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

Generation QR Code ISO/IEC18004 in Objective-C 2: EAAccessory Framework

CHAPTER 2: EAAccessory Framework
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The class also defines the three public properties: _accessory, _session, and _protocolString. I will discuss these more in-depth later in this chapter when we talk about EASession. Let s pause for a moment here to discuss delegates just a bit. Having previously written at least a couple iPhone apps, you ve certainly come across delegation. When you read about delegation, the sentences all seem to make sense on their own, but a lot of people come away with an uneasy feeling that they just haven t gotten it completely. Starting from the top, you build your program by creating a set of objects with properties and methods. We all get that; it s basic object-oriented programming. And, as discussed before, since you re doing embedded systems programming, your objects will generally respond to outside stimulus; either a loop within your code polls something until it changes, or maybe an external interrupt changes and calls a method of your object. A delegate is nothing more than one of those objects within the set of objects that make up your program, or, specifically, your application. You might have view-controller objects, tab-bar controller objects, and even special, unique objects that you ve made up. Because we tend, as developers, to get caught up in the details, it is easy to forget that your set of objects is also an object in itself. Together they form a UIApplication object. Now, it s easy to see that this higher-level object, the UIApplication, also contains properties and methods. For example, there is a method called applicationDidFinishLaunching that is called when the application has, well, finished launching. But you never defined or subclassed a UIApplication object, correct What you did was declare one of your objects to be the application delegate. Typically, most iPhone programming tutorials will create something that ends in AppDelegate and implements this ApplicationDelegate protocol and is where you find such good stuff as applicationDidFinishLaunching. In essence, you create an application delegate to handle all the stuff that centers on your application: the starting, the stopping, the memory warnings, etc. A delegate is, therefore, the object you create (or code) that handles the work of some other object such as UIApplication, or, as is the subject of this book, the EAAccessory. You create an object, the delegate object, to handle all the work that is created by your all-encompassing UIApplication or your accessory object, UIAccessory. Think of the delegate as the clerk you talk to when you go to the DMV to renew your license. You don t directly interface with the DMV system, but instead with a delegate of that system. Continuing with our discussion of the properties associated with accessories, several of these provide specific details of the actual hardware itself. The read-only firmwareRevision property provides an NSString that represents what version of firmware resides in the processor that controls the accessory. Remember, the accessory must handle identification and authentication with the iPhone s OS even before it can talk to your application.
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@property (nonatomic, readonly) NSString *firmwareRevision
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CHAPTER 2: EAAccessory Framework
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Prudence suggests that a cautious app developer be aware of the firmwareRevision and other detailed properties of the accessory to assure continued compatibility between app and accessory. For example, a newer firmware revision may indicate support within the accessory s protocol structure, for additional commands or status fields. That is, a newer, higher firmware revision may provide more details than an initial release of an accessory. Similar to firmwareRevision, the hardwareRevision property gives the app developer important, up-to-date information about the hardware accessory attached to the iPhone. As the development of iPhone accessories is currently in its infancy, these attached devices may change frequently in the early stages of the program. Bugs will be fixed, features added, and changes may be made to accommodate revisions in the specifications from Apple.
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