Question

i`m trying to make an NSMutableArray From NSUserDefaults so i can add/delete and edit it later

my code is

- (void)viewDidLoad {
[super viewDidLoad];

NSUserDefaults *ArrayTable = [NSUserDefaults standardUserDefaults];
[ArrayTable setObject:@"One" forKey:@"myArray"];
[ArrayTable setObject:@"Two" forKey:@"myArray"];
[ArrayTable setObject:@"Three" forKey:@"myArray"];
[ArrayTable setObject:@"Four" forKey:@"myArray"];
[ArrayTable setObject:@"Five" forKey:@"myArray"];
[ArrayTable synchronize];

NSMutableArray *array = [[NSMutableArray alloc] init];
array = [ArrayTable objectForKey:@"myArray"];
}


- (void)viewDidUnload
{
    [super viewDidUnload];
}

#pragma mark - Table View

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [array count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    }
    cell.textLabel.text = [array objectAtIndex:indexPath.row];
    return cell;
}

when i build and run nothing shows up

i googled it but with no help, i`m sure i didn’t understand how to do it

what i need is to build an app that contain a tableview with empty data, the use will fill in the data Add/Delete/Edit

can someone please explain it for me

thank you in advance

Answer 1

First, you assigned your array from the user defaults to a local variable named array. Assuming you have a property for this class also named array, this local assignment masks that. If it had not, you would have crashed when you tried to call -count on a string.

The NSUserDefaults object is a dictionary. Each time you call -setObject:forKey: on it, you are actually replacing the object previously set for that key. So at the end of your series of calls to -setObject:forKey:, the resulting value is the NSString Five.

You can’t really store a mutable object in the NSUserDefaults, instead you would take a mutable copy of the object when you assign it to your local variable or ivar. To get the behavior you are probably expecting, you should do something like the following:

- (void)viewDidLoad
{
  // Create the array template and store it in NSUserDefaults
  NSArray* arrayTemplate = [NSArray arrayWithObjects:@"One", @"Two", @"Three", @"Four", @"Five", nil];
  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
  [defaults setObject:arrayTemplate forKey:@"myArray"];
  [defaults synchronize];

  // Retrieve a mutable copy of the array from user defaults and assign it to the
  // the property 'array' <- note, this should be an NSMutableArray
  self.array = [[defaults objectForKey:@"myArray"] mutableCopy]; // if not using arc, autorelease this here
}

With that example code, it should behave the way you expected it to behave, and you can continue on. Obviously it makes no sense to set the array in -viewDidLoad and then immediately read a mutable copy. The key thing to keep in mind is that -setObject:forKey: will always replace any object already set for that key. It doesn’t add elements or anything like that.