IOS: Do i need to retain key in dictionary ios?

Question

I have dictionary in which i m storing

1)keys = which is string attribute of an "SimpleObject" with 'assign' property

--2) value = "SimpleObject"

NSMutableDictionary retains the object so im releasing the object. the key is present in the same object. The key is string.

Now do i need to explicitly retain the string key before add it to dict ?

Please show the actual code. `assign` causes slight concern... — trojanfoe, Sep 10 '13 at 15:58
@property (readwrite, nonatomic, assign) NSString * instanceId; [currentPlayerPlist setObject:myObject forKey:object.instanceId]; [object release]; [myObject release]; game crashes on after adding few objects. When i retain string crash stop. — tashfeen, Sep 11 '13 at 04:38

score 3 · Accepted Answer · edited May 23 '17 at 10:31

No, you do not need to explicitly retain the NSString, because your object already does that. Since the dictionary retains the object, the NSString is safe from being released prematurely.

Moreover, NSDictionary makes a copy of your string key, as a precaution against using a mutable object as a dictionary key (which is very bad). That's why you are free to change that key inside the object as you please. Of course that would not change the placement of the object inside the dictionary.

score 0 · Answer 2 · answered Sep 10 '13 at 16:00

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The answer is no. Whether or not you are using ARC. No.

answered Sep 10 '13 at 16:00

fresidue

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@property (readwrite, nonatomic, assign) NSString * instanceId; [currentPlayerPlist setObject:myObject forKey:object.instanceId]; [object release]; [myObject release]; game crashes on after adding few objects. When i retain string crash stop – tashfeen Sep 11 '13 at 04:57

score 0 · Answer 3 · answered Sep 10 '13 at 16:01

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No, you do not need to retain the keys (or the values) of an NSDictionary. This is because NSDictionary copies the key. When you retrieve an objects with objectForKey: isEqual: is used to determine which key refers to the object you passed in.

answered Sep 10 '13 at 16:01

Benedict Cohen

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It copies the key or conform NSCopy protocol. But this doesn't guarantee release or it does ? in my case it is release :( – tashfeen Sep 11 '13 at 05:31

score 0 · Answer 4 · answered Sep 11 '13 at 22:02

The basic rule in manual memory management in Cocoa is -- worry about what you're doing in that object or method; don't worry about what any other object is doing.

All you're doing is passing the key to a method of the dictionary. You are not storing it around anywhere. Whatever the dictionary does with it, it is responsible for the proper memory management. What it does is none of your business.

(There is a slight exception with blocks, in that you sometimes must copy them before passing to a type-agnostic method. But let's not worry about this for now.)

IOS: Do i need to retain key in dictionary ios?

4 Answers4