NSUrlConnectionクラスを使って文字列を非同期ダウンロードするコードを書いたら結構大変なことになった。

gistfile1.cs

using System;
using System.Drawing;

using MonoTouch.Foundation;
using MonoTouch.UIKit;
using System.Net;
using System.IO;

namespace WebRequestSample
{
  // これがViewControllerのクラス
	public partial class WebRequestSampleViewController : UIViewController
	{
		// 〜省略	
		
		public void DidDownloaded (object sender, EventArgs e)
		{
			var customDelegate = sender as CustomDelegate;
			label.Text = customDelegate.GetResultText();
		}

		void DownloadUsingNSUrlRequest (object sender, EventArgs e)
		{
			var downloadedDelegate = new CustomDelegate(this);

			var req = new NSUrlRequest(new NSUrl("http://ch3cooh.hatenablog.jp/"));
			NSUrlConnection connection = new NSUrlConnection(req, downloadedDelegate);
			connection.Start();
		} 
		
		// 〜省略	
	}	
	
	// NSUrlConnectionを使ったダウンロード中に発生するイベントを受け止めるCustomDelegateクラス
	public class CustomDelegate : NSUrlConnectionDelegate
	{
		public byte[] ResponseData { get; set; }
		private long _receivedDataLength { get; set; }
		private WebRequestSampleViewController _delegate;

		public CustomDelegate(WebRequestSampleViewController viewController)
		{
			_delegate = viewController;
		}

		public override void ReceivedResponse (NSUrlConnection connection, NSUrlResponse response)
		{
			long length = response.ExpectedContentLength;
			if (length == -1) {
				length = 1* 1024 * 1024;
			}
			ResponseData = new byte[length];
			_receivedDataLength = 0;
		}

		public override void ReceivedData (NSUrlConnection connection, NSData data)
		{
			System.Runtime.InteropServices.Marshal.Copy(
				data.Bytes, ResponseData, (int)_receivedDataLength, (int)data.Length);
			_receivedDataLength += data.Length;
		}

		public override void FinishedLoading (NSUrlConnection connection)
		{
			_delegate.DidDownloaded(this, new EventArgs());
		}

		public string GetResultText()
		{
			return System.Text.UTF8Encoding.UTF8.GetString(
				ResponseData, 0,  (int)_receivedDataLength);
		}
	}
}