSlideshow".GetLocalized(),
+                            Glyph = "\uE91B",
+                            GlyphFontFamilyName = "CustomGlyph",
+                            Command = commandsViewModel.SetAsDesktopBackgroundItemCommand,
+                            ShowInSearchPage = true,
+                            ShowItem = (selectedItemsPropertiesViewModel.SelectedItemsCount > 1)
                         },
                     }
                 },

src/Files.Uwp/Helpers/FileExtensionHelpers.cs

@@ -88,5 +88,22 @@ public static bool IsFontFile(string fileExtensionToCheck)
                      fileExtensionToCheck.Equals(".ttc", StringComparison.OrdinalIgnoreCase) ||
                      fileExtensionToCheck.Equals(".ttf", StringComparison.OrdinalIgnoreCase);
         }
+
+        /// <summary>
+        /// Check if the file extension is a shortcut file.
+        /// </summary>
+        /// <param name="fileExtensionToCheck">The file extension to check.</param>
+        /// <returns><c>true</c> if the fileExtensionToCheck is a shortcute file;
+        /// otherwise <c>false</c>.</returns>
+        /// <remarks>Font file type is .lnkf</remarks>
+        public static bool IsShortcutFile(string fileExtensionToCheck)
+        {
+            if (string.IsNullOrEmpty(fileExtensionToCheck))
+            {
+                return false;
+            }
+
+            return fileExtensionToCheck.Equals(".lnk", StringComparison.OrdinalIgnoreCase);
+        }
     }
 }

src/Files.Uwp/ViewModels/SelectedItemsPropertiesViewModel.cs

@@ -5,6 +5,8 @@
 using System;
 using System.Collections.ObjectModel;
 using Windows.UI.Xaml;
+using System.Collections.Generic;
+using Files.Uwp.Helpers;
 
 namespace Files.Uwp.ViewModels
 {
@@ -537,29 +539,12 @@ public bool IsSelectedItemShortcut
             set => SetProperty(ref isSelectedItemShortcut, value);
         }
 
-        public void CheckFileExtension(string itemExtension)
+        public void CheckAllFileExtensions(List<string> itemExtensions)
         {
-            // Set properties to false
-            IsSelectedItemImage = false;
-            IsSelectedItemShortcut = false;
-
-            //check if the selected item is an image file
-            if (!string.IsNullOrEmpty(itemExtension) && SelectedItemsCount == 1)
-            {
-                if (itemExtension.Equals(".png", StringComparison.OrdinalIgnoreCase)
-                || itemExtension.Equals(".jpg", StringComparison.OrdinalIgnoreCase)
-                || itemExtension.Equals(".bmp", StringComparison.OrdinalIgnoreCase)
-                || itemExtension.Equals(".jpeg", StringComparison.OrdinalIgnoreCase))
-                {
-                    // Since item is an image, set the IsSelectedItemImage property to true
-                    IsSelectedItemImage = true;
-                }
-                else if (itemExtension.Equals(".lnk", StringComparison.OrdinalIgnoreCase))
-                {
-                    // The selected item is a shortcut, so set the IsSelectedItemShortcut property to true
-                    IsSelectedItemShortcut = true;
-                }
-            }
+            // Checks if all the item extensions are image extensions of some kind.
+            IsSelectedItemImage = itemExtensions.TrueForAll(itemExtension => FileExtensionHelpers.IsImageFile(itemExtension));
+            // Checks if there is only one selected item and if it's a shortcut.
+            IsSelectedItemShortcut = (itemExtensions.Count == 1) && (itemExtensions.TrueForAll(itemExtension => FileExtensionHelpers.IsShortcutFile(itemExtension)));
         }
 
         private string shortcutItemType;