Collections. Fall, Prof. Massimiliano "Max" Pala

Transcription

1 Collections Fall, 2012 Prof. Massimiliano "Max" Pala

2 Overview Arrays Copy and Deep Copy Sets Dictionaries Examples

3 Arrays Two Classes NSArray and NSMutableArray (subclass of NSArray) int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoReleasePool alloc] init]; Person *a = [[Person alloc] init]; Person *b = [[Person alloc] init]; NSArray *arr1 = [[NSArray arraywithobjects:a, b, c, d, nil] autorelease]; for (id object in arr1){ NSLog(@"Object = %@", object) NSInteger counter = 0; for ( counter = 0; counter < [arr1 count]; counter++) {. [pool release]; [a release]; [b release]; [c release]; [d release]; return 0; ;

4 Arrays (cont.)

5 Arrays (cont.) int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; Person *a = [[Person alloc] init]; Person *b = [[Person alloc] init]; NSArray *arr1 = [[NSArray arraywithobjects:a, b, c, d, nil] autorelease]; NSArray *arr2 = [arr1 copy]; Person *aperson = [arr1 objectatindex:0]; aperson.name Name"; aperson.address Address"; ; [arr2 release]; // Since we copied it, we release it! [pool release]; [a release]; [b release]; [c release]; [d release]; return 0;

6 Arrays (cont.)

7 Mutable Arrays Allow dynamic manipulation of objects addobject removeobject Adding an object will increment the reference count Removing an object will send a release message to the object When copying, the new array is distinct from the original one Objects are still the same

8 Mutable Arrays int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; Person *a = [[Person alloc] init]; NSArray *arr1 = [[NSArray arraywithobjects:a, b, c, d, nil] autorelease]; NSMutableArray *arr2 = [arr1 mutablecopy]; Person *newperson = [[Person alloc] init]; [arr2 addobject:newperson]; [arr2 removeobject:a]; [pool release]; [a release]; ; [newperson release]; return 0;

9 Mutable Arrays (cont.)

10 Deep Copy Shallow copies is the default behavior for NSArray and NSMutableArray A deep copy is a copy that is independent of the original The object has to implement the NSCopying protocol 1. Your class must be descendent of NSObject and adopt the NSCopying protocol 2. It must implement copywithzone: method. A call to the super's copywithzone: should be the first statement. The returned object should be independent from the original one and functionally equivalent 3. Allocate the new object and make copies of all the instance variables. You might propagate the copy to the instance variables. 4. The new object is passed to the caller (who owns it)

11 Deep Copy (cont.) NSObject does not adopt NSCopying protocol itself [NSObject copy] translates to a convenience method that sends a copywithzone:nil message If copywithzone: is not implemented in the inheritance chain an exception is thrown A copy of an array results in a shallow copy (the array object itself does not implement the NSCopying protocol) To deep-copy an array Initialize a new array with copies of the original array's objects The objects in the new array are independent and functionally equivalent to the objects in the original array You own the new objects

12 Deep Copy (cont.) int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; Person *a = [[Person alloc] init]; NSArray *arr1 = [NSArray arraywithobjects:a, b, c, d, nil]; NSArray *arr2 = [NSArray arraywithobjects: [[a copy] autorelease] // Autorelease adds to [[b copy] autorelease] // the pool (RC = 2) nil]; ; [pool release]; [a release]; [d release]; return 0;

13 Deep Copy (cont.)

14 Sorting an Array Two methods Write a function that finds the proper order of two objects Write a method to your class that allows an instance to compare itself to another instance of the same class The comparator function should return one of the following (NSInteger) NSOrderedAscending: a < b NSOrderedSame: a == b NSOrderedDescending: a > b

15 Sorting an Array Person : NSObject { NSString *name; NSInteger (copy) NSString NSString NSInteger intsort (id a, id b, void *context) { int val1 = [(Person *)a id]; int val2 = [(Person *)b id]; if (val1 < val2) return NSOrderedAscending; else if (val1 == val2) return NSOrderedSame; else return NSOrderedDescending; int main( { Person *a = [[Person alloc] init]; NSArray *arr1 = [NSArray initwithobjects: a, b, c,, nil]; NSArray *arr2 = [arr1 sortedarrayusingfunction:intsort context: NULL];

16 Sorting an Array Person : NSObject { NSString *name; NSInteger (copy) NSString NSString id; -(NSComparisonResult) namecompare:(person *aperson); // Person -(NSComparisonResult) namecompare:(person *)aperson { return [name caseinsensitivecompare:[aperson

17 Sorting Arrays (cont.) int main( { Person *a = [[Person alloc] init]; NSArray *arr1 = [NSArray initwithobjects: a, b, c,, nil]; NSArray *arr2 = [arr1 sortedarrayusingselector:@selector(namecompare:)];

18 Sets Unique objects and fast verification mechanism of object membership No support for sorting (use NSArray/NSMutableArray) Mutable and immutable versions (NSSet/NSMutableSet) Immutable sets methods initwithobjects: a, b,, nil - (BOOL) intersectswithset: (NSSet *)otherset - (BOOL) issubsetofset:(nsset *)otherset - (BOOL) isequaltoset:(nsset *) otherset - (BOOL) containsobject:(id)anobject

19 Mutable Sets Mutable sets methods [[NSMutableSet alloc] initwithcapacity: 2] - (void) unionset:(nsset *)otherset - (void) minusset:(nsset *)otherset - (void) addobject:(id)anobject - (void) removeobject:(id)anobject Other Methods (NSSet) - (void) removeallobjects - (void) setset:(nsset *)replacementset - (void) addobjectsfromarray:(nsarray *)anarray Send a Message to all objects - (void) makeobjectsperformselector:(sel)aselector - (void) makeobjectsperformselector:(sel)aselector withobject:(id)anobject

20 Dictionaries Allow to store key/values pair Any object can be used as a Key must implement NSCopying protocol usually instances of NSString are used as keys Keys have to be unique Values can not be nil Use NSNull class to store empty objects When an object is added to a dictionary A copy of the key is made The value object is retained

21 Dictionaries (cont.) Using Enumerators to traverse a dictionary NSMutableArray karr = nil]; NSMutableArray aarr = [NSMutableArray arraywithobjects:@"2", nil]; NSDictionary *dir = [NSDictionary dictionarywithobjectsandkeys: nil]; NSEnumerator *enum = [dir keyenumerator]; id key; while((key = [enum nextobject])) { if([[key substringtoindex:1] isequal:@"s"]) { [[dir objectforkey:key] addobject:@"5"];

22 Dictionaries (cont.) Using allkeys to traverse a Dictionary NSMutableArray karr = nil]; NSMutableArray aarr = [NSMutableArray arraywithobjects:@"2", nil]; NSDictionary *dir = [NSDictionary dictionarywithobjectsandkeys: nil]; for (id keyindictionary in [dir allkeys]) { id objectforkey = [dir objectforkey:keyindictionary] NSLog(@"Key = %@, Object = %@", keyindictionary, objectforkey);

23 Dictionaries (cont.) Using 'in' to traverse a dictionary NSMutableArray karr = nil]; NSMutableArray aarr = [NSMutableArray arraywithobjects:@"2", nil]; NSDictionary *dir = [NSDictionary dictionarywithobjectsandkeys: nil]; NSMutableDictionary *dyndir = [dir mutablecopy]; id key; for(key in dyndir) { if([[key substringtoindex:1] isequal:@"m"]) { [[dyndir objectforkey:key] addobject:@"5"];

24 Dictionaries (cont.) Using an NSArray to traverse a dictionary NSMutableArray karr = nil]; NSMutableArray aarr = [NSMutableArray arraywithobjects:@"2", nil]; NSDictionary *dir = [NSDictionary dictionarywithobjectsandkeys: nil]; NSMutableDictionary *dyndir = [dir mutablecopy]; NSArray *keys = [dyndir allkeys]; id key; for(key in keys) { if([[key substringtoindex:1] isequal:@"s"]) { [dyndir removeobjectforkey:key];