Begin on setting properties on child components

src/Microsoft.AspNetCore.Blazor/RenderTree/RenderTreeDiffComputer.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using Microsoft.AspNetCore.Blazor.Components;
 using Microsoft.AspNetCore.Blazor.Rendering;
 
 namespace Microsoft.AspNetCore.Blazor.RenderTree
@@ -339,7 +338,7 @@ namespace Microsoft.AspNetCore.Blazor.RenderTree
                         throw new InvalidOperationException($"Child component already exists during {nameof(InstantiateChildComponents)}");
                     }
 
-                    _renderer.InstantiateChildComponent(ref nodes[i]);
+                    _renderer.InstantiateChildComponent(nodes, i);
                 }
             }
         }

src/Microsoft.AspNetCore.Blazor/Rendering/Renderer.cs

@@ -42,23 +42,6 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
             }
         }
 
-        internal void InstantiateChildComponent(ref RenderTreeNode node)
-        {
-            if (node.NodeType != RenderTreeNodeType.Component)
-            {
-                throw new ArgumentException($"The node's {nameof(RenderTreeNode.NodeType)} property must equal {RenderTreeNodeType.Component}", nameof(node));
-            }
-
-            if (node.Component != null)
-            {
-                throw new ArgumentException($"The node already has a non-null component instance", nameof(node));
-            }
-
-            var newComponent = (IComponent)Activator.CreateInstance(node.ComponentType);
-            var newComponentId = AssignComponentId(newComponent);
-            node.SetChildComponentInstance(newComponentId, newComponent);
-        }
-
         /// <summary>
         /// Updates the visible UI to display the supplied <paramref name="renderTree"/>
         /// at the location corresponding to the <paramref name="componentId"/>.
@@ -84,9 +67,46 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
         protected void DispatchEvent(int componentId, int renderTreeIndex, UIEventArgs eventArgs)
             => GetRequiredComponentState(componentId).DispatchEvent(renderTreeIndex, eventArgs);
 
+        internal void InstantiateChildComponent(RenderTreeNode[] nodes, int componentNodeIndex)
+        {
+            ref var node = ref nodes[componentNodeIndex];
+            if (node.NodeType != RenderTreeNodeType.Component)
+            {
+                throw new ArgumentException($"The node's {nameof(RenderTreeNode.NodeType)} property must equal {RenderTreeNodeType.Component}", nameof(node));
+            }
+
+            if (node.Component != null)
+            {
+                throw new ArgumentException($"The node already has a non-null component instance", nameof(node));
+            }
+
+            var newComponent = (IComponent)Activator.CreateInstance(node.ComponentType);
+            var newComponentId = AssignComponentId(newComponent);
+            node.SetChildComponentInstance(newComponentId, newComponent);
+            SetPropertiesOnComponent(nodes, componentNodeIndex);
+        }
+
         private ComponentState GetRequiredComponentState(int componentId)
             => _componentStateById.TryGetValue(componentId, out var componentState)
                 ? componentState
                 : throw new ArgumentException($"The renderer does not have a component with ID {componentId}.");
+
+        private void SetPropertiesOnComponent(RenderTreeNode[] nodes, int componentNodeIndex)
+        {
+            ref var componentNode = ref nodes[componentNodeIndex];
+            var component = componentNode.Component;
+            var descendantsEndIndex = componentNode.ElementDescendantsEndIndex;
+            for (var attributeNodeIndex = componentNodeIndex + 1; attributeNodeIndex <= descendantsEndIndex; attributeNodeIndex++)
+            {
+                SetPropertyOnComponent(component, nodes[attributeNodeIndex]);
+            }
+        }
+
+        private void SetPropertyOnComponent(IComponent component, in RenderTreeNode attributeNode)
+        {
+            // TODO: Cache the reflection
+            var property = component.GetType().GetProperty(attributeNode.AttributeName);
+            property.SetValue(component, attributeNode.AttributeValue);
+        }
     }
 }

test/Microsoft.AspNetCore.Blazor.Test/RenderTreeDiffComputerTest.cs

@@ -674,6 +674,39 @@ namespace Microsoft.AspNetCore.Blazor.Test
                 entry => AssertEdit(entry, RenderTreeEditType.StepOut, 0));
         }
 
+        [Fact]
+        public void SetsKnownPropertiesOnChildComponents()
+        {
+            // Arrange
+            var renderer = new FakeRenderer();
+            var oldTree = new RenderTreeBuilder(renderer);
+            var newTree = new RenderTreeBuilder(renderer);
+            var diff = new RenderTreeDiffComputer(renderer);
+            var testObject = new object();
+            newTree.OpenComponentElement<FakeComponent>(0);
+            //newTree.AddAttribute(1, nameof(FakeComponent.IntProperty), 123);
+            newTree.AddAttribute(2, nameof(FakeComponent.StringProperty), "some string");
+            //newTree.AddAttribute(3, nameof(FakeComponent.ObjectProperty), testObject);
+            newTree.CloseElement();
+
+            // Act
+            var result = diff.ApplyNewRenderTreeVersion(oldTree.GetNodes(), newTree.GetNodes());
+            var componentInstance = newTree.GetNodes().First().Component as FakeComponent;
+
+            // Assert
+            AssertEdit(result.Edits.Single(), RenderTreeEditType.PrependNode, 0);
+            Assert.NotNull(componentInstance);
+            //Assert.Equal(123, componentInstance.IntProperty);
+            Assert.Equal("some string", componentInstance.StringProperty);
+            //Assert.Same(testObject, componentInstance.ObjectProperty);
+        }
+
+        [Fact]
+        public void RejectsUnknownPropertiesOnChildComponents()
+        {
+
+        }
+
         [Fact]
         public void RetainsChildComponentsForExistingNodes()
         {
@@ -722,6 +755,12 @@ namespace Microsoft.AspNetCore.Blazor.Test
 
         private class FakeComponent : IComponent
         {
+            public int IntProperty { get; set; }
+            public string StringProperty { get; set; }
+            public object ObjectProperty { get; set; }
+            public string ReadonlyProperty { get; private set; }
+            private string PrivateProperty { get; set; }
+
             public void BuildRenderTree(RenderTreeBuilder builder)
                 => throw new NotImplementedException();
         }