Creating a NSMutableArray to hold pointers

Question

I am trying to create a mutable array in objetive c to hold references to objects. The objects in the array are regularly updated through user interaction and i want the array to automatically reflect changes made to the objects as they occur. Does anyone know if there is a way to do this? Perhaps store pointers to the objects instead of the objects themselves in the array? Any help would be much appreciated

Thanks in advance

Edit: I should mention that the objects are not exactly being updated in the strict sense of the word. They are being reinitialized. For ex if i had a controller:

MyController = [MyController alloc] initWith.....]]

the above call is made again with different init parameters.

array is just a container that stores data. You need to set a delegate for each object that will receive updates. — Max
– Max, Commented Dec 5, 2012 at 20:57

Mario · Accepted Answer · 2012-12-05 21:19:13Z

4

The array always stores the pointers.... It holds a strong reference to it or sends it a retain message (if using non ARC).

So

[myMutableArray addObject: anObject];

adds the pointer to it.

If you now change anObject's properties and access it later through the array, it will give you the pointer to just that object with the changes to its properties.

Edit:

No, if you alloc/init, you are creating a new object instance and allocate new memory for it on the heap (ie, it's another pointer to a new memory address). What exactly are you trying to accomplish? There sure is a way, if you provide a little more detail.

If you alloc/init the object with the same class, why not just create a method to change the object's properties:

Instead of

myObject = [[MyClass alloc] initWithParameter1: one parameter2: two];

You could create a method that changes these properties:

[myObject updateParameter1: anotherOne parameterTwo: anotherTwo];

And, of course, the advantage of a mutable array is, that you can change its contents, so like @Eli Gregory pointed out, you can replace an object with another one (or rather the pointers to it).

edited Dec 5, 2012 at 21:19

answered Dec 5, 2012 at 20:56

Mario

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5 Comments

Taum Over a year ago

The problem I believe is OP is creating a new instance, not just changing properties of the same object (what he calls "reinitializing").

John Baum Over a year ago

im not sure if its a new instance or not but it is assigned to the same property

John Baum Over a year ago

essentially i have an array of controllers for a page. once the user makes edits a cell on that page and goes back to the page, each controller is reinitialized with new data to display such as more cells per section depending on the user response. I want to be able to keep an array of these controllers referring to the correct objects

bbum Over a year ago

im not sure if its a new instance or not There is your problem. You need to take a step back and understand how object references and alloc works.

John Baum Over a year ago

once i have modified the parameter, the reference to the object should remain the same correct? so the array will now still hold the same reference, the difference being that the controller's property will now have changed?

esreli · Accepted Answer · 2012-12-05 21:13:59Z

0

Because you want to point to a newly allocated and initialized object, you can't 'update' the pointer, what you can do is 'replace' the pointer with a new one at a certain index.

A method you could use to do this is:

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject

so it would look something like:

NewViewController *new = [[NewViewController alloc] init..];
[myArray replaceObjectAtIndex:x withObject:new];

answered Dec 5, 2012 at 21:13

esreli

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1 Comment

John Baum Over a year ago

yes but then i would need a reference to the stale entry in the array in order to replace it with a new reference

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