Arrays in Objective-C

Computer Science Large Practical:

Arrays in Objective-C

Stephen Gilmore

School of Informatics

Friday 2nd November, 2012

Stephen Gilmore (School of Informatics) Computer Science Large Practical Friday 2nd November, 2012 1 / 16

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Programming with arrays in Objective-C


Inspecting an array


The XML representation


Sorting an array


The sorted array


The output in the console


Everything OK? What about “Build and Analyze”?


Handling arrays (1/2)
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc]
init];

NSLog(@"Hello, arrays!");

NSArray * myArray = [[NSArray alloc]
initWithObjects:@"foo",@"bar",@"baz",nil];

for(NSString * myStr in myArray) {
NSLog(@"-- %@", myStr);
}

[myArray writeToFile:@"myArray.plist" atomically:YES];


Handling arrays (2/2)

NSArray *sortedArray = [myArray
sortedArrayUsingSelector:@selector(
caseInsensitiveCompare:)];

[sortedArray writeToFile:@"sortedArray.plist"
atomically:YES];

for(NSString * myStr in sortedArray) {
NSLog(@"---- %@", myStr);
}

[pool drain];
return 0;
}


Object allocation and arrays

Arrays in Objective-C are not generic arrays: they can contain
diﬀerent kinds of objects.
The nil value at the end is a terminator, signalling the end of the
array.
You can release an object as soon as you add it to an array because
the array allocates its own memory for the object by calling retain on
all objects which are added to it.
arrayWithObjects auto releases from memory so you do not have
to release the array yourself.
If we replace [NSArray alloc] initWithObjects with
arrayWithObjects then this should solve our memory leak.


“Build and Analyze” ﬁnds no potential leaks now


Mutable arrays

NSArray objects are not mutable so we cannot update their contents.
To have an array which we can update we should use
NSMutableArray.


Declaring and using mutable arrays


Output from the program


Arrays in Objective-C

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