Question

I’m trying to access a NSMutableArray from a different already existing class than it was created in. But if i NSLog it, i get null. My program starts up in class2, then I segue to class1, create my NSMutableArray by pressing one or more rows, and then I want my class2 to get the updated NSMutableArray instance, but all it get is null. Code below:

//class1.m

#import "FocusTagTableViewController.h"
#import "STATableViewController.h"

@implementation FocusTagTableViewController

@synthesize focusArray = _focusArray;
@synthesize allSelectedFocus = _allSelectedFocus;

- (void)viewDidLoad
{
_focusArray = [[NSArray alloc]initWithObjects:@"Balance",@"Bevægelse",@"Elementskift",@"Vejrtrækning",@"Alle",nil];

[super viewDidLoad];

}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
NSString *selectedFocus = [[_focusArray objectAtIndex:indexPath.row] stringByAppendingString:@","];
if(_allSelectedFocus == nil)
{
    _allSelectedFocus = [[NSMutableArray alloc]init];
    [_allSelectedFocus addObject:selectedFocus]; 
}
else if(![_allSelectedFocus containsObject:selectedFocus])
{
    [_allSelectedFocus addObject:selectedFocus];
}
}

//class2.m

#import "STATableViewController.h"
#import "FocusTagTableViewController.h"

@implementation STATableViewController
- (void)viewDidLoad
{
[super viewDidLoad];

 FocusTagTableViewController *focusTag = [[FocusTagTableViewController alloc]init];

[focustag addObserver:self forKeyPath:@"allSelectedFocus" options:NSKeyValueObservingOptionNew context:NULL];
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if([keyPath isEqualToString:@"allSelectedFocus"])
{
    NSLog(@"%@", [object valueForKeyPath:keyPath]);
}
}

Answer 1

That’s because in class 2 you create a new instance of class 1, wich has empty array.
If you want to access that array from class 2, you should make a reference to that first class. Or you could use Key-Value-Observing for that.

Here is the docs about KVO
http://developer.apple.com/library/mac/ipad/#documentation/Cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html

In first class, when you create class two, add self as an observer for that array, and implement observeValueForKeyPath: method in class 1