Ensure IsSelected set on ApplyTemplate.

Perspex.Controls/Primitives/SelectingItemsControl.cs

@@ -191,6 +191,12 @@ namespace Perspex.Controls.Primitives
             e.Handled = true;
         }
 
+        protected override void OnTemplateApplied()
+        {
+            base.OnTemplateApplied();
+            this.SelectedItemChanged(this.SelectedItem);
+        }
+
         private static int CoerceSelectedIndex(PerspexObject o, int value)
         {
             var control = o as SelectingItemsControl;

Tests/Perspex.Controls.UnitTests/Primitives/SelectingItemsControlTests.cs

@@ -57,6 +57,28 @@ namespace Perspex.Controls.Primitives.UnitTests
             Assert.True(items[1].IsSelected);
         }
 
+        [Fact]
+        public void Setting_SelectedItem_Before_ApplyTemplate_Should_Set_Item_IsSelected_True()
+        {
+            var items = new[]
+            {
+                new Item(),
+                new Item(),
+            };
+
+            var target = new Target
+            {
+                Items = items,
+                Template = this.Template(),
+            };
+
+            target.SelectedItem = items[1];
+            target.ApplyTemplate();
+
+            Assert.False(items[0].IsSelected);
+            Assert.True(items[1].IsSelected);
+        }
+
         [Fact]
         public void Setting_SelectedItem_Should_Set_SelectedIndex()
         {