Add SortDescription for object comparer

#881

Author: twsouthwick

Microsoft.Toolkit.Uwp.UI/AdvancedCollectionView/AdvancedCollectionView.cs

@@ -368,15 +368,29 @@ int IComparer<object>.Compare(object x, object y)
                 var typeInfo = x.GetType().GetTypeInfo();
                 foreach (var sd in _sortDescriptions)
                 {
-                    _sortProperties[sd.PropertyName] = typeInfo.GetDeclaredProperty(sd.PropertyName);
+                    if (!string.IsNullOrEmpty(sd.PropertyName))
+                    {
+                        _sortProperties[sd.PropertyName] = typeInfo.GetDeclaredProperty(sd.PropertyName);
+                    }
                 }
             }
 
             foreach (var sd in _sortDescriptions)
             {
-                var pi = _sortProperties[sd.PropertyName];
-                var cx = pi.GetValue(x) as IComparable;
-                var cy = pi.GetValue(y) as IComparable;
+                IComparable cx, cy;
+
+                if (string.IsNullOrEmpty(sd.PropertyName))
+                {
+                    cx = x as IComparable;
+                    cy = y as IComparable;
+                }
+                else
+                {
+                    var pi = _sortProperties[sd.PropertyName];
+                    cx = pi.GetValue(x) as IComparable;
+                    cy = pi.GetValue(y) as IComparable;
+                }
+
                 try
                 {
                     // ReSharper disable once PossibleUnintendedReferenceComparison

Microsoft.Toolkit.Uwp.UI/AdvancedCollectionView/SortDescription.cs

@@ -20,12 +20,22 @@ public class SortDescription
         /// <summary>
         /// Gets the name of property to sort on
         /// </summary>
-        public string PropertyName { get; private set; }
+        public string PropertyName { get; }
 
         /// <summary>
         /// Gets the direction of sort
         /// </summary>
-        public SortDirection Direction { get; private set; }
+        public SortDirection Direction { get; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SortDescription"/> class that describes
+        /// a sort on the object itself
+        /// </summary>
+        /// <param name="direction">direction of sort</param>
+        public SortDescription(SortDirection direction)
+        {
+            Direction = direction;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="SortDescription"/> class.

UnitTests/UI/Person.cs

@@ -10,15 +10,29 @@
 // THE CODE OR THE USE OR OTHER DEALINGS IN THE CODE.
 // ******************************************************************
 
+using System;
+
 namespace UnitTests.UI
 {
     /// <summary>
     /// Sample class to test AdvancedCollectionViewSource functionality
     /// </summary>
-    internal class Person
+    internal class Person : IComparable
     {
         public string Name { get; set; }
 
         public int Age { get; set; }
+
+        public int CompareTo(object obj)
+        {
+            var other = obj as Person;
+
+            if (other == null)
+            {
+                return -1;
+            }
+
+            return Age.CompareTo(other.Age);
+        }
     }
 }

UnitTests/UI/Test_AdvancedCollectionView.cs

@@ -180,5 +180,54 @@ public void Test_AdvancedCollectionView_Combined()
             Assert.AreEqual(((Person)a.First()).Age, 42);
             Assert.AreEqual(a.Count, 2);
         }
+
+        [TestCategory("AdvancedCollectionView")]
+        [UITestMethod]
+        public void Test_AdvancedCollectionView_Sorting_OnSelf()
+        {
+            var l = new ObservableCollection<Person>
+            {
+                new Person()
+                {
+                    Name = "lorem",
+                    Age = 4
+                },
+                new Person()
+                {
+                    Name = "imsum",
+                    Age = 8
+                },
+                new Person()
+                {
+                    Name = "dolor",
+                    Age = 15
+                },
+                new Person()
+                {
+                    Name = "sit",
+                    Age = 16
+                },
+                new Person()
+                {
+                    Name = "amet",
+                    Age = 23
+                },
+                new Person()
+                {
+                    Name = "consectetur",
+                    Age = 42
+                },
+            };
+
+            var a = new AdvancedCollectionView(l)
+            {
+                SortDescriptions =
+                {
+                    new SortDescription(SortDirection.Descending)
+                }
+            };
+
+            Assert.AreEqual(((Person)a.First()).Age, 42);
+        }
     }
 }