how to print barcode in vb.net 2008 Peer-to-peer connections using Game Kit in Objective-C

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Peer-to-peer connections using Game Kit
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15.2.2 Implementing the GKSessionDelegate methods
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To send and receive data with Game Kit, you must implement the delegate methods for GKSession. These methods provide a nice high-level interface for you to use to send data over the network. Your class must also implement the GKSessionDelegate interface. Your application should implement four delegate methods, outlined in table 15.2.
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Table 15.2
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GKSessionDelegate methods
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Delegate method Description Called any time a peer changes state. The five possible states are GKPeerStateAvailable, GKPeerStateUnavailable, GKPeerStateConnected, GKPeerStateDisconnected, and GKPeerStateConnecting. Called when a peer wants to connect. Apple s documentation suggests that this method can be ignored if you re using the built-in peer picker. Called when a connection error occurs. This method can also be ignored if you re using Apple s peer picker, because it automatically handles it and displays a UIAlertView. Called when an unrecoverable error happens. In this method, you should disconnect all peers and notify the user.
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session:peer:didChangeState:
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session:didReceiveConnectionRequestFromPeer:
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session:connectionWithPeerFailed:withError:
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session:didFailWithError:
For most applications, you only need to implement the didChangeState method. The others are handled automatically. The didChangeState method is important for keeping track of all the peers connected. When a peer connects, you should maintain a reference to it by adding it to a global peers array. That way, when it comes time to send data to it, you ll know where to send it. When a peer leaves, you should remove it from the peer array. Listing 15.2 details a simple way to implement this method.
Listing 15.2 Implementing the didChangeState delegate method
- (void)session:(GKSession *)session peer:(NSString *)peerID didChangeState:(GKPeerConnectionState)state { switch (state) Adds peer to { peers list case GKPeerStateConnected: [peers addObject:peerID]; [chatTextArea setText:[NSString stringWithFormat: @"%@ has joined the chat.\n",[session displayName]]]; break; case GKPeerStateDisconnected: Removes peer [peers removeObject:peerID];
from peers list
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Creating peer-to-peer applications using the peer picker
NSString * text = [chatTextArea text]; [chatTextArea setText:[NSString stringWithFormat: @"%@\n%@ has left the chat.\n",text, [session displayName]]]; break; } }
As you can see, this method is relatively simple to implement. You determine the state of the peer with a simple case statement. You add code to detect the two most important states, GKPeerStateConnected and GKPeerStateDisconnected. You should also handle the other states as noted in table 15.2. In the event that a peer connects, you want to make sure to maintain a reference to that peer s ID B. You do this by adding the ID to an array of peer IDs. You ll later use this ID to send data to that specific peer. Note that you update the text of a UITextView to notify the user that a given peer has connected. You can also do this with a UIAlertView or else start the game if you re creating a multiplayer game. The session object contains quite a bit of information about the incoming session. The most important property for the sake of the chat application is the displayName field. This lets you display the unique name of a given peer. As you can imagine, almost any multiuser application can benefit from this field. Finally, you handle the case where a peer disconnects C. In the event of a disconnection, you want to remove the peer ID from the array. This ensures that you don t waste any resources sending data to it. Again, you notify the user that the peer has disconnected. Now that you ve implemented the delegate methods, you need a way to send and receive data.
15.2.3 Sending and receiving data between peers
When you re sending data from one peer to another, keep in mind that everything you send must be converted to NSData. Every one of Apple s built-in objects supports this conversion. You can even convert custom objects to NSData using the NSKeyedArchiver class. The type of data you send over the network is highly dependent on what your application does. For example, if you re creating a real-time game that sends a lot of data quickly, then you probably don t want to send complete objects. In this case, you re better off sending low-level data structures such as a struct. Although this method is much faster, it requires that you have a good understanding of some low-level C code. You ll see more about sending structs over the network in the next section. On the other hand, if your application doesn t rely so much on speed, you can send high-level objects and greatly reduce the complexity of your application. For the simple chat application, you convert strings to NSData, send them over the network, and convert them back into strings. Listing 15.3 shows how to implement the receiveData method as well as the send method.
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