vb.net barcode printing 17: Future Paths in Java

Encoder Data Matrix in Java 17: Future Paths

CHAPTER 17: Future Paths
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Observing Notifications Using Blocks
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We realize that we just threw notifications at you a few pages ago, but guess what: Apple s already taken the block concept and applied it to the NSNotification class as well, which boasts a new method in Snow Leopard that lets you specify a block rather than a selector, like this:
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[[NSNotificationCenter defaultCenter] addObserverForName:DATA_RECEIVED object:nil queue:nil usingBlock:^(NSNotification *notification){ NSLog(@"received notification: %@", notification); }];
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This is cool in a couple of ways. For one thing, it frees you from the burden of creating a method for your notification-handling code, letting you instead put it inline with the code that s setting it up, which can make your code easier to read. The other cool thing, which is true of all blocks, is that because the block you create picks up its context from the location it s defined in, it has access to not only instance variables, but also local variables defined earlier in the same method. That means that you can defer access to some values until a later time, without needing to explicitly put them into instance variables or pass them along in some other manual way.
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Another use of blocks that Apple has added to Cocoa is NSArray s indexesOfObjectsPassingTest: method. This method lets you declare a block that will examine an object, and based on your own criteria determine whether it should be included in the set of indexes that comes out (which can in turn be used to extract the successes from the original array. For example, assuming you have an array of people, you can find all the people named Bob like this:
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NSArray *people; // <- assume this exists NSIndexSet *bobIndexes = [people indexesOfObjectsPassingTest: BOOL ^(id obj, NSUInteger idx, BOOL *stop){ return [obj.firstName isEqual:@"Bob"]; }]; NSArray *bobs = [people objectsAtIndexes:bobIndexes];
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Although the use of blocks may seem tricky at first, after a while they become second nature, and once you get started, you ll probably find more and more ways to use them. They are a really important tool for every Cocoa programmer moving forward.
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As much as some of us love Objective-C, it s not the only game in town, and some people would rather use another language for developing Cocoa apps. Maybe you have a particular code library you want to make use of, or maybe you just prefer some other language. The good news is that there are some languages out there that can interface
CHAPTER 17: Future Paths
with Objective-C well enough to allow for some Cocoa development, through the use of what s called a bridge between the other language and Objective-C. The bad news, for some people at least, is that two of the biggest, most popular languages, C++ and Java, aren t among them. You may be wondering why not. Well, without getting too deep: C++ and Java are just too inflexible. They don t have the sort of runtime introspection capability that s required for fully interfacing with complex Objective-C class libraries like Cocoa. Maybe, technically, Java has got what it takes. In fact, Apple included a Java bridge for building Cocoa apps in the first several versions of Mac OS X. But the fact that programmers weren t lining up at the gates to use it, combined with the technical challenge of implementing and maintaining the Java bridge, just made it not worthwhile for them, and Apple abandoned the project several years ago. And because you can actually combine Objective-C and C++ together in the form of Objective-C++, the need for bridging there is somewhat reduced. There are some real limitations there. You can t, for instance, implement an Objective-C delegate in the form of a C++ class, so you ll need to create some glue classes, typically paired up across the border (one C++, one Objective-C) that are each able to deal with their own world and translate things for one another. It works, but believe me, that sort of code is not much fun to write or maintain. Back on the good news side of things, some of the languages whose usage is still increasing year-by-year, such as Python and Ruby, have solid, working bridges that let you do real Cocoa work with them.
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