How to initialize an empty mutable array in Objective C

Question

I have a list of objects (trucks) with various attributes that populate a tableview. When you tap them they go to an individual truck page. There is an add button which will add them to the favorite list in another tableview. How do I initialize an empty mutable array in Cocoa?

I have the following code:

-(IBAction)addTruckToFavorites:(id)sender:(FavoritesViewController *)controller
{
    [controller.listOfTrucks addObject: ((Truck_Tracker_AppAppDelegate *)[UIApplication sharedApplication].delegate).selectedTruck];

}

You shouldn't make the controller's mutable array public like that. The controller should only make an immutable array available to other objects; for adding a new truck, you should add a method to the controller that does that. Then, instead of getting the `listOfTrucks` and directly changing it without the controller's knowledge, you tell the controller to make the change. — Peter Hosey, Apr 20 '12 at 20:42

score 44 · Accepted Answer · edited May 23 '17 at 10:31

44

Update:

With new syntax you can use:

NSMutableArray *myArray = [NSMutableArray new];

Original answer:

for example:

NSMutableArray *myArray = [[NSMutableArray alloc] init];

And here you find out why (difference between class and instance method)

edited May 23 '17 at 10:31

Community

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answered Apr 19 '12 at 10:06

Jakub

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Even if the array is initially empty, if you know that you will be putting a certain number of objects into it, `initWithCapacity:` may make that population step faster (because the array may initially create its backing storage with space for that many objects). – Peter Hosey Apr 20 '12 at 20:37
Moreover, autorelease is not the evil that some people make it out to be. There's nothing wrong with `[NSMutableArray array]`; it's just not appropriate for this case, assuming that the controller will assign the new array directly to its private `_listOfTrucks` instance variable. – Peter Hosey Apr 20 '12 at 20:38

score 11 · Answer 2 · edited Jul 20 '16 at 23:54

11

Basically, there are three options:

First

NSMutableArray *myMutableArray = [[NSMutableArray alloc] init];

Second

NSMutableArray *myMutableArray = [NSMutableArray new];

Third

NSMutableArray *myMutableArray = [NSMutableArray array];

edited Jul 20 '16 at 23:54

Jianxin Gao

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answered Mar 06 '16 at 16:35

Sangram Shivankar

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score 4 · Answer 3 · answered Oct 05 '16 at 09:27

4

You can also initialize in this way

Another way for Objective C apart from the answer of @NSSam

NSMutableArray *myMutableArray = [@[] mutableCopy];

For Swift

let myArray = NSMutableArray()

OR

let myArray = [].mutableCopy() as! NSMutableArray;

answered Oct 05 '16 at 09:27

Janmenjaya

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score 2 · Answer 4 · answered Apr 19 '12 at 08:57

2

NSMutableArray *arr = [NSMutableArray array];

answered Apr 19 '12 at 08:57

fbernardo

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score 2 · Answer 5 · answered Jul 01 '18 at 11:01

2

I use this way to initialize an empty mutable array in Objective C:

NSMutableArray * array = [NSMutableArray arrayWithCapacity:0];

answered Jul 01 '18 at 11:01

Agisight

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score 0 · Answer 6 · answered Apr 19 '12 at 08:57

0

listOfTrucks = [NSMutableArray array]; gives you a new mutable array.

answered Apr 19 '12 at 08:57

jtbandes

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GeRyCh · Answer 7 · 2018-08-07T12:21:39.537

-1

In modern Objective - C it could be even more shorter:

NSArray *array = @[];

edited Aug 07 '18 at 12:21

answered Jul 02 '18 at 09:22

GeRyCh

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This doesn't create a *mutable* array. – saagarjha Aug 12 '18 at 00:01

How to initialize an empty mutable array in Objective C

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