/**
         * 1.加载指定路径的文件
         * 2.读取文件的内容
         * 3.把 json 转化为对象(用到了第三方库  Newtonsoft.Json )
         **/
        public async Task<IList<RecipeGroup>> GetRecipeGroups()
        {
            // Read RecipeData.json from this PCL's DataModel folder
            var name = typeof(RecipeService).AssemblyQualifiedName.Split(',')[1].Trim();
            var assembly = Assembly.Load(new AssemblyName(name));
            var stream = assembly.GetManifestResourceStream(name + ".Data.RecipeData.json");

            // Parse the JSON and generate a collection of RecipeGroup objects
            using (var reader = new StreamReader(stream))
            {
                string json = await reader.ReadToEndAsync();
                var obj = new { Groups = new List<RecipeGroup>() };
                var result = JsonConvert.DeserializeAnonymousType(json, obj);
                return result.Groups;
            }
        }