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!

Initialize the array with the current values from `NSUserDefaults`, then add the new value, then save the updated list back to `NSUserDefaults`. — rmaddy, Mar 11 '14 at 22:45

Michael Dautermann · Accepted Answer · 2014-03-11T23:02:49.717

4

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.

edited Mar 11 '14 at 23:02

answered Mar 11 '14 at 22:46

Michael Dautermann

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self.tasks might be nil if "`[userDefaults objectForKey:@"tasks"]`" is nil. So we're protecting against that. – Michael Dautermann Mar 11 '14 at 22:50
Okay @mustafabesnili you win... I see Konrad's answer [in this related question](http://stackoverflow.com/a/12728920/981049). I've fixed my answer. – Michael Dautermann Mar 11 '14 at 23:03

score 0 · Answer 2 · answered Mar 11 '14 at 22:50

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);

score 0 · Answer 3 · answered Mar 11 '14 at 22:55

0

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.

answered Mar 11 '14 at 22:55

Josip B.

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You are correct but you still do not know when is that "periodically" moment. Calling synchronized can sometimes save your hair in the end :) – Josip B. Mar 11 '14 at 22:58

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

3 Answers3