Better workaround for ItemsRepeater

ModernWpf.Controls/NavigationView/NavigationView.cs

@@ -472,7 +472,6 @@ public override void OnApplyTemplate()
                 m_leftNavRepeaterGettingFocusHelper.GettingFocus += OnRepeaterGettingFocus;
 
                 leftNavRepeater.ItemTemplate = m_navigationViewItemsFactory;
-                leftNavRepeater.AlwaysInvalidateMeasureOnChildDesiredSizeChanged = true;
             }
 
             // Change code to NOT do this if we're in left nav mode, to prevent it from being realized:
@@ -496,7 +495,6 @@ public override void OnApplyTemplate()
                 m_topNavRepeaterGettingFocusHelper.GettingFocus += OnRepeaterGettingFocus;
 
                 topNavRepeater.ItemTemplate = m_navigationViewItemsFactory;
-                topNavRepeater.AlwaysInvalidateMeasureOnChildDesiredSizeChanged = true;
             }
 
             // Change code to NOT do this if we're in left nav mode, to prevent it from being realized:
@@ -516,7 +514,6 @@ public override void OnApplyTemplate()
                 topNavListOverflowRepeater.ElementClearing += OnRepeaterElementClearing;
 
                 topNavListOverflowRepeater.ItemTemplate = m_navigationViewItemsFactory;
-                topNavListOverflowRepeater.AlwaysInvalidateMeasureOnChildDesiredSizeChanged = true;
             }
 
             if (GetTemplateChild(c_topNavOverflowButton) is Button topNavOverflowButton)

ModernWpf.Controls/NavigationView/NavigationViewItem.cs

@@ -125,7 +125,6 @@ public override void OnApplyTemplate()
                     m_repeaterElementClearingRevoker = new ItemsRepeaterElementClearingRevoker(repeater, nvImpl.OnRepeaterElementClearing);
 
                     repeater.ItemTemplate = nvImpl.GetNavigationViewItemsFactory();
-                    repeater.AlwaysInvalidateMeasureOnChildDesiredSizeChanged = true;
                 }
 
                 UpdateRepeaterItemsSource();

ModernWpf.Controls/Repeater/ItemsRepeater/ItemsRepeater.cs

@@ -111,7 +111,6 @@ protected override Size MeasureOverride(Size availableSize)
 
                 m_viewportManager.SetLayoutExtent(extent);
                 m_lastAvailableSize = availableSize;
-                OnLayoutEvent(LayoutEvent.Measure);
                 return desiredSize;
             }
             finally
@@ -175,14 +174,13 @@ protected override Size ArrangeOverride(Size finalSize)
                         }
 
                         virtInfo.ArrangeBounds = newBounds;
+                        virtInfo.DesiredSize = element.DesiredSize;
                     }
                 }
 
                 m_viewportManager.OnOwnerArranged();
                 AnimationManager.OnOwnerArranged();
 
-                OnLayoutEvent(LayoutEvent.Arrange);
-
                 return arrangeSize;
             }
             finally

ModernWpf.Controls/Repeater/ItemsRepeater/ItemsRepeater.wpf.cs

@@ -1,85 +1,34 @@
-using System.Collections.Generic;
-using System.Windows;
+using System.Windows;
 using System.Windows.Controls;
 
 namespace ModernWpf.Controls
 {
     partial class ItemsRepeater
     {
-        internal bool AlwaysInvalidateMeasureOnChildDesiredSizeChanged { get; set; }
-
+        // WPF-specific workaround to avoid freezing and improve performance
         protected override void OnChildDesiredSizeChanged(UIElement child)
         {
-            if (AlwaysInvalidateMeasureOnChildDesiredSizeChanged)
+            var virtInfo = TryGetVirtualizationInfo(child);
+            if (virtInfo != null && virtInfo.IsRealized)
             {
-                base.OnChildDesiredSizeChanged(child);
-                return;
-            }
-
-            bool ignore = true;
-
-            var last = m_layoutEvents.Last;
-            if (last != null)
-            {
-                if (last.Value == LayoutEvent.Measure)
-                {
-                    if (last.Previous?.Value != LayoutEvent.Measure)
-                    {
-                        ignore = false;
-                    }
-                }
-                else if (last.Value == LayoutEvent.Arrange)
+                var oldDesiredSize = virtInfo.DesiredSize;
+                if (!oldDesiredSize.IsEmpty)
                 {
-                    var previous = last.Previous;
-                    if (previous == null || previous.Value == LayoutEvent.Measure)
+                    var newDesiredSize = child.DesiredSize;
+                    var renderSize = child.RenderSize;
+
+                    if (newDesiredSize.Height != oldDesiredSize.Height && renderSize.Height == oldDesiredSize.Height ||
+                        newDesiredSize.Width != oldDesiredSize.Width && renderSize.Width == oldDesiredSize.Width)
                     {
-                        var virtInfo = GetVirtualizationInfo(child);
-                        if (virtInfo.IsPinned)
-                        {
-                            ignore = false;
-                        }
+                        base.OnChildDesiredSizeChanged(child);
                     }
                 }
             }
-            else
-            {
-                ignore = false;
-            }
-
-            if (!ignore)
-            {
-                OnLayoutEvent(LayoutEvent.ChildDesiredSizeChanged);
-                base.OnChildDesiredSizeChanged(child);
-            }
         }
 
         protected override UIElementCollection CreateUIElementCollection(FrameworkElement logicalParent)
         {
             return new RepeaterUIElementCollection(this, logicalParent);
         }
-
-        private void OnLayoutEvent(LayoutEvent e)
-        {
-            if (AlwaysInvalidateMeasureOnChildDesiredSizeChanged)
-            {
-                return;
-            }
-
-            if (m_layoutEvents.Count >= 2)
-            {
-                m_layoutEvents.RemoveFirst();
-            }
-
-            m_layoutEvents.AddLast(e);
-        }
-
-        private enum LayoutEvent
-        {
-            Measure,
-            Arrange,
-            ChildDesiredSizeChanged
-        }
-
-        private readonly LinkedList<LayoutEvent> m_layoutEvents = new LinkedList<LayoutEvent>();
     }
 }

ModernWpf.Controls/Repeater/Layouts/VirtualizationInfo.cs

@@ -147,6 +147,8 @@ public void UpdateIndex(int newIndex)
 
         public bool AutoRecycleCandidate { get; set; } = false;
 
+        public Size DesiredSize { get; set; } = Size.Empty;
+
         private uint m_pinCounter = 0u;
     }
 }

ModernWpf.SampleApp/ControlPages/ItemsRepeaterPage.xaml

@@ -191,7 +191,7 @@
                 <TextBlock
                     Grid.Column="1"
                     Grid.Row="1"
-                    Text="{Binding Company, Mode=OneTime}"
+                    Text="{Binding Company}"
                     Style="{StaticResource BodyTextBlockStyle}"
                     Margin="12,0,0,6" />
             </Grid>
@@ -361,6 +361,10 @@
                             x:Name="changeFirstItemButton"
                             Content="Change first item"
                             Click="ChangeFirstItemButton_Click" />
+                        <Button
+                            x:Name="modifyFirstItemButton"
+                            Content="Modify first item"
+                            Click="ModifyFirstItemButton_Click" />
                     </ui:SimpleStackPanel>
                 </sc:ControlExample.Options>
             </sc:ControlExample>

ModernWpf.SampleApp/ControlPages/ItemsRepeaterPage.xaml.cs

@@ -192,6 +192,20 @@ private void ChangeFirstItemButton_Click(object sender, RoutedEventArgs e)
             var contacts = (ObservableCollection<Contact>)DataContext;
             contacts[0] = new Contact("First", "Last", "Line 1\nLine 2");
         }
+
+        private void ModifyFirstItemButton_Click(object sender, RoutedEventArgs e)
+        {
+            var contacts = (ObservableCollection<Contact>)DataContext;
+            var firstContact = contacts[0];
+            if (firstContact.Company.Contains("\n"))
+            {
+                firstContact.ChangeCompany("Line 1");
+            }
+            else
+            {
+                firstContact.ChangeCompany("Line 1\nLine 2");
+            }
+        }
     }
 
     public class NestedCategory

ModernWpf.SampleApp/ControlPages/ListViewPage.xaml.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.ComponentModel;
 using System.Globalization;
 using System.IO;
 using System.Linq;
@@ -24,7 +25,7 @@ private async void OnLoaded(object sender, RoutedEventArgs e)
         }
     }
 
-    public class Contact
+    public class Contact : INotifyPropertyChanged
     {
         #region Properties
         public string FirstName { get; private set; }
@@ -40,6 +41,8 @@ public Contact(string firstName, string lastName, string company)
             Company = company;
         }
 
+        public event PropertyChangedEventHandler PropertyChanged;
+
         #region Public Methods
         public static Task<ObservableCollection<Contact>> GetContactsAsync()
         {
@@ -77,6 +80,12 @@ public override string ToString()
         {
             return Name;
         }
+
+        public void ChangeCompany(string company)
+        {
+            Company = company;
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Company)));
+        }
         #endregion
     }