NSMutableArray of NSMutableArrays, addObject problem

Question

I'm relatively new to objective-C and I'm having a problem with a 2D NSMutableArray and it's behaviour when adding the contents of one NSMutableArray to another.

I have a singleton class containing an NSMutableArray. This array is for storing NSURL values. At a certain point in my program, I need to add this NSMutableArray as a whole to another NSMutableArray.

I do something like this: [arrayIWantStuffIn addObject: mySingleton.singletonMutableArray];

The problem I have is that I need to reset my singltonMutableArray to start storing a new set of NSURL values. The addObject function above appears to be passing by reference rather than passing by value, so when I do:

[mySingleton.singletonMutableArray removeAllObjects];

The data stored in arrayIWantStuffIn is wiped as well.

How can I achieve a 'deep' addObject that is adding a NSMutableArray to another NSMutableArray by value and not by reference?

Joe · Accepted Answer · 2011-08-12 15:55:43Z

0

You dont actually need a deep copy just another mutableCopy. This can be done simply by doing the following

[arrayIWantStuffIn addObject: [[mySingleton.singletonMutableArray mutablCopy] autorelease]];

Once that is done when the singletonMutableArray is cleared or changed it will not change your items in arrayIWantStuffIn and you can still modify the contents independently.

answered Aug 12, 2011 at 15:55

Joe

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2 Comments

Drew_TwistedPair Over a year ago

That worked like a charm. Thanks Joe. Just the make sure I'm understanding this correctly, the [mySingleton.singletonMutableArray mutableCopy] makes a deep copy of my singletonMutableArray and then uses that copy as the object passed to addObject?

Joe Over a year ago

It will not make a deep copy of your singletonMutableArray so the mutableCopy will still point to the same NSURL's at the time of the copy but when you make changes to singletonMutableArray it will not change your arrayIWantStuffIn and vice versa. Also NSURL's are immutable so you do not have to worry about those changing.

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