C# 4 and .NET 4

Building P2P applications ❘ 1353
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PeerPresenceStatus.Busy — The peer is busy.
PeerPresenceStatus.Idle — The peer isn’t active.
PeerPresenceStatus.Offline — The peer is offline.
PeerPresenceStatus.Online — The peer is online and available.
PeerPresenceStatus.OnThePhone — The peer is busy with a phone call.
PeerPresenceStatus.OutToLunch — The peer is away, but will be back after lunch.
Discovering Peers
You can obtain a list of peers near you if you are logged in to the link local cloud. You do this by using the
PeerCollaboration.GetPeersNearMe() method. This returns a PeerNearMeCollection object containing
PeerNearMe objects.
You can use the Nickname property of PeerNearMe to obtain the name of a peer, IsOnline, to determine
whether the peer is online, and (for lower-level operations) the PeerEndpoints property to determine endpoints
related to the peer. PeerEndPoints is also necessary if you want to find out the online status of a
PeerNearMe. You can pass an endpoint to the GetPresenceInfo() method to obtain a PeerPresenceInfo
object, as described in the previous section.
Managing Contacts and Detecting Peer Presence
Contacts are a way in which you can remember peers. You can add a peer discovered through the People
Near Me service and from then onward you can connect to them whenever you are both online. You can
connect to a contact through link local or global clouds (assuming you have IPv6 connectivity to the
Internet).
You can add a contact from a peer that you have discovered by calling the PeerNearMe
.AddToContactManager() method. When you call this method you can choose to associate a display name,
nickname, and e-mail address with the contact. Typically, though, you will manage contacts by using the
ContactManager class.
However you manipulate contacts, you will be dealing with PeerContact objects. PeerContact, like
PeerNearMe, inherits from the abstract Peer base class. PeerContact has more properties and methods
than PeerNearMe. PeerContact includes DisplayName and EmailAddress properties that further describe
a PNM peer, for example. Another difference between these two types is that PeerContact has a more
explicit relationship with the System.Net.PeerToPeer.PeerName class. You can get a PeerName from a
PeerContact through the PeerContact.PeerName property. After you have done this you can proceed to
use techniques you looked at earlier to communicate with any endpoints the PeerName exposes.
Information about the local peer is also accessible through the ContactManager class, through the static
ContactManager.LocalContact property. This gets you a PeerContact property with details of the
local peer.
You can add PeerNearMe objects to the local list of contacts by using either the ContactManager
.CreateContact() or CreateContactAsync() method, or PeerName objects by using the GetContact()
method. You can remove contacts represented by a PeerNearMe or PeerName object with the
DeleteContact() method.
Finally, there are events that you can handle to respond to changes to contacts. For example, you can use the
PresenceChanged event to respond to changes of presence for any contacts known by the ContactManager.
sample application
There is a second sample application in the downloadable code for this chapter that illustrates the use of
classes in the System.Net.PeerToPeer.Collaboration namespace. This application is similar to the other
example, but much simpler. You need two computers that can both sign in to the PNM server to see this
application in action, because it enumerates and displays PNM peers from the local subnet.
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