how to create barcode in vb net 2008 11: Properties in Objective-C

Encoding QR Code in Objective-C 11: Properties

CHAPTER 11: Properties
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NSMutableArray *tires; Engine *engine; } @property (copy) NSString *name; @property (retain) Engine *engine;
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and then change the synthesize directive:
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@synthesize name = appellation;
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The compiler will still create -setName: and -name but will use the appellation instance variable inside of their implementations. But when you compile, you see a couple of errors. You may recall that we directly accessed the name instance variable, which has been changed. We can choose to do a search and replace on the name, or we can change direct ivar access to use accessors instead. In init, change
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name = @"Car";
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self.name = @"Car";
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What s that self-dot-name business It s a bit of disambiguation to let the compiler know that we want to vector through the accessors. If we just use a naked name, the compiler assumes that we re directly modifying an instance variable. To go through the accessors, we can write [self setName:@"Car"]. Remember that the dot is just shorthand for making this exact same call, so self.name = @"Car" is just another way of saying the same thing. In dealloc, we ll pull a nifty trick:
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self.name = nil;
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This line says to call setName: with an argument of nil. The generated accessor method will automatically release the previous name and replace the name with nil. This method accomplishes the work of releasing the memory for the name. Of course, we could just release name to clean up the memory. If you re clearing out a property outside of dealloc, using the assign to nil trick will set the property value to nil, keeping us from having a dangling reference to memory that might have been freed. Finally, -description needs its first NSLog fixed:
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NSLog (@"%@ has:", self.name);
CHAPTER 11: Properties
Now, we can rename appellation to something else, like nickname or moniker. We just need to change the instance variable name and the name used in @synthesize.
Read-Only About It
You might have an object with an attribute that is read-only. This attribute might be a value that s computed on the fly, like the surface area of a banana, or might be one that you want other objects to read but not change, like your driver s license number. You can code for these situations with more attributes on @property. By default, properties are mutable: you can read and write them. Properties have a readwrite attribute you can use. Since it s the default, you won t usually use it, but it s there if you need it and you want to make your intentions clear. We could have used readwrite in Car.h:
@property (readwrite, copy) NSString *name; @property (readwrite, retain) Engine *engine;
But we didn t, because we generally want to stamp out and abolish and get rid of redundancy and repetition and saying the same thing over again. Returning to our read-only property discussion, let s say we have a property, such as our license number or shoe size, that we don t want to be changed by anybody. We can use the readonly attribute on @property. An example class would be something like this:
@interface Me : NSObject { float shoeSize; NSString *licenseNumber; } @property (readonly) float shoeSize; @property (readonly) NSString *licenseNumber; @end
When the compiler sees that @property is readonly, it generates a getter but not a setter for that attribute. Users of Me can call -shoeSize and -licenseNumber, but if you try to call -setShoeSize:, the compiler will complain. You ll get the same behavior when using dot notation.
Alas, Properties Don t Do Everything
You ll notice we didn t convert Car s tire methods to properties:
- (void) setTire: (Tire *) tire atIndex: (int) index; - (Tire *) tireAtIndex: (int) index;
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