Merge pull request #710 from AvaloniaUI/fix-virtualization

Fix virtualization

src/Avalonia.Controls/IVirtualizingPanel.cs

@@ -1,6 +1,8 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Avalonia.Layout;
+
 namespace Avalonia.Controls
 {
     /// <summary>
@@ -24,8 +26,8 @@ namespace Avalonia.Controls
         /// </summary>
         /// <remarks>
         /// This property should return false until enough children are added to fill the space
-        /// passed into the last measure in the direction of scroll. It should be updated
-        /// immediately after a child is added or removed.
+        /// passed into the last measure or arrange in the direction of scroll. It should be
+        /// updated immediately after a child is added or removed.
         /// </remarks>
         bool IsFull { get; }
 
@@ -63,5 +65,18 @@ namespace Avalonia.Controls
         /// Gets or sets the current pixel offset of the items in the direction of scroll.
         /// </summary>
         double PixelOffset { get; set; }
+
+        /// <summary>
+        /// Invalidates the measure of the control and forces a call to 
+        /// <see cref="IVirtualizingController.UpdateControls"/> on the next measure.
+        /// </summary>
+        /// <remarks>
+        /// The implementation for this method should call
+        /// <see cref="ILayoutable.InvalidateMeasure"/> and also ensure that the next call to
+        /// <see cref="ILayoutable.Measure(Size)"/> calls
+        /// <see cref="IVirtualizingController.UpdateControls"/> on the next measure even if
+        /// the available size hasn't changed.
+        /// </remarks>
+        void ForceInvalidateMeasure();
     }
 }

src/Avalonia.Controls/Platform/ITopLevelImpl.cs

@@ -22,6 +22,11 @@ namespace Avalonia.Platform
         /// </summary>
         Size ClientSize { get; set; }
 
+        /// <summary>
+        /// Gets the maximum size of a window on the system.
+        /// </summary>
+        Size MaxClientSize { get; }
+
         /// <summary>
         /// Gets the scaling factor for the window.
         /// </summary>

src/Avalonia.Controls/Platform/IWindowImpl.cs

@@ -11,11 +11,6 @@ namespace Avalonia.Platform
     /// </summary>
     public interface IWindowImpl : ITopLevelImpl
     {
-        /// <summary>
-        /// Gets the maximum size of a window on the system.
-        /// </summary>
-        Size MaxClientSize { get; }
-
         /// <summary>
         /// Gets or sets the minimized/maximized state of the window.
         /// </summary>

src/Avalonia.Controls/Presenters/ItemVirtualizerSimple.cs

@@ -121,6 +121,7 @@ namespace Avalonia.Controls.Presenters
                             RecycleContainers();
                         }
 
+                        panel.ForceInvalidateMeasure();
                         break;
 
                     case NotifyCollectionChangedAction.Remove:
@@ -130,6 +131,7 @@ namespace Avalonia.Controls.Presenters
                             RecycleContainersOnRemove();
                         }
 
+                        panel.ForceInvalidateMeasure();
                         break;
 
                     case NotifyCollectionChangedAction.Move:
@@ -140,6 +142,7 @@ namespace Avalonia.Controls.Presenters
                     case NotifyCollectionChangedAction.Reset:
                         RecycleContainersOnRemove();
                         CreateAndRemoveContainers();
+                        panel.ForceInvalidateMeasure();
                         break;
                 }
             }

src/Avalonia.Controls/Presenters/ItemsPresenter.cs

@@ -99,7 +99,7 @@ namespace Avalonia.Controls.Presenters
             // the available size.
             if (availableSize == Size.Infinity && VirtualizationMode != ItemVirtualizationMode.None)
             {
-                var window = VisualRoot as Window;
+                var window = VisualRoot as TopLevel;
 
                 if (window != null)
                 {

src/Avalonia.Controls/VirtualizingStackPanel.cs

@@ -19,6 +19,7 @@ namespace Avalonia.Controls
         private double _averageItemSize;
         private int _averageCount;
         private double _pixelOffset;
+        private bool _forceRemeasure;
 
         bool IVirtualizingPanel.IsFull
         {
@@ -61,10 +62,17 @@ namespace Avalonia.Controls
 
         private IVirtualizingController Controller => ((IVirtualizingPanel)this).Controller;
 
+        void IVirtualizingPanel.ForceInvalidateMeasure()
+        {
+            InvalidateMeasure();
+            _forceRemeasure = true;
+        }
+
         protected override Size MeasureOverride(Size availableSize)
         {
-            if (availableSize != ((ILayoutable)this).PreviousMeasure)
+            if (_forceRemeasure || availableSize != ((ILayoutable)this).PreviousMeasure)
             {
+                _forceRemeasure = false;
                 _availableSpace = availableSize;
                 Controller?.UpdateControls();
             }
@@ -74,6 +82,7 @@ namespace Avalonia.Controls
 
         protected override Size ArrangeOverride(Size finalSize)
         {
+            _availableSpace = finalSize;
             _canBeRemoved = 0;
             _takenSpace = 0;
             _averageItemSize = 0;

tests/Avalonia.Controls.UnitTests/Presenters/ItemsPresenterTests_Virtualization_Simple.cs

@@ -658,6 +658,7 @@ namespace Avalonia.Controls.UnitTests.Presenters
             Assert.Equal(expected, actual);
         }
 
+        [Fact]
         public void Should_Add_Containers_For_Items_After_Clear()
         {
             var target = CreateTarget(itemCount: 10);

tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs

@@ -22,7 +22,51 @@ namespace Avalonia.Controls.UnitTests
                 target.Controller = controller.Object;
                 target.Measure(new Size(100, 100));
 
-                controller.Verify(x => x.UpdateControls());
+                controller.Verify(x => x.UpdateControls(), Times.Once());
+            }
+
+            [Fact]
+            public void Measure_Invokes_Controller_UpdateControls_If_AvailableSize_Changes()
+            {
+                var target = (IVirtualizingPanel)new VirtualizingStackPanel();
+                var controller = new Mock<IVirtualizingController>();
+
+                target.Controller = controller.Object;
+                target.Measure(new Size(100, 100));
+                target.InvalidateMeasure();
+                target.Measure(new Size(100, 100));
+                target.InvalidateMeasure();
+                target.Measure(new Size(100, 101));
+
+                controller.Verify(x => x.UpdateControls(), Times.Exactly(2));
+            }
+
+            [Fact]
+            public void Measure_Does_Not_Invoke_Controller_UpdateControls_If_AvailableSize_Is_The_Same()
+            {
+                var target = (IVirtualizingPanel)new VirtualizingStackPanel();
+                var controller = new Mock<IVirtualizingController>();
+
+                target.Controller = controller.Object;
+                target.Measure(new Size(100, 100));
+                target.InvalidateMeasure();
+                target.Measure(new Size(100, 100));
+
+                controller.Verify(x => x.UpdateControls(), Times.Once());
+            }
+
+            [Fact]
+            public void Measure_Invokes_Controller_UpdateControls_If_AvailableSize_Is_The_Same_After_ForceInvalidateMeasure()
+            {
+                var target = (IVirtualizingPanel)new VirtualizingStackPanel();
+                var controller = new Mock<IVirtualizingController>();
+
+                target.Controller = controller.Object;
+                target.Measure(new Size(100, 100));
+                target.ForceInvalidateMeasure();
+                target.Measure(new Size(100, 100));
+
+                controller.Verify(x => x.UpdateControls(), Times.Exactly(2));
             }
 
             [Fact]
@@ -35,7 +79,7 @@ namespace Avalonia.Controls.UnitTests
                 target.Measure(new Size(100, 100));
                 target.Arrange(new Rect(0, 0, 110, 110));
 
-                controller.Verify(x => x.UpdateControls());
+                controller.Verify(x => x.UpdateControls(), Times.Exactly(2));
             }
 
             [Fact]
@@ -118,6 +162,20 @@ namespace Avalonia.Controls.UnitTests
                 Assert.Equal(2, target.PixelOverflow);
             }
 
+            [Fact]
+            public void Reports_PixelOverflow_After_Arrange_Smaller_Than_Measure()
+            {
+                var target = (IVirtualizingPanel)new VirtualizingStackPanel();
+
+                target.Children.Add(new Canvas { Width = 50, Height = 50 });
+                target.Children.Add(new Canvas { Width = 50, Height = 52 });
+
+                target.Measure(new Size(100, 100));
+                target.Arrange(new Rect(0, 0, 50, 50));
+
+                Assert.Equal(52, target.PixelOverflow);
+            }
+
             [Fact]
             public void Reports_PixelOverflow_With_PixelOffset()
             {