CmdPal: Prevent item template selectors from modifying containers (#45498)

## Summary of the Pull Request

This PR updates the item template selectors for ListView and GridView
and prevents them from modifying the container.
As a flyby, it introduces an enum for the list item type and centralizes
the logic that determines the type to the view model.

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## PR Checklist

- [x] Closes: #45496 
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issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
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- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Core/Microsoft.CmdPal.Core.ViewModels/CommandViewModel.cs

@@ -11,6 +11,8 @@ public partial class CommandViewModel : ExtensionObjectViewModel
 {
     public ExtensionObject<ICommand> Model { get; private set; } = new(null);
 
+    public bool IsSet => Model.Unsafe is not null;
+
     protected bool IsInitialized { get; private set; }
 
     protected bool IsFastInitialized { get; private set; }

src/modules/cmdpal/Core/Microsoft.CmdPal.Core.ViewModels/ListItemType.cs

@@ -0,0 +1,12 @@
+// 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 Microsoft.CmdPal.Core.ViewModels;
+
+public enum ListItemType
+{
+    Item,
+    SectionHeader,
+    Separator,
+}

src/modules/cmdpal/Core/Microsoft.CmdPal.Core.ViewModels/ListItemViewModel.cs

@@ -24,7 +24,9 @@ public partial class ListItemViewModel : CommandItemViewModel
 
     public string Section { get; private set; } = string.Empty;
 
-    public bool IsSectionOrSeparator { get; private set; }
+    public ListItemType Type { get; private set; }
+
+    public bool IsInteractive => Type == ListItemType.Item;
 
     public DetailsViewModel? Details { get; private set; }
 
@@ -85,15 +87,17 @@ public partial class ListItemViewModel : CommandItemViewModel
 
         UpdateTags(li.Tags);
         Section = li.Section ?? string.Empty;
-        IsSectionOrSeparator = IsSeparator(li);
-        UpdateProperty(nameof(Section), nameof(IsSectionOrSeparator));
+        Type = EvaluateType();
+        UpdateProperty(nameof(Section), nameof(Type), nameof(IsInteractive));
 
         UpdateAccessibleName();
     }
 
-    private bool IsSeparator(IListItem item)
+    private ListItemType EvaluateType()
     {
-        return item.Command is null;
+        return Command.IsSet
+            ? ListItemType.Item
+            : string.IsNullOrEmpty(Section) ? ListItemType.Separator : ListItemType.SectionHeader;
     }
 
     public override void SlowInitializeProperties()
@@ -140,12 +144,12 @@ public partial class ListItemViewModel : CommandItemViewModel
                 break;
             case nameof(model.Section):
                 Section = model.Section ?? string.Empty;
-                IsSectionOrSeparator = IsSeparator(model);
-                UpdateProperty(nameof(Section), nameof(IsSectionOrSeparator));
+                Type = EvaluateType();
+                UpdateProperty(nameof(Section), nameof(Type), nameof(IsInteractive));
                 break;
             case nameof(model.Command):
-                IsSectionOrSeparator = IsSeparator(model);
-                UpdateProperty(nameof(IsSectionOrSeparator));
+                Type = EvaluateType();
+                UpdateProperty(nameof(Type), nameof(IsInteractive));
                 break;
             case nameof(Details):
                 var extensionDetails = model.Details;

src/modules/cmdpal/Microsoft.CmdPal.UI/Converters/GridItemContainerStyleSelector.cs

@@ -24,11 +24,19 @@ internal sealed partial class GridItemContainerStyleSelector : StyleSelector
 
     protected override Style? SelectStyleCore(object item, DependencyObject container)
     {
-        if (item is ListItemViewModel { IsSectionOrSeparator: true } listItem)
+        if (item is not ListItemViewModel element)
         {
-            return string.IsNullOrWhiteSpace(listItem.Title)
-                ? Separator!
-                : Section;
+            return Medium;
+        }
+
+        switch (element.Type)
+        {
+            case ListItemType.Separator:
+                return Separator;
+            case ListItemType.SectionHeader:
+                return Section;
+            default:
+                break;
         }
 
         return GridProperties switch

src/modules/cmdpal/Microsoft.CmdPal.UI/Converters/GridItemTemplateSelector.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using Microsoft.CmdPal.Core.ViewModels;
+using Microsoft.CommandPalette.Extensions.Toolkit;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 
@@ -24,15 +25,19 @@ internal sealed partial class GridItemTemplateSelector : DataTemplateSelector
 
     protected override DataTemplate? SelectTemplateCore(object item, DependencyObject dependencyObject)
     {
-        if (item is ListItemViewModel element && element.IsSectionOrSeparator)
+        if (item is not ListItemViewModel element)
         {
-            if (dependencyObject is UIElement li)
-            {
-                li.IsTabStop = false;
-                li.IsHitTestVisible = false;
-            }
+            return Medium;
+        }
 
-            return string.IsNullOrWhiteSpace(element.Section) ? Separator : Section;
+        switch (element.Type)
+        {
+            case ListItemType.Separator:
+                return Separator;
+            case ListItemType.SectionHeader:
+                return Section;
+            default:
+                break;
         }
 
         return GridProperties switch

src/modules/cmdpal/Microsoft.CmdPal.UI/Converters/ListItemContainerStyleSelector.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using Microsoft.CmdPal.Core.ViewModels;
+using Microsoft.CommandPalette.Extensions.Toolkit;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 
@@ -18,11 +19,20 @@ internal sealed partial class ListItemContainerStyleSelector : StyleSelector
 
     protected override Style? SelectStyleCore(object item, DependencyObject container)
     {
-        return item switch
+        if (item is not ListItemViewModel element)
         {
-            ListItemViewModel { IsSectionOrSeparator: true } listItemViewModel when string.IsNullOrWhiteSpace(listItemViewModel.Title) => Separator!,
-            ListItemViewModel { IsSectionOrSeparator: true } => Section,
-            _ => Default,
-        };
+            return Default;
+        }
+
+        switch (element.Type)
+        {
+            case ListItemType.Separator:
+                return Separator;
+            case ListItemType.SectionHeader:
+                return Section;
+            case ListItemType.Item:
+            default:
+                return Default;
+        }
     }
 }

src/modules/cmdpal/Microsoft.CmdPal.UI/Converters/ListItemTemplateSelector.cs

@@ -18,30 +18,20 @@ public sealed partial class ListItemTemplateSelector : DataTemplateSelector
 
     protected override DataTemplate? SelectTemplateCore(object item, DependencyObject container)
     {
-        DataTemplate? dataTemplate = ListItem;
-
-        if (container is ListViewItem listItem)
+        if (item is not ListItemViewModel element)
         {
-            if (item is ListItemViewModel element)
-            {
-                if (container is ListViewItem li && element.IsSectionOrSeparator)
-                {
-                    li.IsEnabled = false;
-                    li.AllowFocusWhenDisabled = false;
-                    li.AllowFocusOnInteraction = false;
-                    li.IsHitTestVisible = false;
-                    dataTemplate = string.IsNullOrWhiteSpace(element.Section) ? Separator : Section;
-                }
-                else
-                {
-                    listItem.IsEnabled = true;
-                    listItem.AllowFocusWhenDisabled = true;
-                    listItem.AllowFocusOnInteraction = true;
-                    listItem.IsHitTestVisible = true;
-                }
-            }
+            return ListItem;
         }
 
-        return dataTemplate;
+        switch (element.Type)
+        {
+            case ListItemType.Separator:
+                return Separator;
+            case ListItemType.SectionHeader:
+                return Section;
+            case ListItemType.Item:
+            default:
+                return ListItem;
+        }
     }
 }

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml

@@ -206,23 +206,30 @@
             x:Key="ListSectionContainerStyle"
             BasedOn="{StaticResource DefaultListViewItemStyle}"
             TargetType="ListViewItem">
+            <Setter Property="IsEnabled" Value="False" />
+            <Setter Property="AllowFocusWhenDisabled" Value="False" />
+            <Setter Property="AllowFocusOnInteraction" Value="False" />
             <Setter Property="IsHitTestVisible" Value="False" />
             <Setter Property="IsTabStop" Value="False" />
             <Setter Property="IsHoldingEnabled" Value="False" />
+            <Setter Property="AllowDrop" Value="False" />
             <Setter Property="Padding" Value="16,8,12,0" />
             <Setter Property="HorizontalContentAlignment" Value="Stretch" />
             <Setter Property="VerticalContentAlignment" Value="Bottom" />
             <Setter Property="MinHeight" Value="{StaticResource ListViewSectionMinHeight}" />
-            <Setter Property="AllowDrop" Value="False" />
         </Style>
 
         <Style
             x:Key="ListSeparatorContainerStyle"
             BasedOn="{StaticResource DefaultListViewItemStyle}"
             TargetType="ListViewItem">
+            <Setter Property="IsEnabled" Value="False" />
+            <Setter Property="AllowFocusWhenDisabled" Value="False" />
+            <Setter Property="AllowFocusOnInteraction" Value="False" />
             <Setter Property="IsHitTestVisible" Value="False" />
             <Setter Property="IsTabStop" Value="False" />
             <Setter Property="IsHoldingEnabled" Value="False" />
+            <Setter Property="AllowDrop" Value="False" />
             <Setter Property="Padding" Value="16,4,12,4" />
             <Setter Property="HorizontalContentAlignment" Value="Stretch" />
             <Setter Property="VerticalContentAlignment" Value="Center" />

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml.cs

@@ -1026,10 +1026,7 @@ public sealed partial class ListPage : Page,
         ItemView.SelectedIndex = newIndex;
     }
 
-    /// <summary>
-    ///  Code stealed from <see cref="Controls.ContextMenu.IsSeparator(object)"/>
-    /// </summary>
-    private bool IsSeparator(object? item) => item is ListItemViewModel li && li.IsSectionOrSeparator;
+    private bool IsSeparator(object? item) => item is ListItemViewModel li && !li.IsInteractive;
 
     private enum InputSource
     {