Question

Given a basic key/value array, I’m wanting to store two sorted arrays based on the original array: one array will be sorted by name, and the other by age.

The arrays seem to be sorting correctly when I output them to the log; however, when I try to access them elsewhere in the code, I’m receiving a EXC_BAD_ACCESS error.

Here’s what I have so far:

// MyController.h

@interface MyController : UIViewController {
    NSMutableArray *originalArray;
    NSMutableArray *nameArray;
    NSMutableArray *ageArray;   
}

@property (nonatomic, retain) NSMutableArray *originalArray;
@property (nonatomic, retain) NSMutableArray *nameArray;
@property (nonatomic, retain) NSMutableArray *ageArray;

-(void)someRandomMethod;

@end


// MyController.m

#import "MyController.h"

@implementation MyController

@synthesize originalArray;
@synthesize nameArray;
@synthesize ageArray;

-(void)viewDidLoad {

    // originalArray = (
    //   {
    //     "name" = "Sally";
    //     "age" = 18;
    //   },
    //   {
    //     "name" = "Chad";
    //     "age" = 26;
    //   },
    //   {
    //     "name" = "Carla";
    //     "age" = 24;
    //   },
    // )

    // sort by name
    NSSortDescriptor *sortByNameDescriptor;
    sortByNameDescriptor = [[[NSSortDescriptor alloc]              
                                    initWithKey:@"name"                                                             
                                    ascending:NO] autorelease];
    NSArray *sortByNameDescriptors = [NSArray arrayWithObject:sortByNameDescriptor];
    nameArray = [originalArray sortedArrayUsingDescriptors:sortByNameDescriptors];  

    // sort by age
    NSSortDescriptor *sortByAgeDescriptor;
    sortByAgeDescriptor = [[[NSSortDescriptor alloc]              
                                    initWithKey:@"age"                                                              
                                    ascending:NO] autorelease];
    NSArray *sortAgeDescriptors = [NSArray arrayWithObject:sortByAgeDescriptor];
    ageArray = [originalArray sortedArrayUsingDescriptors:sortByAgeDescriptors];    

    [super viewDidLoad];
}

-(void)someRandomMethod {
    // whenever I try to access the sorted arrays, I receive the EXC_BAD_ACCESS error
    [[nameArray objectAtIndex:0] valueForKey:@"name"];
    [[ageArray objectAtIndex:0] valueForKey:@"age"];
}

-(void)viewDidUnload {
    self.originalArray = nil;
    self.nameArray = nil;
    self.ageArray = nil;
    [super viewDidUnload];
}

- (void)dealloc {
    [originalArray release];
    [nameArray release];
    [ageArray release];
    [super dealloc];
}

@end

Any ideas?

UPDATE: Thanks to @robin, by changing the code above to the code below, everything works great:

// sort by name
NSSortDescriptor *sortByNameDescriptor;
sortByNameDescriptor = [[[NSSortDescriptor alloc]              
                                initWithKey:@"name"                                                             
                                ascending:NO] autorelease];
NSArray *sortByNameDescriptors = [NSArray arrayWithObject:sortByNameDescriptor];
nameArray = [[NSMutableArray alloc] initWithArray:[originalArray sortedArrayUsingDescriptors:sortByNameDescriptors]];  

// sort by age
NSSortDescriptor *sortByAgeDescriptor;
sortByAgeDescriptor = [[[NSSortDescriptor alloc]              
                                initWithKey:@"age"                                                              
                                ascending:NO] autorelease];
NSArray *sortAgeDescriptors = [NSArray arrayWithObject:sortByAgeDescriptor];
ageArray = [[NSMutableArray alloc] initWithArray:[originalArray sortedArrayUsingDescriptors:sortByAgeDescriptors]];    

Answer 1

I dont think you know about this or not but when ever you create an object like string or array or dictionary, with init methods then the retain count gets incremented by 1

and if you create them like this

NSArray *anarray = [NSArray arrayWithArray:temp];

this will create an autorelease objects that will be released automatically after sometime.

So my advice don’t use this type of code if you want to use the objects in more than 1 function. Always use init methods first to get the work done.

and if you are sure that the objects are not needed for the rest of the program than release them using release methode.