8: Some Foundation Framework Classes in Objective-C

Painting QR-Code in Objective-C 8: Some Foundation Framework Classes

8: Some Foundation Framework Classes
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The NSArray and NSMutableArray can only hold Objective-C objects, and cannot hold C primitives, or C constructs such as structs But that is where the Objective-C wrapper classes are useful If you wish to store a primitive in an NSArray or NSMutableArray, simply store the primitive in the wrapper class before adding it to the array
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NSNumber * myAge = [[NSNumber alloc] initWithInt:41]; [myFamilyAgesArray addObject:myAge];
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Initializing an Array
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Arrays provide several convenience constructors for creating an NSArray One convenience constructor that you use often is the arrayWithObjects: method
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NSArray * myArray = [NSArray arrayWithObjects: @"A", @"B", @"C",nil];
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This method takes an object list, terminated by nil, and creates a new array that contains the objects The nil value indicates the array s end; however, it is not included as part of the array In the preceding code snippet, the array s length is 3; nil is excluded Rather than using the arrayWithObjects: convenience method, you could have allocated the array and then initialized it
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NSArray * myArray = [[NSArray alloc] initWithObjects: @"A", @"B", @"C", nil];
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Other convenience constructors you might use to create an array include the arrayWithArray:, arrayWithContentsOfFile:, arrayWithContents OfURL:, arrayWithObject:, arrayWithObjects:, and arrayWithObjects: count: methods As with most other Foundation framework classes, each of these convenience constructors have a corresponding init method if you prefer to manage memory yourself by allocating the array and then initializing it
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Remember, if you use a convenience constructor, the convenience constructor adds the object instance created to the autorelease pool The runtime, not you, manages these objects life cycle If you allocate and then initialize the object, you must manage the object s life cycle If you wish to manage an object s lifetime that was created using a convenience constructor, then you must explicitly call retain on the object But note, if you set a property to an object created using a convenience constructor you are calling retain, making this note moot For instance, the following line retains the string even though you use a convenience constructor, assuming myString is a property with the retain attribute in its @property compiler directive foomyString = [NSString stringWithString:"A Test"];
Objective-C for iPhone Developers: A Beginner s Guide
Initializing a Mutable Array
The NSArray is immutable Once initialized, you cannot modify it In contrast, the NSMutableArray allows modifying an array after creating it Because it allows adding and removing objects from the array, the NSMutableArray has another convenience method named arrayWithCapacity: This method allows creating a mutable array and allocating space in advance for a given number of objects to be added to the array
NSMutableArray * myArray = [NSMutableArray arrayWithCapacity:3];
Note that the array in the preceding code snippet is not limited to three objects The arrayWithCapacity: method allocates enough space for three objects; however, you can add more objects if needed Moreover, note that you are not required to use the arrayWithCapacity: method when creating an NSMutableArray instance; any of the other NSArray convenience constructors or init methods work The arrayWithCapacity: method is simply more efficient by allocating the needed space when created When adding objects later, the runtime isn t required to allocate the space for the objects
Adding, Removing, and Replacing Objects
When using an NSMutableArray, you can add, remove, and replace objects that are in the array For instance, the addObject: and insertObject:atIndex: methods allow adding an object, the removeObjectAtIndex: method allows removing an object at a location in an array, and the replaceObject:atIndex: method allows replacing an object
Try This
Using an NSMutableArray
1 Create a new Command Line Foundation Tool unnamed MutableArrayExample 2 Create a new class called Foo and add an NSString as a property (Listings 8-3
and 8-4)
3 Modify MutableArrayExamplem as in Listing 8-5 4 Build and Run the application Listing 8-6 contains the debugger console logging
Listing 8-3
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