Sort NSArray of custom objects by inherited property when adding new object

Question

Class "Person" is inherited by "Employee" which is inherited by "EmployeeList"

In my main model I initialize a new Employee object, setting the firstName and lastName, and then addEmployee to an EmployeeList.

Inside the addEmployee method I want to sort the NSArray of Employee objects by lastName

Here is what I've tried but it's not sorting the list.

#import "EmployeeList.h"

@interface EmployeeList()
@property (strong, nonatomic) NSMutableArray *employees;  // of Employee
@end


@implementation EmployeeList

- (NSMutableArray *)employees
{
    if (!_employees) _employees = [[NSMutableArray alloc] init];
    return _employees;
}

- (void)addEmployee:(Employee *)employee
{
    [self.employees addObject:employee];

    NSSortDescriptor *sortDescriptor =
    [NSSortDescriptor sortDescriptorWithKey:@"lastName"
                                  ascending:YES
                                   selector:@selector(caseInsensitiveCompare:)];
    [self.employees sortedArrayUsingDescriptors:@[sortDescriptor]];

    _numberEmployees++;
}

Main model:

EmployeeList *mgrList = [[EmployeeList alloc] init];

Employee *employee = [[Employee alloc] init];
employee.firstName = object[@"firstName"];
employee.lastName  = object[@"lastName"];
employee.phoneNumber = object[@"phoneNumber"];

[mgrList addEmployee:employee];

So does Employee have a method called caseInsensitiveCompare:? I doubt (because that's an NSString method). Read the documentation of NSSortDescriptor and think about your code. — The Paramagnetic Croissant
– The Paramagnetic Croissant, Commented May 4, 2014 at 22:55
Actually, I've realized the crash was unrelated and solved the crash. — Automate This
– Automate This, Commented May 4, 2014 at 23:00

rmaddy · Accepted Answer · 2014-05-04 23:06:48Z

2

Change this:

[self.employees sortedArrayUsingDescriptors:@[sortDescriptor]];

to:

[self.employees sortUsingDescriptors:@[sortDescriptor]];

answered May 4, 2014 at 23:06

rmaddy

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2 Comments

Automate This Over a year ago

Thank you, that makes more sense now and solved my problem. I've spent a lot of time on this simple problem as I'm pretty new to Obj-C.

rmaddy Over a year ago

sortedArrayUsingDescriptors: doesn't sort the original array, it returns a new sorted array.

Matteo Gobbi · Accepted Answer · 2014-05-04 23:06:30Z

1

Ok your code need a refactor:

#import "EmployeeList.h"

@interface EmployeeList()
@property (strong, nonatomic) NSMutableArray *employees;  // of Employee
@end


@implementation EmployeeList

//This is a more elegant solution to init
- (NSMutableArray *)employees
{
    dispatch_token_t token;
    dispatch_once(&token, ^{
        _employees = [NSMutableArray new];
    });
    return _employees;
}

- (void)addEmployee:(Employee *)employee
{
    [self.employees addObject:employee];

    NSSortDescriptor *sortDescriptor =
    [NSSortDescriptor sortDescriptorWithKey:@"lastName"
                                  ascending:YES
                                   selector:@selector(caseInsensitiveCompare:)];

    //This return an array so if you don't take it you don't have any change.
    NSArray *newArray = [[self.employees copy] sortedArrayUsingDescriptors:@[sortDescriptor]];

    //Then you can remove and add again all the object to the NSMutableArray
    [self.employees removeAllObjects];
    [self.employees addObjectsFromArray:newArray];

    //This is not needed because you can access to this information by
    //[self.employees count]
    //_numberEmployees++;
}

Be careful because you self.employees is mutable.

edited May 4, 2014 at 23:06

answered May 4, 2014 at 23:00

Matteo Gobbi

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5 Comments

Matteo Gobbi Over a year ago

i know that is inefficient, just took the code of the user. He says that the crash was unrelated and so i think that his problem was just that didn't save the array. EDIT: You deleted your comment and down vote, and you focus the problem by my response providing a little bit different answer..fox..np!

rmaddy Over a year ago

My original comment was based on the original question which was about a crash. After the question was updated to simply point out the actual problem, I posted my answer. I originally down voted because your answer had nothing to do with a crash. But please be aware that your solution is really not a good way to sort an existing mutable array. There is no reason to create an immutable copy of the array, create a new, sorted array, clear out the original mutable array, and then populate the empty mutable array with the sorted array. Just use one method to sort the mutable array in place.

Matteo Gobbi Over a year ago

Sure, you are right but not on every thing. Your code is better because sort the array locally, but is not safe. If i add something to the array while is ordering, the app crash. You need to use some synchronized scope or use immutable copy. In any case, i would have write my code totally in another way.

rmaddy Over a year ago

There was nothing in the question about needing to be thread-safe. That's a whole other level of complexity beyond this question.

Matteo Gobbi Over a year ago

There was nothing about performance as well..nay, i used the same code of the user. I know of the performance, and you should about the thread safe

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