Question

I am working in Xcode 4.5.1 in Objective-C. I’m making a hearing test and want to store relevant data to each question in an array. I made a singleton MyManager. I use this to store data.

It is working fine for simple int/float values etc., but I’m stuck trying to use NSMutableArray. I’m new to Objective-C, so I’m assuming/hoping I’ve made some obvious mistake.

So, I want to fill mySNRArray with float values. I’ve come to understand that I can’t simply add floats, because it will only take objects. Thus, I use NSNumber.

Problem: When I try to read the data that I’ve supposedly added to the NSMutableArray, I get (null).

I will now provide the relevant code:

MyManager.h

@interface MyManager : NSObject
{

NSMutableArray *mySNRArray;

}

@property (readwrite) NSMutableArray *mySNRArray;

+ (id)sharedManager;

@end

MyManager.m

@implementation MyManager

@synthesize mySNRArray;

+ (id)sharedManager
{
static MyManager *sharedMyManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^
    {

            sharedMyManager = [[self alloc] init];

    });

return sharedMyManager;
}

- (id)init
{
if (self = [super init])
{

    NSMutableArray *mySNRArray = [[NSMutableArray alloc]init];

}

return self;
}

@end

TestViewController.m

//First, I try to add a value to mySNRArray.

MyManager *Manager = [MyManager sharedManager];

NSNumber *tempStorage1 = [[NSNumber alloc] initWithFloat:mySNR];

[Manager.mySNRArray insertObject:tempStorage1 atIndex:questionNumber];

//The NSLog below is showing the correct value.

NSLog(@"%@ : mySNR", tempStorage1);


...


for (n = 0; n < questionNumber; n++)
{

//Second, I try to acces the values I supposedly added to mySNRArray. 

MyManager *Manager = [MyManager sharedManager];

//This NSLog below is showing (null).

NSLog(@"Value at %i in SNRArray = %@", n, [Manager.mySNRArray objectAtIndex:n]);

}


...

I hope somebody can explain my error.

Answer 1

change

NSMutableArray *mySNRArray = [[NSMutableArray alloc]init];

to

self->_mySNRArray = [[NSMutableArray alloc]init];

in your init method you are creating a local mutable array, but not assigning it to your property