Added a search bar to limit large XSD files

XSDVisualiser.Desktop/MainWindow.axaml

@@ -16,6 +16,22 @@
         <!-- Header -->
         <DockPanel LastChildFill="False">
             <TextBlock Text="XSD Visualiser" FontSize="20" FontWeight="SemiBold" Margin="0,0,12,0" DockPanel.Dock="Left"/>
+            
+            <!-- Searchable dropdown for root elements -->
+            <AutoCompleteBox Width="320" Margin="0,0,12,0" Watermark="Search and choose a root element"
+                              ItemsSource="{Binding RootElements}"
+                              FilterMode="Contains"
+                              MinimumPrefixLength="0">
+                <AutoCompleteBox.ItemTemplate>
+                    <DataTemplate>
+                        <TextBlock Text="{Binding .}"/>
+                    </DataTemplate>
+                </AutoCompleteBox.ItemTemplate>
+                <AutoCompleteBox.SelectedItem>
+                    <Binding Path="SelectedRootElement" Mode="TwoWay"/>
+                </AutoCompleteBox.SelectedItem>
+            </AutoCompleteBox>
+            
             <Button Content="Open XSD and parse" x:Name="OpenBtn" Width="220"/>
         </DockPanel>
 
@@ -26,7 +42,7 @@
                     BorderBrush="{DynamicResource PanelBorderBrush}"
                     BorderThickness="1" CornerRadius="6" Margin="0,8,8,0">
                 <ScrollViewer>
-                    <TreeView x:Name="SchemaTree" ItemsSource="{Binding RootElements}">
+                    <TreeView x:Name="SchemaTree" ItemsSource="{Binding VisibleRootElements}">
                         <TreeView.DataTemplates>
                             <TreeDataTemplate DataType="{x:Type m:SchemaNode}" ItemsSource="{Binding Children}">
                                 <StackPanel>

XSDVisualiser.Desktop/MainWindow.axaml.cs

@@ -5,6 +5,7 @@ using Avalonia.Interactivity;
 using Avalonia.Threading;
 using XSDVisualiser.Core;
 using XSDVisualiser.Models;
+using XSDVisualiser.Desktop.ViewModels;
 
 namespace XSDVisualiser.Desktop
 {
@@ -42,11 +43,11 @@ namespace XSDVisualiser.Desktop
                 {
                     var parser = new XsdSchemaParser();
                     var model = parser.Parse(path);
-                    Dispatcher.UIThread.Post(() => DataContext = model);
+                    Dispatcher.UIThread.Post(() => DataContext = new MainWindowViewModel(model));
                 }
                 catch (Exception ex)
                 {
-                    Dispatcher.UIThread.Post(() => DataContext = new SchemaModel { TargetNamespace = ex.Message });
+                    Dispatcher.UIThread.Post(() => DataContext = new MainWindowViewModel(new SchemaModel { TargetNamespace = ex.Message }));
                 }
             });
         }

XSDVisualiser.Desktop/ViewModels/MainWindowViewModel.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using XSDVisualiser.Models;
+
+namespace XSDVisualiser.Desktop.ViewModels
+{
+    public class MainWindowViewModel : INotifyPropertyChanged
+    {
+        private SchemaModel _model;
+        private SchemaNode? _selectedRootElement;
+
+        public MainWindowViewModel(SchemaModel model)
+        {
+            _model = model ?? throw new ArgumentNullException(nameof(model));
+        }
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        private void OnPropertyChanged([CallerMemberName] string? name = null)
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
+        }
+
+        public SchemaModel Model
+        {
+            get => _model;
+            set
+            {
+                if (!ReferenceEquals(_model, value))
+                {
+                    _model = value ?? throw new ArgumentNullException(nameof(value));
+                    OnPropertyChanged();
+                    OnPropertyChanged(nameof(RootElements));
+                    OnPropertyChanged(nameof(VisibleRootElements));
+                }
+            }
+        }
+
+        public IEnumerable<SchemaNode> RootElements => _model?.RootElements ?? Enumerable.Empty<SchemaNode>();
+
+        public SchemaNode? SelectedRootElement
+        {
+            get => _selectedRootElement;
+            set
+            {
+                if (!EqualityComparer<SchemaNode?>.Default.Equals(_selectedRootElement, value))
+                {
+                    _selectedRootElement = value;
+                    OnPropertyChanged();
+                    OnPropertyChanged(nameof(VisibleRootElements));
+                }
+            }
+        }
+
+        public IEnumerable<SchemaNode> VisibleRootElements
+        {
+            get
+            {
+                if (SelectedRootElement != null)
+                    return new[] { SelectedRootElement };
+                return RootElements;
+            }
+        }
+    }
+}

XSDVisualiser/Models/XsdSchemaModel.cs

@@ -54,6 +54,17 @@ namespace XSDVisualiser.Models
 
         [XmlAttribute]
         public string? ContentModel { get; set; } // sequence | choice | all | simple
+
+        public override string ToString()
+        {
+            // Used by AutoCompleteBox to get text for filtering and matching
+            // Prefer Name, then TypeName, and fall back to base implementation
+            if (!string.IsNullOrEmpty(Name))
+                return Name!;
+            if (!string.IsNullOrEmpty(TypeName))
+                return TypeName!;
+            return base.ToString();
+        }
     }
 
     /// <summary>