More tests, futureproofing + 2 bugfixes

src/Avalonia.Controls/Grid.cs

@@ -105,6 +105,7 @@ namespace Avalonia.Controls
 
                 _columnDefinitions = value;
                 _columnDefinitions.TrackItemPropertyChanged(_ => InvalidateMeasure());
+                _columnDefinitions.CollectionChanged += (_, __) => InvalidateMeasure();
             }
         }
 
@@ -132,6 +133,7 @@ namespace Avalonia.Controls
 
                 _rowDefinitions = value;
                 _rowDefinitions.TrackItemPropertyChanged(_ => InvalidateMeasure());
+                _rowDefinitions.CollectionChanged += (_, __) => InvalidateMeasure();
             }
         }
 

src/Avalonia.Controls/Utils/SharedSizeScopeHost.cs

@@ -52,6 +52,7 @@ namespace Avalonia.Controls
                 grid.RowDefinitions.CollectionChanged += DefinitionsCollectionChanged;
                 grid.ColumnDefinitions.CollectionChanged += DefinitionsCollectionChanged;
 
+
                 _subscriptions = new CompositeDisposable(
                     Disposable.Create(() => grid.RowDefinitions.CollectionChanged -= DefinitionsCollectionChanged),
                     Disposable.Create(() => grid.ColumnDefinitions.CollectionChanged -= DefinitionsCollectionChanged),
@@ -60,6 +61,13 @@ namespace Avalonia.Controls
 
             }
 
+            // method to be hooked up once RowDefinitions/ColumnDefinitions collections can be replaced on a grid
+            private void DefinitionsChanged(object sender, AvaloniaPropertyChangedEventArgs e)
+            {
+                // route to collection changed as a Reset.
+                DefinitionsCollectionChanged(null, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
+            }
+
             private void DefinitionPropertyChanged(Tuple<object, PropertyChangedEventArgs> propertyChanged)
             {
                 if (propertyChanged.Item2.PropertyName == nameof(DefinitionBase.SharedSizeGroup))
@@ -78,7 +86,9 @@ namespace Avalonia.Controls
                     offset = Grid.RowDefinitions.Count;
 
                 var newItems = e.NewItems?.OfType<DefinitionBase>().Select(db => new MeasurementResult(Grid, db)).ToList() ?? new List<MeasurementResult>();
-                var oldItems = Results.GetRange(e.OldStartingIndex + offset, e.OldItems?.Count ?? 0);
+                var oldItems = e.OldStartingIndex >= 0 
+                                    ? Results.GetRange(e.OldStartingIndex + offset, e.OldItems.Count) 
+                                    : new List<MeasurementResult>();
 
                 void NotifyNewItems()
                 {

tests/Avalonia.Controls.UnitTests/SharedSizeScopeTests.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
@@ -149,6 +150,90 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(0, grids[0].ColumnDefinitions[0].ActualWidth);
         }
 
+        [Fact]
+        public void Collection_Changes_Are_Tracked()
+        {
+            var grid = CreateGrid(
+                ("A", new GridLength(20)),
+                ("A", new GridLength(30)),
+                ("A", new GridLength(40)),
+                (null, new GridLength()));
+
+            var scope = new Panel();
+            scope.Children.Add(grid);
+
+            var root = new TestRoot();
+            root.SetValue(Grid.IsSharedSizeScopeProperty, true);
+            root.Child = scope;
+
+            grid.Measure(new Size(200, 200));
+            grid.Arrange(new Rect(new Point(), new Point(200, 200)));
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(40, cd.ActualWidth));
+
+            grid.ColumnDefinitions.RemoveAt(2);
+
+            grid.Measure(new Size(200, 200));
+            grid.Arrange(new Rect(new Point(), new Point(200, 200)));
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(30, cd.ActualWidth));
+
+            grid.ColumnDefinitions.Insert(1, new ColumnDefinition { Width = new GridLength(35), SharedSizeGroup = "A" });
+
+            grid.Measure(new Size(200, 200));
+            grid.Arrange(new Rect(new Point(), new Point(200, 200)));
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(35, cd.ActualWidth));
+
+            grid.ColumnDefinitions[1] = new ColumnDefinition { Width = new GridLength(10), SharedSizeGroup = "A" };
+
+            grid.Measure(new Size(200, 200));
+            grid.Arrange(new Rect(new Point(), new Point(200, 200)));
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(30, cd.ActualWidth));
+
+            grid.ColumnDefinitions[1] = new ColumnDefinition { Width = new GridLength(50), SharedSizeGroup = "A" };
+
+            grid.Measure(new Size(200, 200));
+            grid.Arrange(new Rect(new Point(), new Point(200, 200)));
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(50, cd.ActualWidth));
+        }
+
+        [Fact]
+        public void Size_Priorities_Are_Maintained()
+        {
+            var sizers = new List<Control>();
+            var grid = CreateGrid(
+                ("A", new GridLength(20)), 
+                ("A", new GridLength(20, GridUnitType.Auto)), 
+                ("A", new GridLength(1, GridUnitType.Star)), 
+                ("A", new GridLength(1, GridUnitType.Star)),
+                (null, new GridLength()));
+            for (int i = 0; i < 3; i++)
+                sizers.Add(AddSizer(grid, i, 6 + i * 6));
+            var scope = new Panel();
+            scope.Children.Add(grid);
+
+            var root = new TestRoot();
+            root.SetValue(Grid.IsSharedSizeScopeProperty, true);
+            root.Child = scope;
+
+            grid.Measure(new Size(100, 100));
+            grid.Arrange(new Rect(new Point(), new Point(100, 100)));
+            // all in group are equal to the first fixed column
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(20, cd.ActualWidth));
+
+            grid.ColumnDefinitions[0].SharedSizeGroup = null;
+
+            grid.Measure(new Size(100, 100));
+            grid.Arrange(new Rect(new Point(), new Point(100, 100)));
+            // all in group are equal to width (MinWidth) of the sizer in the second column
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(6 + 1 * 6, cd.ActualWidth));
+
+            grid.ColumnDefinitions[1].SharedSizeGroup = null;
+
+            grid.Measure(new Size(double.PositiveInfinity, 100));
+            grid.Arrange(new Rect(new Point(), new Point(100, 100)));
+            // with no constraint star columns default to the MinWidth of the sizer in the column
+            Assert.All(grid.ColumnDefinitions.Where(cd => cd.SharedSizeGroup == "A"), cd => Assert.Equal(6 + 2 * 6, cd.ActualWidth));
+        }
+
         // grid creators
         private Grid CreateGrid(params string[] columnGroups)
         {
@@ -187,5 +272,13 @@ namespace Avalonia.Controls.UnitTests
 
             return grid;
         }
+
+        private Control AddSizer(Grid grid, int column, double size = 30)
+        {
+            var ctrl = new Control {  MinWidth = size, MinHeight = size };
+            ctrl.SetValue(Grid.ColumnProperty,column);
+            grid.Children.Add(ctrl);
+            return ctrl;
+        }
     }
 }