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

Experience report

The Desktop Team, in the University’s Information Servicesdepartment have asked for feedback from you regarding yourexperiences (good or bad!) with Xcode in the Main Library IS OpenAccess Lab.

This will help inform their plans for future academic years.

What has been your experience?


Programming with arrays in Objective-C

shot 2012-11-01 at 15.49.03.png


Inspecting an array

shot 2012-11-01 at 15.48.54.png


The XML representation

shot 2012-11-01 at 15.49.50.png


Sorting an array

shot 2012-11-02 at 09.12.09.png


The sorted array

shot 2012-11-01 at 15.51.38.png


The output in the console

shot 2012-11-01 at 15.57.19.png


Everything OK? What about “Build and Analyze”?

shot 2012-11-02 at 09.02.59.png


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];

NSArray *sortedArray =

[myArray sortedArrayUsingSelector:@selector(

caseInsensitiveCompare:)];

[sortedArray writeToFile:@"sortedArray.plist"

atomically:YES];

for(NSString * myStr in sortedArray) {

NSLog(@"---- %@", myStr);

}

[pool drain];

return 0;

}


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 containdifferent kinds of objects.

The nil value at the end is a terminator, signalling the end of thearray.

You can release an object as soon as you add it to an array becausethe array allocates its own memory for the object by calling retain onall objects which are added to it.

arrayWithObjects auto releases from memory so you do not haveto release the array yourself.

If we replace [NSArray alloc] initWithObjects witharrayWithObjects then this should solve our memory leak.


“Build and Analyze” finds no potential leaks now

shot 2012-11-02 at 09.18.34.png


Mutable arrays

NSArray objects are not mutable so we cannot update their contents.

To have an array which we can update we should useNSMutableArray.


Declaring and using mutable arrays

shot 2012-11-02 at 09.59.55.png


Output from the program

shot 2012-11-02 at 10.00.07.png


arrays in objective-c

Education

arrays arrays

handling arrays

generic arrays

mutable arrays nsarray

sortedarray writetofile

myarray writetofile

nsarray allocinitwithobjects

nsarray alloc initwithobjects