WIP: Use ItemsRepeater as base for ItemsPresenter

samples/ControlCatalog/Pages/ListBoxPage.xaml

@@ -10,8 +10,23 @@
               HorizontalAlignment="Center"
               Spacing="16">
       <StackPanel Orientation="Vertical" Spacing="8">
-        <ListBox Items="{Binding Items}" SelectedItem="{Binding SelectedItem}" AutoScrollToSelectedItem="True"  SelectedItems="{Binding SelectedItems}" SelectionMode="{Binding SelectionMode}" Width="250" Height="350"></ListBox>
+        <ListBox Items="{Binding Items}"
+                 Layout="{Binding Layout}"
+                 SelectedItem="{Binding SelectedItem}"
+                 AutoScrollToSelectedItem="True"
+                 SelectedItems="{Binding SelectedItems}"
+                 SelectionMode="{Binding SelectionMode}"
+                 ScrollViewer.VerticalScrollBarVisibility="{Binding VerticalScroll}"
+                 ScrollViewer.HorizontalScrollBarVisibility="{Binding HorizontalScroll}"
+                 Width="250" Height="350"/>
 
+        <ComboBox SelectedIndex="{Binding LayoutType}">
+          <ComboBoxItem>Stack - Vertical</ComboBoxItem>
+          <ComboBoxItem>Stack - Horizontal</ComboBoxItem>
+          <ComboBoxItem>UniformGrid - Vertical</ComboBoxItem>
+          <ComboBoxItem>UniformGrid - Horizontal</ComboBoxItem>
+        </ComboBox>
+
         <Button Command="{Binding AddItemCommand}">Add</Button>
 
         <Button Command="{Binding RemoveItemCommand}">Remove</Button>

samples/ControlCatalog/Pages/ListBoxPage.xaml.cs

@@ -4,6 +4,7 @@
 using System.Reactive;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
+using ControlCatalog.ViewModels;
 using ReactiveUI;
 
 namespace ControlCatalog.Pages
@@ -13,72 +14,12 @@ public class ListBoxPage : UserControl
         public ListBoxPage()
         {
             InitializeComponent();
-            DataContext = new PageViewModel();
+            DataContext = new ListBoxPageViewModel();
         }
 
         private void InitializeComponent()
         {
             AvaloniaXamlLoader.Load(this);
         }
-
-        private class PageViewModel : ReactiveObject
-        {
-            private int _counter;
-            private SelectionMode _selectionMode;
-
-            public PageViewModel()
-            {
-                Items = new ObservableCollection<string>(Enumerable.Range(1, 10000).Select(i => GenerateItem()));
-                SelectedItems = new ObservableCollection<string>();
-
-                AddItemCommand = ReactiveCommand.Create(() => Items.Add(GenerateItem()));
-
-                RemoveItemCommand = ReactiveCommand.Create(() =>
-                {
-                    while (SelectedItems.Count > 0)
-                    {
-                        Items.Remove(SelectedItems[0]);
-                    }
-                });
-
-                SelectRandomItemCommand = ReactiveCommand.Create(() =>
-                {
-                    var random = new Random();
-
-                    SelectedItem = Items[random.Next(Items.Count - 1)];
-                });
-            }
-
-            public ObservableCollection<string> Items { get; }
-
-            private string _selectedItem;
-
-            public string SelectedItem
-            {
-                get { return _selectedItem; }
-                set { this.RaiseAndSetIfChanged(ref _selectedItem, value); }
-            }
-
-
-            public ObservableCollection<string> SelectedItems { get; }
-
-            public ReactiveCommand<Unit, Unit> AddItemCommand { get; }
-
-            public ReactiveCommand<Unit, Unit> RemoveItemCommand { get; }
-
-            public ReactiveCommand<Unit, Unit> SelectRandomItemCommand { get; }
-
-            public SelectionMode SelectionMode
-            {
-                get => _selectionMode;
-                set
-                {
-                    SelectedItems.Clear();
-                    this.RaiseAndSetIfChanged(ref _selectionMode, value);
-                }
-            }
-
-            private string GenerateItem() => $"Item {_counter++.ToString()}";
-        }
     }
 }

samples/ControlCatalog/Pages/TreeViewPage.xaml

@@ -10,7 +10,12 @@
                 HorizontalAlignment="Center"
                 Spacing="16">
       <StackPanel Orientation="Vertical" Spacing="8">
-        <TreeView Items="{Binding Items}" SelectedItems="{Binding SelectedItems}" SelectionMode="{Binding SelectionMode}" Width="250" Height="350">
+        <TreeView Name="treeView"
+                  Items="{Binding Items}"
+                  SelectedItems="{Binding SelectedItems}"
+                  SelectionMode="{Binding SelectionMode}"
+                  Width="250"
+                  Height="350">
           <TreeView.ItemTemplate>
             <TreeDataTemplate ItemsSource="{Binding Children}">
               <TextBlock Text="{Binding Header}"/>
@@ -28,6 +33,7 @@
           <ComboBoxItem>Toggle</ComboBoxItem>
           <ComboBoxItem>AlwaysSelected</ComboBoxItem>
         </ComboBox>
+        <TextBlock Text="{Binding ContainerCount, StringFormat=\{0\} Containers Materialized}"/>
       </StackPanel>
     </StackPanel>
   </StackPanel>

samples/ControlCatalog/Pages/TreeViewPage.xaml.cs

@@ -1,115 +1,48 @@
-using System.Collections.ObjectModel;
+using System;
 using System.Linq;
-using System.Reactive;
+using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
-using ReactiveUI;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+using ControlCatalog.ViewModels;
 
 namespace ControlCatalog.Pages
 {
     public class TreeViewPage : UserControl
     {
+        private TreeView _treeView;
+        private DispatcherTimer _timer;
+
         public TreeViewPage()
         {
             InitializeComponent();
-            DataContext = new PageViewModel();
+            _treeView = this.FindControl<TreeView>("treeView");
+            _timer = new DispatcherTimer(TimeSpan.FromSeconds(1), DispatcherPriority.Background, TimerTick);
+            DataContext = new TreeViewPageViewModel();
         }
 
-        private void InitializeComponent()
+        protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
         {
-            AvaloniaXamlLoader.Load(this);
+            base.OnAttachedToVisualTree(e);
+            _timer.Start();
         }
 
-        private class PageViewModel : ReactiveObject
+        protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)
         {
-            private SelectionMode _selectionMode;
-
-            public PageViewModel()
-            {
-                Node root = new Node();
-                Items = root.Children;
-                SelectedItems = new ObservableCollection<Node>();
-
-                AddItemCommand = ReactiveCommand.Create(() =>
-                {
-                    Node parentItem = SelectedItems.Count > 0 ? SelectedItems[0] : root;
-                    parentItem.AddNewItem();
-                });
-
-                RemoveItemCommand = ReactiveCommand.Create(() =>
-                {
-                    while (SelectedItems.Count > 0)
-                    {
-                        Node lastItem = SelectedItems[0];
-                        RecursiveRemove(Items, lastItem);
-                        SelectedItems.Remove(lastItem);
-                    }
-
-                    bool RecursiveRemove(ObservableCollection<Node> items, Node selectedItem)
-                    {
-                        if (items.Remove(selectedItem))
-                        {
-                            return true;
-                        }
-
-                        foreach (Node item in items)
-                        {
-                            if (item.AreChildrenInitialized && RecursiveRemove(item.Children, selectedItem))
-                            {
-                                return true;
-                            }
-                        }
-
-                        return false;
-                    }
-                });
-            }
-
-            public ObservableCollection<Node> Items { get; }
-
-            public ObservableCollection<Node> SelectedItems { get; }
-
-            public ReactiveCommand<Unit, Unit> AddItemCommand { get; }
-
-            public ReactiveCommand<Unit, Unit> RemoveItemCommand { get; }
-
-            public SelectionMode SelectionMode
-            {
-                get => _selectionMode;
-                set
-                {
-                    SelectedItems.Clear();
-                    this.RaiseAndSetIfChanged(ref _selectionMode, value);
-                }
-            }
+            base.OnDetachedFromVisualTree(e);
+            _timer.Stop();
         }
 
-        private class Node
+        private void InitializeComponent()
         {
-            private int _counter;
-            private ObservableCollection<Node> _children;
-
-            public string Header { get; private set; }
-
-            public bool AreChildrenInitialized => _children != null;
-
-            public ObservableCollection<Node> Children
-            {
-                get
-                {
-                    if (_children == null)
-                    {
-                        _children = new ObservableCollection<Node>(Enumerable.Range(1, 10).Select(i => CreateNewNode()));
-                    }
-                    return _children;
-                }
-            }
-
-            public void AddNewItem() => Children.Add(CreateNewNode());
-
-            public override string ToString() => Header;
+            AvaloniaXamlLoader.Load(this);
+        }
 
-            private Node CreateNewNode() => new Node {Header = $"Item {_counter++}"};
+        private void TimerTick(object sender, EventArgs e)
+        {
+            var vm = (TreeViewPageViewModel)DataContext;
+            vm.ContainerCount = _treeView.GetVisualDescendants().OfType<TreeViewItem>().Count();
         }
     }
 }

samples/ControlCatalog/ViewModels/ListBoxPageViewModel.cs

@@ -0,0 +1,124 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Reactive;
+using System.Reactive.Linq;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Layout;
+using ReactiveUI;
+
+namespace ControlCatalog.ViewModels
+{
+    public enum LayoutType
+    {
+        StackVertical,
+        StackHorizontal,
+        UniformGridHorizontal,
+        UniformGridVertical,
+    }
+
+    public class ListBoxPageViewModel :ReactiveObject
+    {
+        private readonly ObservableAsPropertyHelper<AttachedLayout> _layout;
+        private readonly ObservableAsPropertyHelper<ScrollBarVisibility> _horizontalScroll;
+        private readonly ObservableAsPropertyHelper<ScrollBarVisibility> _verticalScroll;
+        private int _counter;
+        private LayoutType _layoutType;
+        private SelectionMode _selectionMode;
+        private string _selectedItem;
+
+        public ListBoxPageViewModel()
+        {
+            Items = new ObservableCollection<string>(Enumerable.Range(1, 10000).Select(i => GenerateItem()));
+            SelectedItems = new ObservableCollection<string>();
+
+            _layout = this.WhenAnyValue(x => x.LayoutType)
+                .Select(CreateLayout)
+                .ToProperty(this, x => x.Layout);
+
+            _horizontalScroll = this.WhenAnyValue(x => x.LayoutType)
+                .Select(x => (((int)x) % 2) == 0 ? ScrollBarVisibility.Disabled : ScrollBarVisibility.Auto)
+                .ToProperty(this, x => x.HorizontalScroll);
+
+            _verticalScroll = this.WhenAnyValue(x => x.LayoutType)
+                .Select(x => (((int)x) % 2) != 0 ? ScrollBarVisibility.Disabled : ScrollBarVisibility.Auto)
+                .ToProperty(this, x => x.VerticalScroll);
+
+            AddItemCommand = ReactiveCommand.Create(() => Items.Add(GenerateItem()));
+
+            RemoveItemCommand = ReactiveCommand.Create(() =>
+            {
+                while (SelectedItems.Count > 0)
+                {
+                    Items.Remove(SelectedItems[0]);
+                }
+            });
+
+            SelectRandomItemCommand = ReactiveCommand.Create(() =>
+            {
+                var random = new Random();
+
+                SelectedItem = Items[random.Next(Items.Count - 1)];
+            });
+        }
+
+        public ObservableCollection<string> Items { get; }
+        public AttachedLayout Layout => _layout.Value;
+        public ScrollBarVisibility HorizontalScroll => _horizontalScroll.Value;
+        public ScrollBarVisibility VerticalScroll => _verticalScroll.Value;
+        public ObservableCollection<string> SelectedItems { get; }
+        public ReactiveCommand<Unit, Unit> AddItemCommand { get; }
+        public ReactiveCommand<Unit, Unit> RemoveItemCommand { get; }
+        public ReactiveCommand<Unit, Unit> SelectRandomItemCommand { get; }
+
+        public LayoutType LayoutType
+        {
+            get => _layoutType;
+            set => this.RaiseAndSetIfChanged(ref _layoutType, value);
+        }
+
+        public string SelectedItem
+        {
+            get => _selectedItem;
+            set => this.RaiseAndSetIfChanged(ref _selectedItem, value);
+        }
+
+        public SelectionMode SelectionMode
+        {
+            get => _selectionMode;
+            set
+            {
+                SelectedItems.Clear();
+                this.RaiseAndSetIfChanged(ref _selectionMode, value);
+            }
+        }
+
+        private string GenerateItem() => $"Item {_counter++.ToString()}";
+
+        private static AttachedLayout CreateLayout(LayoutType type)
+        {
+            switch (type)
+            {
+                case LayoutType.StackVertical:
+                    return new StackLayout { Orientation = Orientation.Vertical };
+                case LayoutType.StackHorizontal:
+                    return new StackLayout { Orientation = Orientation.Horizontal };
+                case LayoutType.UniformGridVertical:
+                    return new UniformGridLayout 
+                    {
+                        MinItemWidth = 70,
+                        Orientation = Orientation.Vertical 
+                    };
+                case LayoutType.UniformGridHorizontal:
+                    return new UniformGridLayout 
+                    {
+                        MinItemWidth = 70,
+                        Orientation = Orientation.Horizontal 
+                    };
+                default:
+                    throw new NotSupportedException();
+            }
+        }
+    }
+}