Add ResourceListTreeViewItem with special handling for null items

UndertaleModTool/Controls/ResourceListTreeViewItem.xaml

@@ -0,0 +1,49 @@
+<TreeViewItem x:Class="UndertaleModTool.ResourceListTreeViewItem"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+             xmlns:local="clr-namespace:UndertaleModTool"
+             xmlns:undertalelib="clr-namespace:UndertaleModLib;assembly=UndertaleModLib"
+             mc:Ignorable="d">
+
+    <TreeViewItem.Resources>
+        <local:ImplementsInterfaceConverter x:Key="ImplementsInterfaceConverter"/>
+
+        <DataTemplate x:Key="NullResourceItemTemplate">
+            <TextBlock Text="(null)"/>
+        </DataTemplate>
+
+        <local:ContextMenuDark x:Key="UndertaleResourceMenu" Opened="MenuItem_ContextMenuOpened">
+            <MenuItem Header="Open in new tab" Click="MenuItem_OpenInNewTab_Click"/>
+            <MenuItem Header="Find all references" Click="MenuItem_FindAllReferences_Click"/>
+            <MenuItem Header="Copy name to clipboard" Click="MenuItem_CopyName_Click"/>
+            <MenuItem Header="Delete" Click="MenuItem_Delete_Click"/>
+        </local:ContextMenuDark>
+
+        <!-- TODO: Would need some way to know the ID, IndexOf won't be reliable
+        <local:ContextMenuDark x:Key="NullResourceItemReplaceMenu" Opened="MenuItem_ContextMenuOpened_NullItem">
+            <MenuItem IsEnabled="False" Header="ID: " Name="ObjectIdLabel" />
+            <Separator />
+            <MenuItem Header="_Add in place" />
+        </local:ContextMenuDark>
+        -->
+
+        <Style x:Key="ResourceListTreeViewItem.ItemContainerStyle" TargetType="{x:Type TreeViewItem}">
+            <Style.Triggers>
+                <DataTrigger Binding="{Binding ., Converter={StaticResource ImplementsInterfaceConverter}, ConverterParameter={x:Type undertalelib:UndertaleResource}}" Value="True">
+                    <Setter Property="ContextMenu" Value="{StaticResource UndertaleResourceMenu}"/>
+                </DataTrigger>
+                <DataTrigger Binding="{Binding .}" Value="{x:Null}">
+                    <Setter Property="Foreground" Value="Gray"/>
+                    <!--<Setter Property="ContextMenu" Value="{StaticResource NullResourceItemReplaceMenu}"/>-->
+                </DataTrigger>
+            </Style.Triggers>
+        </Style>
+    </TreeViewItem.Resources>
+
+    <TreeViewItem.ItemContainerStyle>
+        <StaticResource ResourceKey="ResourceListTreeViewItem.ItemContainerStyle"/>
+    </TreeViewItem.ItemContainerStyle>
+
+</TreeViewItem>

UndertaleModTool/Controls/ResourceListTreeViewItem.xaml.cs

@@ -0,0 +1,127 @@
+using System;
+using System.Collections.Generic;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using UndertaleModLib;
+using UndertaleModTool.Windows;
+
+namespace UndertaleModTool
+{
+    public partial class ResourceListTreeViewItem : TreeViewItem
+    {
+        public static readonly DependencyProperty DefaultTemplateProperty = DependencyProperty.Register(
+            "DefaultTemplate", typeof(DataTemplate), typeof(ResourceListTreeViewItem),
+            new FrameworkPropertyMetadata(default(DataTemplate), FrameworkPropertyMetadataOptions.AffectsRender, OnDefaultTemplateChanged));
+
+        public DataTemplate DefaultTemplate
+        {
+            get { return (DataTemplate)GetValue(DefaultTemplateProperty); }
+            set { SetValue(DefaultTemplateProperty, value); }
+        }
+
+        public ResourceListTreeViewItem()
+        {
+            InitializeComponent();
+
+            Binding visibilityBinding = new("ItemsSource")
+            {
+                Converter = new NullToVisibilityConverter() {
+                    nullValue = Visibility.Collapsed,
+                    notNullValue = Visibility.Visible
+                },
+                RelativeSource = RelativeSource.Self,
+                UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
+            };
+            SetBinding(VisibilityProperty, visibilityBinding);
+
+            ItemTemplateSelector = new ResourceItemTemplateSelector()
+            {
+                DefaultTemplate = DefaultTemplate,
+                NullTemplate = FindResource("NullResourceItemTemplate") as DataTemplate
+            };
+        }
+
+        private static void OnDefaultTemplateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            ResourceListTreeViewItem item = d as ResourceListTreeViewItem;
+            if (item is not null)
+                (item.ItemTemplateSelector as ResourceItemTemplateSelector).DefaultTemplate = item.DefaultTemplate;
+        }
+
+        private void MenuItem_ContextMenuOpened(object sender, RoutedEventArgs e)
+        {
+            var menu = sender as ContextMenu;
+            foreach (var item in menu.Items)
+            {
+                var menuItem = item as MenuItem;
+                if ((menuItem.Header as string) == "Find all references")
+                {
+                    menuItem.Visibility = UndertaleResourceReferenceMap.IsTypeReferenceable(menu.DataContext?.GetType())
+                                          ? Visibility.Visible : Visibility.Collapsed;
+
+                    break;
+                }
+            }
+        }
+
+        private void MenuItem_OpenInNewTab_Click(object sender, RoutedEventArgs e)
+        {
+            MainWindow window = (MainWindow)Application.Current.MainWindow;
+            window.OpenInTab(window.Highlighted, true);
+        }
+
+        private void MenuItem_FindAllReferences_Click(object sender, RoutedEventArgs e)
+        {
+            MainWindow window = (MainWindow)Application.Current.MainWindow;
+            var obj = (sender as FrameworkElement)?.DataContext as UndertaleResource;
+            if (obj is null)
+            {
+                window.ShowError("The selected object is not an \"UndertaleResource\".");
+                return;
+            }
+
+            FindReferencesTypesDialog dialog = null;
+            try
+            {
+                dialog = new(obj, window.Data);
+                dialog.ShowDialog();
+            }
+            catch (Exception ex)
+            {
+                window.ShowError("An error occured in the object references related window.\n" +
+                               $"Please report this on GitHub.\n\n{ex}");
+            }
+            finally
+            {
+                dialog?.Close();
+            }
+        }
+
+        private void MenuItem_CopyName_Click(object sender, RoutedEventArgs e)
+        {
+            MainWindow window = (MainWindow)Application.Current.MainWindow;
+            window.CopyItemName(window.Highlighted);
+        }
+
+        private void MenuItem_Delete_Click(object sender, RoutedEventArgs e)
+        {
+            MainWindow window = (MainWindow)Application.Current.MainWindow;
+            if (window.Highlighted is UndertaleObject obj)
+                window.DeleteItem(obj);
+        }
+    }
+
+    public class ResourceItemTemplateSelector : DataTemplateSelector
+    {
+        public DataTemplate DefaultTemplate { get; set; }
+        public DataTemplate NullTemplate { get; set; }
+
+        public override DataTemplate SelectTemplate(object item, DependencyObject container)
+        {
+            if (item is null)
+                return NullTemplate;
+            return DefaultTemplate;
+        }
+    }
+}