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iOS Build a Simple iPhone App with Objective-C Creating a Data Model Creating a Data Collection

carlos carrillo
carlos carrillo
1,197 Points
Posted by carlos carrillo
carlos carrillo
1,197 Points

not sure how I'm meant to retrieve the string eggs from the shoppingList array and store it in shoppingCart.. :(

this is what I've typed in.

self.shoppingCart = [ShoppingList objectAtIndex:2];

ViewController.h 
#import "UIViewController.h"

@interface ViewController : UIViewController

@property (strong, nonatomic) NSString *shoppingCart;

@property (strong, nonatomic) NSArray *shoppingList;

@end
ViewController.m 
#import "ViewController.h"

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.shoppingList = [[NSArray alloc] initWithObjects:@"toothpaste", @"bread", @"eggs", nil];

    self.shoppingCart = [shoppingList objectAtIndex:2];


}

@end

7 Answers

Marius Kildedal
Marius Kildedal
8,096 Points
Marius Kildedal
Marius Kildedal
8,096 Points

Try putting the self.shoppingCart inside the [ ]

Stephen Whitfield
Stephen Whitfield
16,771 Points
Stephen Whitfield
Stephen Whitfield
16,771 Points

You have to access the index of the array that corresponds to that element.

arrayName[index]

ajor
ajor
8,216 Points
ajor
ajor
8,216 Points

I am afraid I need a little bit more help. Why do we have to access the index of the array via arrayName[index]? Isn't [arrayName objectAtIndex:index] doing exactly that?

Stephen Whitfield
Stephen Whitfield
16,771 Points

Yes, they're the same. One is just a shorthand version of the other called a Literal.

ajor
ajor
8,216 Points
ajor
ajor
8,216 Points

Thank you for your quick reply, Stephen.

I have to admit now I am profoundly confused. Why is the following code not working hten?

  • (void)viewDidLoad { [super viewDidLoad];

    // Add your code below! self.shoppingList = [[NSArray alloc] initWithObjects:@"toothpaste", @"bread", @"eggs", nil];

    shoppingCart = [shoppingList objectAtIndex:2]; }

Stephen Whitfield
Stephen Whitfield
16,771 Points
Stephen Whitfield
Stephen Whitfield
16,771 Points

Because you aren't setting your properties correctly. If you have a property called shoppingCart and a property called shoppingList, if you want to access those properties, you have to either prepend "self." (or an underscore, but we'll use self. here). 

self.shoppingList = @[@"toothpaste", @"bread", @"eggs"];
self.shoppingCart = shoppingList[2];
ajor
ajor
8,216 Points
ajor
ajor
8,216 Points

Ok, that makes sense. However, this still returns the following error:

Bummer! Remember array indexes start at zero. Access the third item in the array and assign it to a string named shoppingCart.

Thank you so much for your help. It is much appreciated!

Stephen Whitfield
Stephen Whitfield
16,771 Points

The third item in the array "shoppingList" is the item at index 2. No idea why it's throwing that error. Good luck!

ajor
ajor
8,216 Points
ajor
ajor
8,216 Points

Yes, that's why I am so confused. Well, thank you so much for taking time to answer my questions. I learned quite a bit,