addObject for NSMutableArray not working - ios

Question

#property (strong, nonatomic)NSMutableArray *billsArray;
- (void)viewDidLoad {
[super viewDidLoad];
self.billsUserDefault = [NSUserDefaults standardUserDefaults];
self.billsArray = [[NSMutableArray alloc] init];
self.billsArray = [self getBillsArray];
}
- (NSMutableArray *)getBillsArray {
NSMutableArray *billsArr = [self.billsUserDefault objectForKey:#"billArray"];
return billsArr;
}
- (void)AddOneBill:(Bill *)bill {
// add bill to array
[self.billsArray addObject:bill];
// store the new bill
[self.billsUserDefault setObject:self.billsArray forKey:#"billArray"];
[self.billsUserDefault synchronize];
// reload the table view
[self.billTableView reloadData];
}
The addObject method in addOneBill: method does not work.
I have googled the same problem， others also met this problem. The answers suggested to add [[NSMutableArray alloc] init] for mutable array. I did but not works.

Answer 1

In your getBillsArray method, add mutableCopy call to get mutable array for objectForKey. Because objects got from NSUserDefaults are not mutable. Modified code would look like this:
- (NSMutableArray *)getBillsArray {
NSMutableArray *billsArr = [[self.billsUserDefault objectForKey:#"billArray"] mutableCopy];
return billsArr;
}
EDIT:
You are adding custom objects in array and trying to save in NSUserDefaults which is not possible. You need to convert your object into NSDictionary object in which each key value pair will represent one variable of that object. You will have to recursively do this conversion step if your custom object also contain custom objects.

Answer 2

- (void)viewDidLoad {
[super viewDidLoad];
self.billsUserDefault = [NSUserDefaults standardUserDefaults];
self.billsArray = [[NSMutableArray alloc] init];
self.billsArray = [self getBillsArray];
}
In viewDidLoad you call getBillsArray. But what value in userDefauls for key - billArray you what to get at viewController start?
You set array for this key in addOneBill method.
So in viewDidLoad you creates mutableArray:
self.billsArray = [[NSMutableArray alloc] init];
and then set it to nil here:
self.billsArray = [self getBillsArray];

Answer 3

Try
NSMutableArray *billsArr = [[self.billsUserDefault objectForKey:#"billArray"] mutableCopy]; in getBillsArray

Answer 4

NSUserDefaults objects are not not mutable. You have to make them mutable.
try following code.
NSMutableArray *billsArr = [NSMutableArray arrayWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:#"billArray"]];

Answer 5

Another solution : For the explication why it does not work, see Salman's answer (Returned values from NSUserDefaults are not mutable)
- (void)viewDidLoad {
[super viewDidLoad];
self.billsUserDefault = [NSUserDefaults standardUserDefaults];
self.billsArray = [[NSMutableArray alloc] init];
[self.billsArray addObjectsFromArray: [self getBillsArray]];
}
- (NSArray *)getBillsArray {
NSArray *billsArr = [self.billsUserDefault objectForKey:#"billArray"];
return billsArr;
}
In order to save your 'Bill' objects into NSUserDefaults, if it's derived from NSObject, you can use NSKeyedArchiver & NSKeyedUnarchvier:
//encode
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:your_bill_array];
//then save to NSUserDefaults
//decode:
id result = [NSKeyedUnarchiver unarchiveObjectWithData:data_returned_from_NSUSerDefaults];