completed the branch

src/Shared/HandyControl_Shared/Tools/Extension/EnumerableExtension.cs

@@ -16,5 +16,16 @@ namespace HandyControl.Tools.Extension
 
             return enumerable;
         }
+
+        public static IEnumerable<TSource> DoWithIndex<TSource>(this IEnumerable<TSource> source, Action<TSource, int> predicate)
+        {
+            var enumerable = source as IList<TSource> ?? source.ToList();
+            for (var i = 0; i < enumerable.Count; i++)
+            {
+                predicate.Invoke(enumerable[i], i);
+            }
+
+            return enumerable;
+        }
     }
 }