.net barcode generator suite 2: Getting Started in Objective-C

Generator ECC200 in Objective-C 2: Getting Started

CHAPTER 2: Getting Started
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The magic is that addChild adds the object to a collection, in this case a CCArray that s similar to the NSMutableArray of the iPhone SDK, but faster. The CCArray and the NSMutableArray and any other iPhone SDK collection automatically send a retain message to any object added to them, and send a release message to any object removed from the collection. Thus the object stays around and remains valid and can be accessed at a later time, yet it will automatically be released after it has been removed from the collection. What you should keep in mind is that managing memory for cocos2d objects is best done as I described here. You may run into other developers who say that autorelease is bad or slow and shouldn t be used. Don t give in to them. NOTE: The Apple developer documentation recommends reducing the number of autorelease objects. Most cocos2d objects, however, are created as autorelease objects. It makes memory management much easier, as I ve shown. If you start using alloc/init and release for every cocos2d object, you ll get yourself into a lot of pain for little to no benefit. That isn t to say that you ll never use alloc/init; it does have its uses and is sometimes even required. But for cocos2d objects, you should rely on using the static autorelease initializers. Autorelease objects have only one caveat, and that s that their memory is in use until the game advances by one frame. This means if you create a lot of throw-away autorelease objects every frame, you might be wasting memory. But that s actually a rare occurrence. This concludes my quick primer on cocos2d memory management. Memory management in the Objective-C world is governed by simple rules: If you own (alloc, copy, or retain) an object, you must release it later If you send autorelease to an object, you must not release it For a more in-depth discussion of memory management, refer to Apple s Memory Management Programming Guide (http://developer.apple.com/iphone/library/documentation/Cocoa/Conceptual/Memor yMgmt/MemoryMgmt.html).
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Changing the World
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What good is a template project like HelloWorld if I don t have you tinker with it at least a little I ll have you change the world by touching it! How s that for a start First you ll make two changes to the init method to enable touch input and to use a tag value to retrieve the label at a later point. The changes are highlighted in Listing 2 3.
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CHAPTER 2: Getting Started
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Listing 2 3. Enabling Touch and Gaining Access to the Label Object -(id) init { if ((self = [super init])) { // create and initialize a label CCLabel* label = [CCLabel labelWithString:@"Hello World" fontName:@"Marker Felt" fontSize:64]; // get the window (screen) size from CCDirector CGSize size = [[CCDirector sharedDirector] winSize]; // position the label at the center of the screen label.position = CGPointMake(size.width / 2, size.height / 2); // add the label as a child to this Layer [self addChild: label]; // our label needs a tag so we can find it later on // you can pick any arbitrary number label.tag = 13; // must be enabled if you want to receive touch events! self.isTouchEnabled = YES; } return self; }
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The label object gets 13 assigned to its tag property. Now why did you do that I know, I told you to but I must have had a reason, right In the previous section, I explained that s how you can later access a child object of your class you can refer to it by its tag. The tag number is completely arbitrary, other than that it must be a positive number and every object should have its own tag number, so there aren t two with the same number or you couldn t tell which you d be retrieving. TIP: Instead of using magic numbers like 13 as tag values, you should get in the habit of defining constants to use with tags. You ll have a hard time remembering what tag number 13 stands for, compared to writing a meaningful variable name like kTagForLabel. I ll get to this in 5. Secondly, self.isTouchEnabled is set to YES. This is a property of the CCLayer class and tells it that you want to receive touch messages. Only then will the method ccTouchesBegan be called:
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-(void) ccTouchesBegan:(NSSet*)touches withEvent:(UIEvent*)event; { CCLabel* label = (CCLabel*)[self getChildByTag:13]; label.scale = CCRANDOM_0_1(); }
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By using [self getChildByTag:13], you can access the CCLabel object by its tag property, which you assigned in the init method. You can then use the label as usual. In this case, we use cocos2d s handy CCRANDOM_0_1() macro to change the label s scale
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