mcs/class/System.ComponentModel.Composition/src/ComponentModel/System/ComponentModel/Composition/MetadataServices.cs

   1 // -----------------------------------------------------------------------\r
   2 // Copyright (c) Microsoft Corporation.  All rights reserved.\r
   3 // -----------------------------------------------------------------------\r
   4 using System;\r
   5 using System.Collections.Generic;\r
   6 using Microsoft.Internal;\r
   7 using Microsoft.Internal.Collections;\r
   8 \r
   9 namespace System.ComponentModel.Composition\r
  10 {\r
  11     internal static class MetadataServices\r
  12     {\r
  13         public static readonly IDictionary<string, object> EmptyMetadata = new ReadOnlyDictionary<string, object>(null);\r
  14 \r
  15         public static IDictionary<string, object> AsReadOnly(this IDictionary<string, object> metadata)\r
  16         {\r
  17             if (metadata == null)\r
  18             {\r
  19                 return EmptyMetadata;\r
  20             }\r
  21 \r
  22             if (metadata is ReadOnlyDictionary<string, object>)\r
  23             {\r
  24                 return metadata;\r
  25             }\r
  26 \r
  27             return new ReadOnlyDictionary<string, object>(metadata);\r
  28         }\r
  29 \r
  30         public static T GetValue<T>(this IDictionary<string, object> metadata, string key)\r
  31         {\r
  32             Assumes.NotNull(metadata, "metadata");\r
  33 \r
  34             object untypedValue = true;\r
  35             if (!metadata.TryGetValue(key, out untypedValue))\r
  36             {\r
  37                 return default(T);\r
  38             }\r
  39 \r
  40             if (untypedValue is T)\r
  41             {\r
  42                 return (T)untypedValue;\r
  43             }\r
  44             else\r
  45             {\r
  46                 return default(T);\r
  47             }\r
  48         }\r
  49     }\r
  50 }\r