NSUserDefaults doesn't work

Question

I am new in programming and i have one problem. I create app, with two views. First is tableviewcontroller and second is view controller. from second view i sending data into my tableview trough perepareForSegue method. My data (Strings) are NSMutableArray and this MutableArray i want to save into UsedDefault after my app didEnterBackgoung in appDelegate.m Then i want to load it back, but nothing happened. I put my code in appDidBecomeActive in appDelegate.m and i already try write it in my first view viewDidLoad, but no action. My MuttableArray is still empty, after new app start.

here is my code:

- (void)applicationDidEnterBackground:(UIApplication *)application
{
NSUserDefaults*defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:self.flipsideView.zoznamFunkcii forKey:@"NSMutableArray"];
[defaults synchronize];
}

flipsideView is my first View and zoznamFunkcii is my NSMuttable array

and this is my load method:

- (void)applicationDidBecomeActive:(UIApplication *)application
{
NSUserDefaults*defaults = [NSUserDefaults standardUserDefaults];
self.flipsideView.zoznamFunkcii = [NSMutableArray arrayWithArray:[defaults  objectForKey:@"NSMutableArray"]];
}

Can anyone help me with that? I don't know why it not work.

Answer 1

You are saving an empty NSMutableArray to NSUserDefaults. So of course the loaded array will be empty as well.

Here is your saving code with comments:

// overwrite zoznamFunkcii with empty array
self.flipsideView.zoznamFunkcii = [[NSMutableArray alloc]init];

NSUserDefaults*defaults = [NSUserDefaults standardUserDefaults];

// save this empty array to nsuserdefaults
[defaults setObject:self.flipsideView.zoznamFunkcii forKey:@"NSMutableArray"];

---

your saving code should probably look like this:

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    NSUserDefaults*defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:self.flipsideView.zoznamFunkcii forKey:@"NSMutableArray"];
}

and because NSUserDefault does not save mutable objects your restoration code should look like this:

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    NSUserDefaults*defaults = [NSUserDefaults standardUserDefaults];
    self.flipsideView.zoznamFunkcii = [NSMutableArray arrayWithArray:[defaults objectForKey:@"NSMutableArray"]];
}

---

and if the objects inside your array are not instances of NSData , NSString , NSNumber , NSDate , NSArray , or NSDictionary you have to encode your array first. See this question for details on how to do that.

Answer 2

Here you can Save Object With NSUserDefault..

[[NSUserDefaults standardUserDefaults]setObject:[NSKeyedArchiver archivedDataWithRootObject:self.flipsideView.zoznamFunkcii] forKey:@"NSMutableArray"];
    [[NSUserDefaults standardUserDefaults]synchronize];

and you make coder and decoder method

- (id)initWithCoder:(NSCoder *)decoder {
    if (self = [super init]) {
        self.toolResult = [decoder decodeObjectForKey:@"obj1"];
        self.toolNotes = [decoder decodeObjectForKey:@"obj2"];

     }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)encoder {
    [encoder encodeObject:self.toolResult forKey:@"obj1"];
    [encoder encodeObject:self.toolNotes forKey:@"obj2"];

}

your Data Save Into NsuserDefault When you Get Data From NsUserDefault then you Use like
[NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:@"NSMutableArray"]];