How to keep objects in NSMutableArray? - ios

Question

There are two view controllers.One to add items,the other one to display(table view).All items are stored in an NSMutableArray.But every time I unwind to add item and when I go back to the table view, there is only the newest item left.
Code:
- (void)viewDidLoad {
[super viewDidLoad];
[self addData];
}
- (void)addData {
if (!self.items) {
self.items = [[NSMutableArray alloc] init];
}
[self.items addObject:self.textFromFirst];
}
// textFormFirst is an NSString which received from the previous view controller
add view controller
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
UINavigationController *nav = [segue destinationViewController];
SecondController *second = [nav.viewControllers objectAtIndex:0];
second.textFromFirst = [self getText]; // get inputed string
self.aTextField.text = #"";
}

Answer 1

You can share an NSMutableArray between your two view controllers. Just use a property:
MainViewController:
// .m
#interface MasterViewController ()
#property (nonatomic, strong) NSMutableArray *items;
#end
#implementation MasterViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.items = [NSMutableArray array];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"ShowDetail"]) {
DetailViewController *controller = (DetailViewController *)[segue destinationViewController];
controller.items = self.items;
controller.textFromFirst = #"This is a test";
}
}
#end
AddViewController:
// .h
#interface DetailViewController : UIViewController
#property (nonatomic, copy) NSString *textFromFirst;
#property (nonatomic, strong) NSMutableArray *items;
#end
// .m
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self addData];
}
- (void)addData {
[self.items addObject:self.textFromFirst];
}
These is a sample project: https://www.dropbox.com/s/ymum4zivgi0z688/TestUnwindSegue.zip?dl=0
I do not know why are you using array in AddViewController. Maybe you are prefer use unwind segue, like so:
// MainViewController.m
- (IBAction)saveItem:(UIStoryboardSegue *)segue {
DetailViewController *detailVC = segue.sourceViewController;
[self.items addObject:detailVC.textFromFirst];
}
In the case, you don't need to share an NSMutableArray to AddViewController.

Answer 2

How are you persisting the NSMutableArray between view controllers? If you need to persist one array across your entire application I would suggest you use a singleton. A singleton is an object that each instance has only 1 memory address, thus is always the same object. You could accomplish this by doing the following:
1) Press CMD+N and select "Cocoa Touch Class" / subclass NSMutableArray
2) Go to that class' .m file and add the singleton in init
static YourNSMutableArray *highlander;
#implementation YourNSMutableArray
- (instancetype)init {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
highlander = [super init];
});
return highlander;
}
3) Now whenever you create a new instance in any of your view controllers like this
if (!self.items) {
self.items = [YourNSMutableArray new];
}
[self.items addObject:self.textFromFirst];
self.items will always have the stored self.textFromFirst because any YourNSMutableArray you create in your app will always be the same object.