Added RefreshObject and IsExpanded

RefreshObject notifies tree of changes to a model (e.g. it's children) and clears cached knowledge but persists the branch expansion state

UnitTests/TreeViewTests.cs

@@ -40,7 +40,51 @@ namespace UnitTests {
 			return tree;
 		}
 		#endregion
+		
+		/// <summary>
+		/// Tests that <see cref="TreeView.Expand(object)"/> and <see cref="TreeView.IsExpanded(object)"/> are consistent
+		/// </summary>
+		[Fact]
+		public void IsExpanded_TrueAfterExpand()
+		{
+			var tree = CreateTree(out Factory f, out _, out _);
+			Assert.False(tree.IsExpanded(f));
 
+			tree.Expand(f);
+			Assert.True(tree.IsExpanded(f));
+
+			tree.Collapse(f);
+			Assert.False(tree.IsExpanded(f));
+		}
+
+		/// <summary>
+		/// Tests that <see cref="TreeView.IsExpanded(object)"/> and <see cref="TreeView.Expand(object)"/> behaves correctly when an object cannot be expanded (because it has no children)
+		/// </summary>
+		[Fact]
+		public void IsExpanded_FalseIfCannotExpand()
+		{
+			var tree = CreateTree(out Factory f, out Car c, out _);
+			
+			// expose the car by expanding the factory
+			tree.Expand(f);
+
+			// car is not expanded
+			Assert.False(tree.IsExpanded(c));
+
+			//try to expand the car (should have no effect because cars have no children)
+			tree.Expand(c);
+			
+			Assert.False(tree.IsExpanded(c));
+
+			// should also be ignored
+			tree.Collapse(c);
+
+			Assert.False(tree.IsExpanded(c));
+		}
+
+		/// <summary>
+		/// Tests illegal ranges for <see cref="TreeView.ScrollOffset"/>
+		/// </summary>
 		[Fact]
 		public void ScrollOffset_CannotBeNegative()
 		{
@@ -56,27 +100,72 @@ namespace UnitTests {
 		}
 
 
+		/// <summary>
+		/// Tests <see cref="TreeView.GetScrollOffsetOf(object)"/> for objects that are as yet undiscovered by the tree
+		/// </summary>
 		[Fact]
 		public void GetScrollOffsetOf_MinusOneForUnRevealed()
 		{
 			var tree = CreateTree(out Factory f, out Car c1, out Car c2);
 			
+			// to start with the tree is collapsed and only knows about the root object
 			Assert.Equal(0,tree.GetScrollOffsetOf(f));
 			Assert.Equal(-1,tree.GetScrollOffsetOf(c1));
 			Assert.Equal(-1,tree.GetScrollOffsetOf(c2));
 
+			// reveal it by expanding the root object
+			tree.Expand(f);
+			
+			// tree now knows about children
+			Assert.Equal(0,tree.GetScrollOffsetOf(f));
+			Assert.Equal(1,tree.GetScrollOffsetOf(c1));
+			Assert.Equal(2,tree.GetScrollOffsetOf(c2));
+
+			// after collapsing the root node again
+			tree.Collapse(f);
+			
+			// tree no longer knows about the locations of these objects
+			Assert.Equal(0,tree.GetScrollOffsetOf(f));
+			Assert.Equal(-1,tree.GetScrollOffsetOf(c1));
+			Assert.Equal(-1,tree.GetScrollOffsetOf(c2));
+		}
+
+		/// <summary>
+		/// Simulates behind the scenes changes to an object (which children it has) and how to sync that into the tree using <see cref="TreeView.RefreshObject(object, bool)"/>
+		/// </summary>
+		[Fact]
+		public void RefreshObject_ChildRemoved()
+		{
+			var tree = CreateTree(out Factory f, out Car c1, out Car c2);
+			
 			//reveal it by expanding the root object
 			tree.Expand(f);
 			
 			Assert.Equal(0,tree.GetScrollOffsetOf(f));
 			Assert.Equal(1,tree.GetScrollOffsetOf(c1));
 			Assert.Equal(2,tree.GetScrollOffsetOf(c2));
-
-			tree.Collapse(f);
 			
+			// Factory now no longer makes Car c1 (only c2)
+			f.Cars = new Car[]{c2};
+
+			// Tree does not know this yet
+			Assert.Equal(0,tree.GetScrollOffsetOf(f));
+			Assert.Equal(1,tree.GetScrollOffsetOf(c1));
+			Assert.Equal(2,tree.GetScrollOffsetOf(c2));
+
+			// If the user has selected the node c1
+			tree.SelectedObject = c1;
+
+			// When we refresh the tree
+			tree.RefreshObject(f);
+
+			// Now tree knows that factory has only one child node c2
 			Assert.Equal(0,tree.GetScrollOffsetOf(f));
 			Assert.Equal(-1,tree.GetScrollOffsetOf(c1));
-			Assert.Equal(-1,tree.GetScrollOffsetOf(c2));
+			Assert.Equal(1,tree.GetScrollOffsetOf(c2));
+
+			// The old selection was c1 which is now gone so selection should default to the parent of that branch (the factory)
+			Assert.Equal(f,tree.SelectedObject);
 		}
 	}
 }