A quick and dirty Google Reader client implementation built in C# with Xamarin using the new async support.

GReader.cs

using System;
using System.Net;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Text.RegularExpressions;

using SQLite;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace GReaderTest
{
    public class Feed
    {
		[PrimaryKey]
		public string Id { get; set; }
		public string SortId { get; set; }
		public string Title { get; set; }
	}

	public class Tag
	{
		[PrimaryKey]
		public string Id { get; set; }
		public string SortId { get; set; }
		public string Title { get; set; }
	}

	public class Entry
	{
		[PrimaryKey]
		public string Id { get; set; }
		public string Title { get; set; }
		public int Date { get; set; }
		public string Author { get; set; }
		public string Content { get; set; }
		public string Feed { get; set; }
	}

	public class GReader
	{
		const string ApiBase = "http://www.google.com/reader/api";

		SQLiteConnection Storage { get; set; }

		string AuthToken { get; set; }

		public GReader ()
		{
			Storage = new SQLiteConnection ("test.db");
			Storage.CreateTable<Feed> ();
			Storage.CreateTable<Tag> ();
			Storage.CreateTable<Entry> ();
		}

		~GReader()
		{
			Storage.Close ();
		}

		public async Task LoadFeedData()
		{
			var client = new WebClient ();
			client.Headers.Set ("Authorization", String.Format ("GoogleLogin auth={0}", AuthToken));

			var subs = await client.DownloadStringTaskAsync (ApiBase + "/0/subscription/list?output=json");
			var tags = await client.DownloadStringTaskAsync (ApiBase + "/0/tag/list?output=json");

			var subdata = from item in JObject.Parse (subs) ["subscriptions"] select new Feed () {
				Id = (string)item["id"],
				SortId = (string)item["sortid"],
				Title = (string)item["title"],
			};

			var tagdata = from item in JObject.Parse (tags) ["tags"] select new Tag () {
				Id = (string)item["id"],
				SortId = (string)item["sortid"],
				Title = ((string)item["id"]).Split('/').Last(),
			};

			Storage.BeginTransaction ();
			foreach (var item in subdata) Storage.InsertOrReplace (item);
			foreach (var item in tagdata) Storage.InsertOrReplace (item);
			Storage.Commit ();
		}

		public Entry ParseEntry (JToken entry)
		{
			try {
				var content = entry ["content"] != null ? entry ["content"] ["content"] :
					      entry ["summary"] != null ? entry ["summary"] ["content"] : "";

				return new Entry () {
					Id = (string)entry["id"],
					Title = (string)entry["title"],
					Author = (string)entry["author"],
					Date = (int)entry["published"],
					Feed = (string)entry["origin"]["streamId"],
					Content = (string)content,
				};
			}
			catch (Exception e) {
				Console.WriteLine("Failed to parse entry: {0}", entry.ToString());
				return new Entry();
			}
		}

		public async Task<List<Entry>> DownloadEntries (string id)
		{
			try {
				var data = await new WebClient().DownloadStringTaskAsync(ApiBase + "/0/stream/contents/" + id);
				return JObject.Parse(data) ["items"].Select(ParseEntry).ToList();
			}
			catch (Exception e) {
				Console.WriteLine("Failed to parse feed: {0} - {1}", id, e.Message);
				return new List<Entry>();
			}
		}

		public async Task LoadEntries()
		{
			var urls = Storage.Table<Feed> ().ToList().Select(row => row.Id).ToList();
			var output = await Task.WhenAll (urls.Select (u => DownloadEntries (u)));

			Storage.BeginTransaction ();
			foreach (var feed in output)
				foreach (var entry in feed)
					Storage.InsertOrReplace (entry);
			Storage.Commit ();

			Console.WriteLine ("Finished!");
		}

		public async Task<string> Authenticate(string username, string passwd)
		{
			var address = String.Format ("{0}?service=reader&Email={1}&Passwd={2}", ApiBase, username, passwd);
			var regex = new Regex ("SID=(?<SID>.+)\nLSID=(.*)\nAuth=(?<Auth>.*)");
			var response = new WebClient().DownloadStringTaskAsync (new Uri (address));
			return regex.Matches (await response)[0].Groups["Auth"].Value;
		}
	}
}