c# create barcode 2: EAAccessory Framework in Objective-C

Creator QR Code in Objective-C 2: EAAccessory Framework

CHAPTER 2: EAAccessory Framework
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TIP: Remember the rule: One session per EAAccessoryDelegate protocol per accessory. The first step for each stream is to set the delegate to this object in which the code resides. This causes the delegate method calls generated by the input and output streams to be handled within this object. The second line of code for both the input stream and output stream sets the events to happen within the current run loop. You have the ability to set this to a different run loop, which you might do if there were a lot of user interface interactions happening in the main run loop; you would set this up to happen in a different thread and a different run loop. To keep things simple, you will be using the default run loop. NOTE: For more detailed information on run loops see the Threading Programming Guide in the iPhone OS Reference Library. Finally, you open the stream to begin sending and receiving data. Once the streams have been opened, the stream:handleEvent: method shown below will handle events from both the input and output stream. Why does this statement handle both input and output streams It does so because you set the delegate to be self for both the input and output streams in the previous code snippet. When any event of interest happens in either stream, this method gets called. Note the NSStreamEventOpenCompleted, NSStreamEventErrorOccurred, and NSStreamEventEndOccurred cases; these would occur for both the input and output stream and should be handled accordingly. The event codes of most interest to us, NSStreamEventHasBytesAvailable and NSStreamEventHasSpaceAvailable refer to the input and output streams respectively. As is mostly obvious, the first case means that the accessory has sent data to the iPhone and it is ready to be read. The second case means that there is space available in the stream to send data to the accessory. To deal with these two cases, either the _writeData or _readData are called. I will cover more about what happens in these routines when I start discussing design patterns.
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CHAPTER 2: EAAccessory Framework
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NOTE: Apple uses the underscore syntax (_writeData, _readData) in their EA Accessory Reference material on occasion. In general, you put an underscore in front of a method name to refer to a local method where you might also have methods with the same name elsewhere. For example, Apple uses writeData as a public method name in their example accessory controller, but then use _writeData to refer to a different method within the object acting as the accessory controller. Does this mean you ll see two writeData methods in the accessory controller object Yes! Both _writeData and writeData will be found. Though slightly more confusing, you will follow this trend in order to track more closely with Apple s reference material.
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- (void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode { switch (eventCode) { case NSStreamEventNone: NSLog(@"stream %@ event none", aStream); break; case NSStreamEventOpenCompleted: // Do something for Open Completed event break; case NSStreamEventHasBytesAvailable: NSLog(@"stream %@ event bytes available", aStream); [self _readData]; break; case NSStreamEventHasSpaceAvailable: NSLog(@"stream %@ event space available", aStream); [self _writeData]; break; case NSStreamEventErrorOccurred: // Do something for Error event break; case NSStreamEventEndEncountered: // Do something for End event break; default: break; } }
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Summary
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This chapter covered all the details needed to understand Apple s EAAccessory framework. The EAAccessory framework is a directory that contains the accessory runtime library and more. Apple uses EAAccessory, which seems to mean External Accessory Accessory , even though it s double booking the Accessory term. I also discussed the difference between the two uses of protocol. In creating EAAccessory programs, you used both the <EAAccessoryDelegate> protocol as well as the protocol (communications rules) that defines how data pass over the input and output streams between the iPhone and the accessory. You also broke down some sample protocols into their constituent parts such as command byte, status byte, and
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