An excerpt from my MonoTouch book (it’s from the rough cuts version) is available as an article at InformIT: Learning MonoTouch: A Hands-On Guide to Building iOS Applications with C# and .NET – Common iOS Classes.

Someone was asking about Bonjour examples in MonoTouch in irc yesterday so I threw this quick and dirty sample together. If you’re not familiar, Bonjour is Apple’s zeroconf networking implementation. It is open-source and even includes a version for Windows. Bonjour allows you to publish and discover services without needing pre-configured information. It’s all about the discovery of services. The actual implementation of the server and client networking code is up to you (I haven’t included that in this example however).

To use Bonjour with MonoTouch, you deal primarily with two classes, NSNetService and NSNetServiceBrowser. NSNetService is used to publish and resolve services. NSNetServiceBrowser, as the name suggests, allows you to browse for services. Once you have discovered a service via a browse, you resolve it in a separate operation, after which you can implement whatever networking code you like to communicate with the service.

In this simple example I publish a service when the application finishes launching and browse from a view controller that includes a table and a text view. The table displays each service as it is discovered. Selecting the row in the table associated with a particular service calls resolve on the service. Adding, removing and resolution of services is logged in the text view.

Here’s the relevant code that does the service publication:

        NetDelegate _netDel;
        NSNetService _ns;

        void InitNetService ()
        {
            _ns = new NSNetService ("", "_testservice._tcp", UIDevice.CurrentDevice.Name, 9999);
            _netDel = new NetDelegate ();
            _ns.Delegate = _netDel;
            _ns.Publish ();
        }

        class NetDelegate : NSNetServiceDelegate
        {
            public override void Published (NSNetService sender)
            {
                Console.WriteLine ("published {0}", sender.Name);
            }

            public override void PublishFailure (NSNetService sender, NSDictionary errors)
            {
                Console.WriteLine ("publish failure {0}," + sender.Name);
            }
        }

The browsing is done by calling the NSNetServiceBrowser’s SearchForServices method. I keep a list of NSNetServices as they are discovered in the FoundService callback and register for the AddressResolved event. Similarly, I remove them from the list via ServiceRemoved. Each service is registered to an AddressResolved handler as it is found. The resolve call, something you would do when you want perform actual networking calls with the service, is made here in the UITableViewSource’s RowSelected implementation. When the callback to ServiceAddressResolved happens, you’ll have an NSNetService complete with information that you can use to perform networking as you see fit.

Here’s the code for the controller with the service browsing and resolution:

    public partial class TestViewController : UIViewController
    {
        List _serviceList;
        NSNetServiceBrowser _netBrowser;
        ServicesTableSource _source;

        // constructors omitted for brevity …

        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();
            
            InitNetBrowser ();
        }

        internal void InitNetBrowser ()
        {
            _serviceList = new List ();
            _netBrowser = new NSNetServiceBrowser ();
            
            _source = new ServicesTableSource (this);
            servicesTable.Source = _source;
            
            _netBrowser.SearchForServices ("_testservice._tcp", "");
            
            _netBrowser.FoundService += delegate(object sender, NSNetServiceEventArgs e) {
                
                servicesTextView.Text += "\r\n" + e.Service.Name + " added";
                
                _serviceList.Add (e.Service);                
                e.Service.AddressResolved += ServiceAddressResolved;
                
                //NOTE: could also insert and remove rows in a more fine grained fashion here as well
                servicesTable.ReloadData ();
            };
            
            _netBrowser.ServiceRemoved += delegate(object sender, NSNetServiceEventArgs e) {
                
                servicesTextView.Text += "\r\n" + e.Service.Name + " removed";
                
                var nsService = _serviceList.Single (s => s.Name.Equals (e.Service.Name));
                _serviceList.Remove (nsService);
                servicesTable.ReloadData ();
            };
        }

        void ServiceAddressResolved (object sender, EventArgs e)
        {
            NSNetService ns = sender as NSNetService;
            
            if(ns != null)
                servicesTextView.Text += "\r\n" + ns.Name + " resolved";
            
            // at this point you could use any networking code you like to communicate with the service
        }

        class ServicesTableSource : UITableViewSource
        {
            TestViewController _controller;
            const string SERVICE_CELL_ID = "servicecell";

            public ServicesTableSource (TestViewController controller)
            {
                _controller = controller;
            }

            public override int RowsInSection (UITableView tableview, int section)
            {
                return _controller._serviceList.Count;
            }

            public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
            {
                var serviceCell = tableView.DequeueReusableCell (SERVICE_CELL_ID) ?? new UITableViewCell (UITableViewCellStyle.Value1, SERVICE_CELL_ID);
                
                NSNetService ns = _controller._serviceList[indexPath.Row];
                
                serviceCell.TextLabel.Text = ns.Name;
                
                return serviceCell;
            }
            
            public override void RowSelected (UITableView tableView, NSIndexPath indexPath)
            {
               NSNetService ns = _controller._serviceList[indexPath.Row];
               ns.Resolve(60);
            }
        }
    }

Here’s the app running on the device while another instance is running in the simulator:

You can download the sample project here.

Here’s the short presentation and samples from the talk I gave at the CTDOTNET Code Camp last month.

The samples are available here: http://cid-0486030770596f62.office.live.com/self.aspx/Public/ctcodecamp^_monotouch^_intro.zip

GameKit is a framework Apple created that provides peer to peer Bluetooth networking capability. It is meant for transmitting small messages between devices in close proximity. You can use GameKit on relatively newer iDevices including iPhone 3g, iPod Touch 2nd generation and iPad (and newer versions of each as well). Although it’s called GameKit, as the small messages between nearby devices are well suited to peer to peer gaming scenarios, it can be used for any purpose. For larger data transfer, you need to chunk data into many small messages (similar to what you typically do for an http chunking upload, if you’re familiar with that). I’ll show you a simple example here of using GameKit to create a minimalist chat application, the full source code for which is available at http://github.com/mikebluestein/GameKitChat.

GameKit abstracts all the networking details for you. It even provides the UI for device connectivity via the GKPeerPickerController class. You can also use your own UI as well. Additionally, if you want to support networking other than via Bluetooth, you can do so. GameKit doesn’t add any additional networking capability other than Bluetooth but it does give you the ability to hook in your own networking code (they call it “online mode”) and still take advantage of the common interface.

In MonoTouch GameKit lives under the MonoTouch.GameKit namespace. The main class you work with to use GameKit is the GKSession. The GKPeerPickController and the GKSession together make it very easy to request connections and manage data transfer. Internally these wrap Apple’s Bonjour technology, which is their config free networking stack.

In the example below I created a simple app with a UITextView as the chat log and a UITextField to enter new messages. A UIToolBar houses a single button to launch the peer picker. The pop up dialogs shown are all from the stock UI that you get for free with UIPeerPickerController.

The basic steps are:

– Create a GKSession
– Subscribe to events on the GKSession
  – ConnectionRequest to handle accepting a connection request from a peer
  – ReceiveData to handle incoming data from a peer
– Create a GKPeerPickerController
– Set the type of connection you are supporting on the GKPeerPickerController via its ConnectionTypesMask (nearby for Bluetooth)
– Set the GKPeerPickerController’s delegate (this is where I dismisses the picker in the example)

Here’s a code snippet showing the creation of the example’s GKSession and GKPeerPickerController:

GameKitSession = new GKSession ("com.mikebluestein.gamekitchat", 
                                 UIDevice.CurrentDevice.Name, 
                                 GKSessionMode.Peer);

GameKitSession.ReceiveData += (s, e) => { 
  AddMessage (NSString.FromData (e.Data, 
                       NSStringEncoding.UTF8).ToString ()); };

GameKitSession.ConnectionRequest += (s, e) => { 
  e.Session.AcceptConnection (e.PeerID, IntPtr.Zero); };

GKPeerPickerController peerPickerController = 
  new GKPeerPickerController ();

peerPickerController.Delegate = new PeerPickerDelegate (this);

peerPickerController.ConnectionTypesMask = GKPeerPickerConnectionType.Nearby;

peerPickerController.Show ();

The callback to ReceivedData takes a GKDataReceivedEventArgs that includes an NSData containing the message that was sent by a peer (in this case a text message that they entered in a UITextField). The data is sent via a call to GKSession.SendDataToAllPeers. The PeerPickerDelegate is a subclass of GKPeerPickerControllerDelegate. See the solution for the full implementation. Also, GameKit requires you to use the device for Bluetooth networking as this isn’t supported in the simulator, so you’ll need at least 2 devices. Here’s a demo video of the app running between an iPhone 3g and an iPad:

One other thing worth mentioning is the current GameKit stack also has support for peer-peer voice (think in game voice scenarios) and future versions will add more capabilities as well. The Apple GameKit Programing Guide is a good reference to learn more.