Re: Newbie Memory Questions on a Code Fragment
Re: Newbie Memory Questions on a Code Fragment
- Subject: Re: Newbie Memory Questions on a Code Fragment
- From: Kenneth Bruno II <email@hidden>
- Date: Wed, 21 Jan 2009 10:07:41 -0500
On Jan 21, 2009, at 9:23 AM, James Cicenia wrote:
Here is some code I wrote for the appdelegate to initialize some
dictionaries and arrays:
My main question has to do with memory and releasing it. In my app
I will need listOfMonthNames for my popups
and will also need dictionaryOfProduceTypes to populate other
dependent popups.
...
-(void)initializeArraysAndDictionaries {
if(!listOfMonthNames){
NSArray *listOfMonthNamesTmp = [[NSArray alloc] initWithObjects:
@"January
",@"February
",@"March
",@"April
",@"May
",@"June
",@"July",@"August",@"September",@"October",@"November",@"December"];
// enumerate over items
printf( "----static array\n" );
[listOfMonthNames arrayByAddingObjectsFromArray:listOfMonthNames2];
// free memory
[listOfMonthNamesTmp release];
First of all, you probably should just use the localized list of month
names that you can get through NSDateFormatter:
NSDateFormatter *aFormatter = [NSDateFormatter new];
NSArray *listOfMonthNames = [[aFormatter standaloneMonthSymbols]
retain];
This will give you an NSArray populated with NSString objects that
contain the localized month names in the proper order. Notice that I
retained the NSArray object. I did this because it is given to me
autoreleased so if I want to own it I need to retain it. When I no
longer need it I'll just call release on the object, this would most
likely be done in the dealloc method of the class in which I
initialized my object.
if(!dictionaryOfProduceTypes){
// Create a distinct dictionary of types that hold an array of
subtypes per type.
// Types and subtypes are attributes of the ProduceItem object
dictionaryOfProduceTypes = [[NSMutableDictionary alloc] init];
...
[dictionaryOfProduceTypes release];
}
By releasing the dictionaryOfProduceTypes object you are giving up
control of the object and allowing it to be deallocated. This means
that the object that you just initialized won't be around when you
need it. You want to only call release when you are 100% sure that
you won't need the object any more or when you are cleaning up, such
as in the dealloc method for a class.
NSMutableArray *subtypes = [dictionaryOfProduceTypes
objectForKey:item.type];
...
[subtypes release];
The objecForKey method returns an autoreleased NSArray. This means
that its retain count is greater than zero for now, but it will be
decremented to zero at some point in the future. By calling release
on this object you are causing it to be over-released and even worse
this will happen at some apparently random time in the future.
You should only call release on objects that you have created through
methods that begin with alloc, new, or copy or objects that you have
previously called retain upon. I suggest that you review the Cocoa
Memory Management Rules to understand this further:
<http://developer.apple.com/documentation/Cocoa/Conceptual/MemoryMgmt/Tasks/MemoryManagementRules.html
>
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