universal array in objective C

Question

I am making my first app, and already made it on android, and am now trying to make it on iphone, but have no objective c experience. The app is super simple except for one part, the array.

The app has a button, that when pressed, needs to store info into an array. The problem I am running into is that when I create the array in the method where the button-click actions take place, every time I click the button it creates a new array, defeating the point of the array. When I make the array outside of the method, it either doesn't pass into the method (error says undefined) or, when I declare the object in the .h file, the program compiles, but when I hit the button it crashes.

Any help would be greatly appreciated. Examples would be great, but even if someone could point me in the right direction of things to look up, that would save me from going bald.

I think you are looking for NSMutableArray, but I'm not sure since I didn't understand very well your question. Can you please clarify what you are trying to do and post the code that shows what you did? — Manlio
– Manlio, Commented Apr 11, 2012 at 17:07
What languages DO you know? Passing values is pretty much the same as in C/C++. It's just that the objects are funny-shaped and the calls look like array index ops. — Hot Licks
– Hot Licks, Commented Apr 11, 2012 at 17:24

SomaMan · Accepted Answer · 2012-04-11 17:18:56Z

3

Try something like this (this isn't ARC) -

@interface MyViewController : UIViewController {

    NSMutableArray *myArray;

}


@implementation MyViewController

-(id)init {

    self = [super init];

    if (self) {

        myArray = [[NSMutableArray alloc] init];

    }

    return self;

}


-(void)dealloc {

    [myArray release];

    [super dealloc];

}


-(IBAction)buttonPressed {

    [myArray addObject:someObject];

}

@end

answered Apr 11, 2012 at 17:18

SomaMan

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Comments

Sergey Kalinichenko · Accepted Answer · 2012-04-11 17:19:32Z

2

You need to declare your array as an instance variable (AKA "ivar") inside the curly braces section of the the interface declaration in your .h file, and also initialize it in your designated initializer.

In the .h file:

@interface MyClass : NSObject {
    NSMutableArray *myArray
}
// methods
@end

In the .m file:

-(id)init {
    self = [super init];
    if (self) {
        myArray = [NSMutableArray array];
    }
    return self;
}

Now you can use myArray in all instance methods of your class.

EDIT: This sample assumes that you are using automated reference counting. Since this is your first app, using ARC is a good idea (XCode asks you if you would like to use it when you create a new project).

edited Apr 11, 2012 at 17:19

answered Apr 11, 2012 at 17:12

Sergey Kalinichenko

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3 Comments

Joe Over a year ago

You should specify that this example is ARC. The OP may not be using ARC since the application crashed when using the array declared in the header (assuming it was properly defined in the interface).

Sergey Kalinichenko Over a year ago

@Joe You are right, I sort of assumed that it's ARC because of the "I am making my first app" part of the post, but there is no 100% certainty. Thanks!

SomaMan Over a year ago

@dasblinkenlight sorry just duplicated your answer sort of, it wasn't here when I started writing it!

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