How to add objects into NSMutableArray without deleting the existing ones?

Question

Im having trouble with my nsmutablearray in NSUserdefaults, this array every time I relaunch the app erases the objects that already are there and put the new ones, so I need help to prevent these to happen, Thanks and this is my code;

NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];

    if (!self.tasks) self.tasks = [NSMutableArray new];

    [self.tasks addObject:textField.text];
    [userDefaults setObject:self.tasks forKey:@"tasks"];
    //[userDefaults synchronize];
    NSLog(@"tasks:%@", [[NSUserDefaults standardUserDefaults]objectForKey:@"tasks"]);
    NSLog(@"number of tasks:%d", self.tasks.count);

And Im reading it in a tableview this way:

cell.taskTitle.text = (self.TasksArray)[indexPath.row];

Thanks!

Answer 1

You are missing a line of code there:

self.tasks = [[NSMutableArray alloc] initWithArray:[userDefaults objectForKey:@"tasks"];

As far as I can tell, you're not initially setting your ".tasks" property, so adding that bit may fix the problem.

Answer 2

You need to get it from user defaults first as rmaddy suggests. Your nil check will then create a new array if its never been created/saved before.

NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];

self.tasks = [[userDefaults objectForKey:@"tasks"] mutableCopy];

if (!self.tasks) self.tasks = [NSMutableArray new];

[self.tasks addObject:textField.text];
[userDefaults setObject:self.tasks forKey:@"tasks"];
//[userDefaults synchronize];
NSLog(@"tasks:%@", [[NSUserDefaults standardUserDefaults]objectForKey:@"tasks"]);
NSLog(@"number of tasks:%d", self.tasks.count);

Answer 3

I see you never call [[NSUserDefaults standardUserDefaults] synchronize]; Once you finish with changes of your object you should call it since it saves your changes to disk.