@property (nonatomic, readonly) EAAccessory *accessory in Objective-C

Printer QR Code JIS X 0510 in Objective-C @property (nonatomic, readonly) EAAccessory *accessory

The accessory property returns the reference to the accessory currently associated or attached to this session. This will, of course, in most instances, be the accessory currently connected to the iPhone. There may exist conditions where the accessory returned by session differs from the actual accessory attached to the iPhone. The two

conditions that come to mind are: (1) an accessory is changed without having dropped the original session reference and (2) when Apple allows multiple accessories to be connected to the same iPhone. Let s skip over streams for a moment and talk about the protocolString property of the EASession object.

This property returns the NSString containing the protocol associated with the session. When you create a session, you set the protocolString value as shown in the following statement:

EASession *session = [[EASession alloc] initWithAccessory:accessory forProtocol:protocolString];

Here, you create a reference to an EASession object called session using the standard alloc-init methods. Remember, when using alloc-init, you must release the object somewhere else in the code. For a session, you typically use openSession and closeSession methods within your accessory controller object. One other thing to note about this line of code is that, while you declared the EASession object explicitly (EASession *session) at the start of the statement, you may (and probably normally) want the EASession to be public. In that case, you would declare it in the interface specification for the accessory controller along with any other elements you need to be public such as the reference to the accessory and possibly the protocol string.

@interface CCT01Controller : NSObject <EAAccessoryDelegate>{ EAAccessory *_accessory; EASession *_session; NSString *_protocolString; }

Normally, after you execute the statement above, the first thing to check is whether or not a session was created as in:

if (session) { // do something ... }

If for some reason a valid session was not created, you will need to verify that you have a valid accessory and are using the correct protocolString. If, however, the statement is TRUE, then you need to create the input and output streams that you use to transfer data between your app and the accessory. But before you get to that, you first need to describe streams.

@property (nonatomic, readonly) NSInputStream *inputStream @property (nonatomic, readonly) NSOutputStream *outputStream

Streams are basically what their name implies: a sequence of data that goes from one point to another. Like its watery namesake, your streams travel in one direction: downstream. Therefore, in order to support bi-direction traffic, two data streams are required. From within your frame of reference inside the iPhone application, you create an input stream to handle data coming from the accessory and an output stream to handle the data you send to the accessory. You use the Cocoa classes NSInputStream and NSOutputStream, both of which are derived from NSStream. Stream objects also have properties associated with them. Most properties have to do with network security and configuration, and as such will not be discussed here. Most importantly, a stream object has a delegate associated with it. The delegate object, which in your case will be the accessory controller object, must support the stream:handleEvent: method. Apple has provided a prototype implementation for dealing with events from streams. Essentially, whenever something happens in regards to a stream, this method is called. Depending on what eventCode was received you take one of several actions. But first, you need to create the streams and that is done in three steps for each (input and output) stream. This is where you use the if (session) statement.

if (session) { [[session inputStream] setDelegate:self]; [[session inputStream] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; [[session inputStream] open]; [[session outputStream] setDelegate:self]; [[session outputStream] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; [[session outputStream] open]; } else { NSLog(@"creating session failed"); }

Most likely, you will include the preceding code within your method that handles the opening of the EASession. If you determine that you have a valid session, then you follow three steps for each stream: Set the stream delegate (usually to self). Schedule the stream to execute within a run loop. Open the stream. Once these three steps are completed, you now begin to receive calls to the stream:handleEvent: method.