Merge pull request #2655 from cwensley/curtis/fix-binding-context-wit…

…h-parent-change

Trigger DataContextChanged when parent change causes DataContext to be null

src/Eto/Forms/Binding/BindableWidget.cs

@@ -93,9 +93,10 @@ public Widget Parent
 		get => Properties.Get<Widget>(Parent_Key);
 		internal protected set
 		{
+			var dataContext = DataContext;
 			if (Properties.TrySet(Parent_Key, value))
 			{
-				if (!HasDataContext && !(DataContext is null))
+				if (!HasDataContext && !ReferenceEquals(DataContext, dataContext))
 				{
 					IsDataContextChanging = true;
 					OnDataContextChanged(EventArgs.Empty);

test/Eto.Test/UnitTests/Forms/DataContextTests.cs

@@ -436,6 +436,30 @@ public void ChangingDataContextShouldNotSetValues() => Shown(
 				Assert.AreEqual(0, model1.SelectedIndex, "#3 - Model 1 was changed");
 				Assert.AreEqual(1, model2.SelectedIndex, "#4 - Model 2 was changed");
 			});
+
+		[Test]
+		public void RemovingFromParentShouldTriggerBindingChanged() => Invoke(() =>
+		{
+			int parentDataContextChanged = 0;
+			int childDataContextChanged = 0;
+			var panel = new Panel();
+			panel.DataContextChanged += (sender, e) => parentDataContextChanged++;
+
+			panel.DataContext = new MyViewModelWithEquals { ID = 10 };
+			Assert.AreEqual(1, parentDataContextChanged);
+
+			var child = new Panel();
+			child.DataContextChanged += (sender, e) => childDataContextChanged++;
+
+			panel.Content = child;
+			Assert.AreEqual(1, childDataContextChanged);
+			Assert.AreSame(child.DataContext, panel.DataContext);
+
+			panel.Content = null;
+			Assert.AreEqual(2, childDataContextChanged);
+			Assert.AreEqual(1, parentDataContextChanged);
+			Assert.IsNull(child.DataContext);
+		});
 	}
 }