add some helpers

Author: hez2010

Files/Helpers/StorageItemHelpers.cs

@@ -12,6 +12,11 @@ class StorageItemHelpers
     {
         public static async Task<IStorageItem> PathToStorageItemAsync(string path, Type type)
         {
+            if (type == typeof(IStorageItem))
+            {
+                throw new InvalidOperationException("An implementation type is needed.");
+            }
+
             if (type == typeof(StorageFile))
             {
                 return await StorageFile.GetFileFromPathAsync(path).AsTask();
@@ -35,9 +40,9 @@ public static async Task<IStorageItem> PathToStorageItemAsync(string path, Type
             throw new InvalidOperationException();
         }
 
-        public static Task<IStorageItem> PathToStorageItemAsync<T>(string path) where T : IStorageItem
+        public static async Task<T> PathToStorageItemAsync<T>(string path) where T : IStorageItem
         {
-            return PathToStorageItemAsync(path, typeof(T));
+            return (T)await PathToStorageItemAsync(path, typeof(T));
         }
 
         public static bool Exists(string path)