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Now you understand that the EAAccessoryManager s purpose in life is to inform of when an accessory is connected or disconnected. And, you know that this information is provided to you via the Notification center. Let s again look at the code from the previous section.
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[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(readerConnected:) name:EAAccessoryDidConnectNotification object:nil];
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CHAPTER 2: EAAccessory Framework
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[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(readerDisconnected:) name:EAAccessoryDidDisconnectNotification object:nil]; [[EAAccessoryManager sharedAccessoryManager] registerForLocalNotifications];
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As a quick reminder, the first two statements in this code snippet direct all the notifications for when an accessory is connected or disconnected to kick off two methods (readerConnected and readerDisconnected) within the object that contains the code. In the last statement, you see that you must register with the EAAccessoryManager instance for the accessory connected notifications. The EAAccessory Framework s EAAccessoryManager class provides the following two methods to start and stop receiving notifications:
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- registerForLocalNotifications - unregisterForLocalNotifications
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Our app calls the registerForLocalNotifications method to be notified when an accessory is connected or disconnected. The reason you need to use this is that the notification system does not send EAAccessory notifications (connected or disconnected) automatically. So, in the code segment above, if you didn t include the third line of code, you would not receive the connected or disconnected notifications. Call this statement (registerForLocalNotifications) once, usually within the viewDidLoad of our primary view controller. The notification observers (the first two statements of the code segment) can be called either before (as is shown) or after calling registerForLocalNotifications. Call the method unregisterForLocalNotifications when your application is ready to terminate (applicationDidTerminate) or if you are no longer interested in receiving accessory-related notifications.
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Available Accessories from Accessory Manager
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The last topic in this section discussing the EAAccessoryManager shows how you actually get the list of connected accessories. This is done by using the connectedAccessories property. In the following code snippet, you see one way to use this property.
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EAAccessory *connectedAccessory = [[[EAAccessoryManager sharedAccessoryManager] connectedAccessories] objectAtIndex:0];
In fact, this statement provides a nice little overview of several of the subjects I ve just covered. First, to the left of the = assignment, you declare a pointer to an EAAccessory object that you call connectedAccessory. This will be the reference to the accessory you will work with in your code. Next, fresh from the previous section, you see that you have returned the instance of the accessory manager to which you query the property connectedAccessories. This
CHAPTER 2: EAAccessory Framework
complex statement returns the NSArray of accessories. Finally, you return the 1st object located at index zero (remember that there is likely only one object in the array) to be assigned to the connectedAccessory reference. In the Pong game that you will build later, you may find that you use the connectedAccessories property in a couple of different ways. In one such case, you might use the following statement to simply assign the list of connected accessories to our own NSArray object.
NSArray accessoryList = [[NSMutableArray alloc] initWithArray:[[EAAccessoryManager sharedAccessoryManager] connectedAccessories]];
You may use this form within your code if you wish to maintain a reference to the list of accessories returned from the shared accessory manager. This format will be more useful when Apple begins permitting multiple accessory connections. You see another use for the connectedAccessories property in the following conditional statement. Here, if there are any accessories connected no matter what they are, you log a message to the console saying as much. A good time to use this format might be when you load your view controller that interacts with the accessory.
if ([[EAAccessoryManager sharedAccessoryManager] connectedAccessories]) NSLog(@"there is already a connected accessory");
You will explore these structures in more depth in the following chapter when I discuss design patterns.
EASession
As I stated earlier, the EASession class creates the communications channel between the app and the accessory. So what is a session Basically, a session abstractly represents the fact that we have an accessory attached and that you can talk to it using a protocol. And by protocol here, I mean the second definition I talked about earlier the rules governing the message structure between the app and the accessory. Your app generally references the session at three major times: (1) when you create the session, (2) when you open the session, and (3) when you close the session. You generally close the session in our dealloc routine in the accessory controller object. The EASession object includes four properties: accessory, inputStream, outputStream, and protocolString. The astute observer will note that the protocolString property here is singular whereas for the EAAccessory object it was an NSArray and therefore plural. This reinforces the fact that while an accessory may be able to use several different protocols, a session uses a specific protocol. Thus, you could have, say, a diagnostic session using one protocol and an operations session that uses a different protocol.
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