Set up a control that's essentially the same as ngIf in Angular.

FinModelUtility/UniversalAssetTool/UniversalAssetTool.Ui.Avalonia/common/controls/If.cs

@@ -0,0 +1,69 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Layout;
+using Avalonia.Markup.Xaml.Templates;
+using Avalonia.Metadata;
+
+namespace uni.ui.avalonia.common.controls;
+
+public class If : Control {
+  private object deferredContent_;
+  private Control control_;
+
+  public static readonly StyledProperty<bool> ConditionProperty
+      = AvaloniaProperty.Register<If, bool>(
+          "Condition");
+
+  public bool Condition {
+    get => this.GetValue(ConditionProperty);
+    set => this.SetValue(ConditionProperty, value);
+  }
+
+  [Content, TemplateContent]
+  public object DeferredContent {
+    get => this.deferredContent_;
+    set {
+      this.deferredContent_ = value;
+      if (this.Condition) {
+        this.DoLoad_(true);
+      }
+    }
+  }
+
+  public Control Control => this.control_;
+
+  static If() {
+    ConditionProperty.Changed.AddClassHandler<If>(
+        (c, e) => {
+          if (e.NewValue is bool v) {
+            c.DoLoad_(v);
+          }
+        });
+  }
+
+  protected override Size MeasureOverride(Size availableSize)
+    => LayoutHelper.MeasureChild(this.control_, availableSize, default);
+
+  protected override Size ArrangeOverride(Size finalSize)
+    => LayoutHelper.ArrangeChild(this.control_, finalSize, default);
+
+
+  private void DoLoad_(bool load) {
+    if ((this.control_ != null) == load)
+      return;
+
+    if (load) {
+      this.control_ = TemplateContent.Load(this.DeferredContent).Result;
+      ((ISetLogicalParent) this.control_).SetParent(this);
+      this.VisualChildren.Add(this.control_);
+      this.LogicalChildren.Add(this.control_);
+    } else {
+      ((ISetLogicalParent) this.control_).SetParent(null);
+      this.LogicalChildren.Clear();
+      this.VisualChildren.Remove(this.control_);
+      this.control_ = null;
+    }
+
+    this.InvalidateMeasure();
+  }
+}

FinModelUtility/UniversalAssetTool/UniversalAssetTool.Ui.Avalonia/common/treeViews/FileBundleTreeViewModels.cs

@@ -0,0 +1,86 @@
+using System;
+using System.Collections.ObjectModel;
+
+using fin.audio.io;
+using fin.audio.io.importers.ogg;
+using fin.image;
+using fin.io;
+using fin.io.bundles;
+using fin.model.io;
+using fin.scene;
+using fin.util.asserts;
+
+using grezzo.api;
+
+using uni.ui.avalonia.resources;
+using uni.ui.avalonia.ViewModels;
+
+using IImage = Avalonia.Media.IImage;
+
+namespace uni.ui.avalonia.common.treeViews {
+
+  // Top-level view model types
+  public class FileBundleTreeViewModel<T>
+      : ViewModelBase, IFilterTreeViewViewModel<T> {
+    public ObservableCollection<INode<T>> Nodes { get; protected set; }
+
+    public event EventHandler<INode<T>>? NodeSelected;
+
+    public void ChangeSelection(INode node)
+      => this.NodeSelected?.Invoke(this, Asserts.AsA<INode<T>>(node));
+  }
+
+  public class FileBundleTreeViewModel : FileBundleTreeViewModel<IAnnotatedFileBundle> {
+    public FileBundleTreeViewModel() {
+      this.Nodes = [
+          new FileBundleDirectoryNode("Animals",
+          [
+              new FileBundleDirectoryNode("Mammals",
+              [
+                  new FileBundleLeafNode("Lion", new CmbModelFileBundle("foo", new FinFile()).Annotate(null)),
+                  new FileBundleLeafNode("Cat", new OggAudioFileBundle(new FinFile()).Annotate(null))
+              ])
+          ])
+      ];
+    }
+  }
+
+  // Node types
+  public class FileBundleDirectoryNode(
+      string label,
+      ObservableCollection<INode<IAnnotatedFileBundle>>? subNodes = null)
+      : ViewModelBase, INode<IAnnotatedFileBundle> {
+    public ObservableCollection<INode<IAnnotatedFileBundle>>? SubNodes { get; }
+      = subNodes;
+
+    public IImage? Icon => null;
+
+    public string Label { get; } = label;
+  }
+
+  public class FileBundleLeafNode(string label, IAnnotatedFileBundle data)
+      : ViewModelBase, INode<IAnnotatedFileBundle> {
+    public ObservableCollection<INode<IAnnotatedFileBundle>>? SubNodes => null;
+
+    public static readonly IImage MUSIC_ICON
+        = EmbeddedResourceUtil.LoadAvaloniaImage("music");
+
+    public static readonly IImage PICTURE_ICON
+        = EmbeddedResourceUtil.LoadAvaloniaImage("picture");
+
+    public static readonly IImage MODEL_ICON
+        = EmbeddedResourceUtil.LoadAvaloniaImage("model");
+
+    public static readonly IImage SCENE_ICON
+        = EmbeddedResourceUtil.LoadAvaloniaImage("scene");
+
+    public IImage Icon => data.FileBundle switch {
+      IAudioFileBundle => MUSIC_ICON,
+      IImageFileBundle => PICTURE_ICON,
+      IModelFileBundle => MODEL_ICON,
+      ISceneFileBundle => SCENE_ICON,
+    };
+
+    public string Label { get; } = label;
+  }
+}

FinModelUtility/UniversalAssetTool/UniversalAssetTool.Ui.Avalonia/common/treeViews/FilterTreeView.axaml

@@ -4,6 +4,8 @@
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
              xmlns:textboxes="clr-namespace:uni.ui.avalonia.common.textboxes"
              xmlns:treeViews="clr-namespace:uni.ui.avalonia.common.treeViews"
+             xmlns:global="clr-namespace:"
+             xmlns:controls="clr-namespace:uni.ui.avalonia.common.controls"
              mc:Ignorable="d" d:DesignWidth="300" d:DesignHeight="450"
              x:Class="uni.ui.avalonia.common.treeViews.FilterTreeView"
              x:DataType="treeViews:FileBundleTreeViewModel">
@@ -45,11 +47,12 @@
       <TreeView.ItemTemplate>
         <TreeDataTemplate ItemsSource="{Binding SubNodes}">
           <StackPanel Orientation="Horizontal">
-            <Image IsVisible="{Binding Icon, Converter={x:Static ObjectConverters.IsNotNull}}"
-                   Source="{Binding Icon}" 
-                   Margin="-24 0 4 0"
-                   Height="16"
-                   Width="16" />
+            <controls:If Condition="{Binding Icon, Converter={x:Static ObjectConverters.IsNotNull}}">
+              <Image Source="{Binding Icon}"
+                     Margin="-24 0 4 0"
+                     Height="16"
+                     Width="16" />
+            </controls:If>
             <TextBlock Text="{Binding Label}" />
           </StackPanel>
         </TreeDataTemplate>

FinModelUtility/UniversalAssetTool/UniversalAssetTool.Ui.Avalonia/common/treeViews/FilterTreeView.axaml.cs

@@ -43,69 +43,4 @@ private void TreeView_OnSelectionChanged_(
       filterTreeViewViewModel.ChangeSelection(selectedNode);
     }
   }
-
-  // Top-level view model types
-  public class FileBundleTreeViewModel<T>
-      : ViewModelBase, IFilterTreeViewViewModel<T> {
-    public ObservableCollection<INode<T>> Nodes { get; protected set; }
-
-    public event EventHandler<INode<T>>? NodeSelected;
-
-    public void ChangeSelection(INode node)
-      => this.NodeSelected?.Invoke(this, Asserts.AsA<INode<T>>(node));
-  }
-
-  public class FileBundleTreeViewModel : FileBundleTreeViewModel<IAnnotatedFileBundle> {
-    public FileBundleTreeViewModel() {
-      this.Nodes = [
-          new ParentNode("Animals",
-          [
-              new ParentNode("Mammals",
-              [
-                  new LeafNode("Lion", new CmbModelFileBundle("foo", new FinFile()).Annotate(null)),
-                  new LeafNode("Cat", new OggAudioFileBundle(new FinFile()).Annotate(null))
-              ])
-          ])
-      ];
-    }
-  }
-
-  // Node types
-  public class ParentNode(
-      string label,
-      ObservableCollection<INode<IAnnotatedFileBundle>>? subNodes = null)
-      : ViewModelBase, INode<IAnnotatedFileBundle> {
-    public ObservableCollection<INode<IAnnotatedFileBundle>>? SubNodes { get; }
-      = subNodes;
-
-    public IImage? Icon => null;
-
-    public string Label { get; } = label;
-  }
-
-  public class LeafNode(string label, IAnnotatedFileBundle data)
-      : ViewModelBase, INode<IAnnotatedFileBundle> {
-    public ObservableCollection<INode<IAnnotatedFileBundle>>? SubNodes => null;
-
-    public static readonly IImage MUSIC_ICON
-        = EmbeddedResourceUtil.LoadAvaloniaImage("music");
-
-    public static readonly IImage PICTURE_ICON
-        = EmbeddedResourceUtil.LoadAvaloniaImage("picture");
-
-    public static readonly IImage MODEL_ICON
-        = EmbeddedResourceUtil.LoadAvaloniaImage("model");
-
-    public static readonly IImage SCENE_ICON
-        = EmbeddedResourceUtil.LoadAvaloniaImage("scene");
-
-    public IImage? Icon => data.FileBundle switch {
-        IAudioFileBundle => MUSIC_ICON,
-        IImageFileBundle => PICTURE_ICON,
-        IModelFileBundle => MODEL_ICON,
-        ISceneFileBundle => SCENE_ICON,
-    };
-
-    public string Label { get; } = label;
-  }
 }