Question

I am trying to save an NSMutableArray on device , but everytime I reload the application the data is erased.

I tried to use NSUserDefaults but the problem persists

here is the code I am using

-(void) addingData{

    [data addObject:theBarcodeString]; //data is the NSMutableArray

    [mainTableView reloadData]; //this is a UITableView where the data from the NSMutableArray is populated
    [self endText];
    history=[NSUserDefaults standardUserDefaults];
    [history        setObject:data          forKey:@"history"  ];
}

and here is where I load the data

- (void)viewDidLoad
{
    ...
    if (data == nil) {
        data = [[NSMutableArray alloc] init]; //onload it always goes to his line

    else {

        data=[[NSUserDefaults standardUserDefaults] objectForKey:@"history"  ];
    }
    ...
}

what am I doing wrong ?

Answer 1

You shouldn’t be testing to see if data == nil. Instead, just do:

data = [[NSArray alloc] initWithArray:[[NSUserDefaults standardUserDefaults] 
    objectForKey:@"history"]];

Note that you will have to release that later.

If you want data to be a mutable array, you must use:

data = [[NSUserDefaults standardUserDefaults] mutableArrayValueForKey:@"history"];

If you try to performing mutating operations on data without using mutableArrayValueForKey, you will get a crash, because all objects returned from NSUserDefaults are immutable.