iOS - Instance Array not holding data

Question

For some reason I can't get twitterAccounts to hold another arrays data.

ViewController.h

@interface ViewController : UIViewController <UITableViewDelegate, UITableViewDataSource>

@property (strong, nonatomic) NSArray *twitterAccounts;
@property (strong, nonatomic) IBOutlet UITableView *chooseTwitterAccountTableView;

- (void)twitterRequest;

@end

ViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    _twitterAccounts = [[NSArray alloc]init];

    [self twitterRequest];

}

- (void)twitterRequest {

    ACAccountStore *account = [[ACAccountStore alloc]init];
    ACAccountType *accountType = [account accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierTwitter];

    [account requestAccessToAccountsWithType:accountType options:nil completion:^(BOOL granted, NSError *error) {

        if (granted == YES) {

            NSArray *twitterAccountsTemp = [account accountsWithAccountType:accountType];

            _twitterAccounts = twitterAccountsTemp;

            NSLog(@"Array first has: %lu elements.", [_twitterAccounts count]);


        }

    }];

}

What I don't understand is if I have my viewDidLoad method like this:

- (void)viewDidLoad
{
    [super viewDidLoad];

    _twitterAccounts = [[NSArray alloc]init];

    [self twitterRequest];

    NSLog(@"After method called: %lu", [_twitterAccounts count]);

}

The output is:

After method called 0.
Array first has: 1 elements.

is it not supposed to be the other way around since I'm calling the method before outputting the amount of elements in the array?

You did notice that `requestAccessToAccountsWithType` is an *asynchronous* method? - Btw. is it `_accounts` or `_twitterAccounts`? Please copy/paste your real code. — Martin R, Dec 29 '13 at 21:32
You're assigning to `_accounts` but logging `_twitterAccounts`... so which one is it? — Alladinian, Dec 29 '13 at 21:33
@HotLicks because I want that empty array to hold the data that aoAccounts holds. — Nathaly, Dec 29 '13 at 22:07
An empty NSArray by definition doesn't hold any data (and can never hold any data). You have a basic misconception between a pointer an an object. — Hot Licks, Dec 29 '13 at 22:08
accounts is defined in the header file: `@property (strong, nonatomic) NSArray *accounts;` — Nathaly, Dec 29 '13 at 22:10
@HotLicks but if i create the empty NSArray and set it to another NSArray down in another method, shouldn't the empty NSArray hold the other NSArray's value? — Nathaly, Dec 29 '13 at 22:12
No, if you create an empty NSArray it will remain empty -- an NSArray is immutable. If you have a pointer to an NSArray and store a pointer to a different NSArray over the first one, then you can access that second NSArray's contents, but the first array is gone (sort of -- may have leaked). — Hot Licks, Dec 29 '13 at 22:13
@user3000730: Does your `NSLog(@"Array first has ...` display the correct number? — Martin R, Dec 29 '13 at 22:14
@MartinR updated code, i explained what happens when the program runs — Nathaly, Dec 29 '13 at 22:18
So you print the number of elements in the array before you set them into the array??? — Hot Licks, Dec 30 '13 at 01:06

score 1 · Accepted Answer · answered Dec 29 '13 at 22:19

1

requestAccessToAccountsWithType: is an asynchronous method, which means that it only initiates the request and returns. The completion block is called later, when the request has completed.

Therefore, after calling

[self twitterRequest];

the _twitterAccounts array has not yet been assigned to. When the request has finished and the completion block is called, _twitterAccounts = twitterAccountsTemp; is executed, and you can update the UI at that point, if necessary.

answered Dec 29 '13 at 22:19

Martin R

529,903
94
1,240
1,382

is there a solution to get twitterAccounts to hold the data of twitterAccountsTemp? – Nathaly Dec 29 '13 at 22:21
@user3000730: Set a breakpoint at `NSArray *twitterAccountsTemp = ...`. You will see that the completion is called some time *later*. That's how asynchronous methods work, there is no way around it. – Martin R Dec 29 '13 at 22:24
ok thanks, my goal was to take the number of elements in that array and create a table view. so i needed the twitterAccounts array to hold it.. – Nathaly Dec 29 '13 at 22:28
@user3000730: You can update the table view from within the completion block (but on the main thread, see e.g. http://stackoverflow.com/a/18387414/1187415 for a similar issue). – Martin R Dec 29 '13 at 22:32

iOS - Instance Array not holding data

1 Answers1