Hi,
On Mar 24, 2008, at 11:19 PM, Samvel wrote:
Lots of classes define static methods that create objects for
instance:
Class NSString:
+(id) stringWithString: (NSString *) string;
or Class NSArray:
+(id) arrayWithObjects: (id) firstObj, ...;
A minor nit-pick about terminology: these methods are not called
"static methods" in Objective-C. They are "class methods".
I am really confused about next situation and memory management of
objects created via those methods. Please, explain.
Imagine class with
NSString *string;
instance variable. I create it and initiate with method above in:
-(id) init;
of my class. Now, want to use this string in another method
sometime later, say in:
-(void) plug;
Should I retain string in init?
Yes. By convention, the class methods you refer to -- known as
convenience methods -- return autoreleased objects. That means that,
if you don't do anything to keep them around, they will be released
automatically at some future time. When exactly is an implementation
detail, but you can only rely on them lasting until the current call
stack returns out of your code.
Since your object needs the string referred to by its instance
variable to last for a a different period of time, it needs to retain
the string to guarantee that.
e.g.:
-(id) init
{
// ...
string = [NSString stringWithString: @"hello"];
[string retain];
// ...
}
That's one way of doing it. Another way would be for the init method
to call your setter for that property (if one exists). Since the
setter should already have proper memory management, you won't have
to worry about this as a separate case.
-(void) dealloc
{
// ...
[string dealloc];
// ...
}
The above is wrong. You should never explicitly invoke "dealloc" on
an object (except doing [super dealloc] as part of your own dealloc
implementation). When your object is deallocated, it doesn't know
that the string should also be deallocated. It just knows that it
doesn't need the string to stick around anymore. (Something else
might need the string.) So, your object should just release the string.
Cheers,
Ken
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