Getting Null array

Question

I have following code :

- (IBAction)goButton:(id)sender 
{

    if(buttonCount==0)
    {
        previousStateArray=setUpArray;
          NSLog(@"previous array count=%d",[previousStateArray count]);
        [setUpArray removeAllObjects];
        for(Node *n in nodeArray)
        {
            if(![temp isEqualToString:n.strName])
            {
                [setUpArray addObject:n.strName];

            }
            temp=n.strName;         
        }    
    }
}  

- (IBAction)backButton:(id)sender 
{

    [setUpArray removeAllObjects];
    setUpArray=previousStateArray;
     NSLog(@"previous array count=%d",[previousStateArray count]);
    buttonCount--;       
  }

Both setUpArray and previousStateArray are declared in the -viewDidLoad method.My view is loading only once.In first NSLog i am getting 1 as a output but in second NSLog i am getting

0 as a output while none of my array initialize again . so why this is happening???

which array count is 1 and u get zero? previous?

Saad
– Saad

2012-05-14 06:58:41 +00:00
Commented May 14, 2012 at 6:58 — Saad
– Saad, Commented May 14, 2012 at 6:58

giorashc · Accepted Answer · 2012-05-14 07:05:12Z

1

Your problem is with your array pointers.

In goButton :

previousStateArray=setUpArray;

Now previousStateArray points to the same array setUpArray is pointing to.

[setUpArray removeAllObjects];

This removes all objects and now both pointers point to an empty array.

In backButton:

setUpArray=previousStateArray;

They both point to the same empty array so this line is redundant. You should keep a temporary pointer if you want to swap the pointers.

answered May 14, 2012 at 7:05

giorashc

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Comments

Parag Bafna · Accepted Answer · 2012-05-14 09:09:39Z

In your code

`previousStateArray=setUpArray;`  //previousStateArray pointing to same memory location of setUpArray.

Use - (void)setArray:(NSArray *)otherArray method of NSMutableArray class.

[previousStateArray setArray: setUpArray];
[setUpArray setArray:previousStateArray];  

- (IBAction)goButton:(id)sender 
{

    if(buttonCount==0)
    {
        [previousStateArray setArray: setUpArray];
          NSLog(@"previous array count=%d",[previousStateArray count]);
        [setUpArray removeAllObjects];
        for(Node *n in nodeArray)
        {
            if(![temp isEqualToString:n.strName])
            {
                [setUpArray addObject:n.strName];

            }
            temp=n.strName;         
        }    
    }
}  

- (IBAction)backButton:(id)sender 
{

    [setUpArray removeAllObjects];
    [setUpArray setArray:previousStateArray];
     NSLog(@"previous array count=%d",[previousStateArray count]);
    buttonCount--;       
  }

Maulik · Accepted Answer · 2012-05-14 07:08:46Z

0

Initialize the array

setUpArray = [[NSMuatableArray alloc] init];

edited May 14, 2012 at 7:08

Maulik

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answered May 14, 2012 at 6:53

Prakash

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Comments

scorpiozj · Accepted Answer · 2012-05-14 07:14:53Z

0

I think giorashc's answer is correct. Your problem is using "=" for Array only makes the new one previousStateArray points to the same memory of setUpArray. In other words, previousStateArray is the same as setUpArray .

For more detail information , you should search deep & shallow copy.

answered May 14, 2012 at 7:14

scorpiozj

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Comments

Will Roberts · Accepted Answer · 2012-05-14 07:54:10Z

-1

You should also use if(0 == buttonCount) rather than if(buttonCount==0).

answered May 14, 2012 at 7:54

Will Roberts

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