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
– Peter Hosey, Commented Apr 20, 2012 at 20:42

Community · Accepted Answer · 2017-05-23 10:31:02Z

46

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, 2017 at 10:31

CommunityBot

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answered Apr 19, 2012 at 10:06

Jakub

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2 Comments

Peter Hosey Over a year ago

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 Over a year ago

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.

Jianxin Gao · Accepted Answer · 2016-07-20 23:54:00Z

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, 2016 at 23:54

Jianxin Gao

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answered Mar 6, 2016 at 16:35

Sangram Shivankar

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Comments

Janmenjaya · Accepted Answer · 2016-10-05 09:27:40Z

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 5, 2016 at 9:27

Janmenjaya

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Comments

fbernardo · Accepted Answer · 2012-04-19 08:57:28Z

2

NSMutableArray *arr = [NSMutableArray array];

answered Apr 19, 2012 at 8:57

fbernardo

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Comments

Agisight · Accepted Answer · 2018-07-01 11:01:36Z

2

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

NSMutableArray * array = [NSMutableArray arrayWithCapacity:0];

answered Jul 1, 2018 at 11:01

Agisight

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Comments

jtbandes · Accepted Answer · 2012-04-19 08:57:39Z

0

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

answered Apr 19, 2012 at 8:57

jtbandes

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Comments

GeRyCh · Accepted Answer · 2018-08-07 12:21:39Z

0

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

NSArray *array = @[];

edited Aug 7, 2018 at 12:21

answered Jul 2, 2018 at 9:22

GeRyCh

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1 Comment

saagarjha Over a year ago

This doesn't create a mutable array.

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