I have a lot of objects named _Obj_1, _Obj_2, etc...
And I want to release all.
I'm using KVC. In particular to release all, i use:
MyClass *obj = nil;
for ( int i=1 ; i<=14; i++ ) {
obj = [self valueForKeyPath:[NSString stringWithFormat:#"_Obj_%d", i]];
[obj release];
}
clang analyzer tell me for [obj release];
Incorrect decrement of the reference count of an object that is not
owned at this point by the caller?
How can I fix it?
It's not an ARC project.
This can be fixed very easily
If you don't own the object (you didn't call retain), don't release it!
Instead of having lots of variables with the same name, use an array to hold the objects. Then the releasing will be only the release of an array.
Related
I have the following variable defined:
#property (nonatomic, retain) NSMutableArray *arraySpeechSentences;
And I am trying to initialise it in the following way:
// Set the array of sentences to the stored array
NSMutableArray *speechSentences = [[NSMutableArray alloc] initWithArray:[tempDict objectForKey:key]];
arraySpeechSentences = speechSentences;
[speechSentences release];
When I try to call [arraySpeechSentences count] the application crashes. However, if I set the variable in the following way:
// Set the array of sentences to the stored array
NSMutableArray *speechSentences = [[NSMutableArray alloc] initWithArray:[tempDict objectForKey:key]];
self.arraySpeechSentences = speechSentences;
[speechSentences release];
I can call [arraySpeechSentences count] perfectly fine. I was under the impression that if you use self. it simply checks to see if variable is already set, and if so it will release the object before assigning it the new value. Have I got this wrong, and if so when should I be using self. to set values?
Thanks for any help,
Elliott
Using a setter (like self.foo = ... or [self setFoo:...]) does release the old value but it also retains the new value, which is needed in the example you give.
The issue is that you're alloc and init'ing your array, and then releasing it. This indicates you no longer need it. So, you should either use the setter (usually preferable) or don't release your array.
If you're not using ARC, you should type
arraySpeechSentences = [speechSentences retain];
because you're accessing the instance variable directly, which means the value of the instance variable arraySpeechSentences will be the address of the speechSentence object, which you just released, so which is an invalid pointer. The semantic you declared in the property doesn't have an effect on the instance variable itself.
When you type self.arraySpeechSentences, you're actually using a shortcut for the setter [self setArraySpeechSentences:speechSentences], which actually retains the value passed as parameter (if you synthesized the property, it is retained because you specified retain in the property declaration; if you wrote the accessor yourself, it is your job to ensure you retained the value).
I'll try to give a detail answer for this.
First when you use #property/#synthesize directive you create getter and setter methods around a variable.
In your case, the variable is called arraySpeechSentences (the compiler will create the variable for you) and you can access these methods (setters and getters) with self..
self.arraySpeechSentences = // something
is the same as
[self setArraySpeechSentences:something]; // setter
And
NSMutableArray* something = self.arraySpeechSentences;
is equal to
NSMutableArray* something = [self arraySpeechSentences]; // getter
In the first snippet of code
NSMutableArray *speechSentences = [[NSMutableArray alloc] initWithArray:[tempDict objectForKey:key]];
arraySpeechSentences = speechSentences;
arraySpeechSentences points to the same object speechSentences points to. But when you do [speechSentences release] you dealloc that object and now arraySpeechSentences is a dangling pointer. You receive a message sent to a deallocated instance I suppose. Try to enable Zombie to see it.
Speaking in terms of retain count, the array has a retain count of 1 when you do alloc-init.
But when you release it, the retain count goes to zero, the object doesn't exist anymore and you have a crash when you try to access arraySpeechSentences.
Instead, when you deal with properties, the policy applied to a variable is important. Since the property use a retain policy, when you set an object
self.arraySpeechSentences = // something
the retain count for the referenced object is increased. Under the hood, saying self.arraySpeechSentences = // something is equal to call the setter like
- (void)setArraySpeechSentences:(NSMutableArray*)newValue
{
// pseudo code here...
if(newValue != arraySpeechSentences) {
[arraySpeechSentences release];
arraySpeechSentences = [newValue retain];
}
}
The second snippet work since the retain count for your object is one when you do alloc-init, becomes two when you call self.arraySpeechSentences = and returns to one when you do the release. This time, the object is maintained alive since it has a retain count of 1.
If you have a property with a retain or copy policy, don't forget to release the object in dealloc like, otherwise you can have leaks.
- (void)dealloc
{
[arraySpeechSentences release];
[super dealloc];
}
To understand how Memory works I suggest to read MemoryManagement Apple doc.
P.S. Starting from iOS 5 there is a new compiler feature, called ARC (Automatic Reference Counting), that allows you to forget about retain/release calls. In addition, since it forces you to think in terms of object graphs, I suggest you to take a look into.
Hope that helps.
If I have an NSMutableArray of custom objects, how can I must easily clear the array without causing any memory issues? Assume that the custom object class has a dealloc method in it which correctly released an instance variables etc.
For example is it ok to use the NSArray "removeAllObjects" method?
If yes - how does this work - does "removeAllObjects" call the "dealloc" method on each object as it removes them
If no - what would be the easiest approach to use?
EDIT (after 4 replies) - One last question of clarification after the great replies - I'm still not quite sure about the instance variables/properties in my custom object that I have set to retain? These seem to be only released via the the "dealloc" method in my custom object class, where we do this manually along with [super release].
So if, re clearing an array, if I do a removeAllObjects, and then NSArray issues a "release" to my custom objects, but doesn't call "dealloc", then how do my instance variables get released?
removeAllObjects will remove the object from the array. This process will send a release message to the object and this will decrease its reference count. When the reference count reaches zero the object will be deallocated.
don't do it like this, because it will leak.
NSObject *object = [[NSObject alloc] init]; + 1
[array addObject:object]; + 1
[array removeAllObjects]; - 1
=======
= + 1 -> Leak
this is the correct way:
NSObject *object = [[[NSObject alloc] init] autorelease]; + 1 (from alloc) - 1 (from autorelease)
[array addObject:object]; + 1
[array removeAllObjects]; - 1
=======
= 0 -> Object will be deallocated
Instead of calling removeAllObjects you could just release the array. If an array is deallocated everything that's inside of it gets released and if there is no other reference to the object it will be deallocated.
Yep, just call removeAllObjects. Just to be sure, you don't call retain when you add an object to an array or when you create an array with objects. That's done for you automatically.
Regarding dealloc, again that will be done automatically, and you can't predict when.
The only thing you need to have in the dealloc is the array object itself. That is, assuming it's an instance variable or ivar?
To check everything is good, run the Analyzer using Product -> Analyze. And then give the app a profile in Instruments using the Leaks instrument to check that none of your code is causing any memory leaks.
Basically removeAllObjects method sends release message to all the objects. The release method decrements the objects reference count. And if the reference count of an object reaches 0 then the dealloc message will be sent to the object.
The answer to your question is calling [array removeAllObjects] is completely safe. By the way if you don't want the array anymore you can directly call [array release] which releases all its objects as well as the array.
The dealloc method is never called directly. Everything is done thru the retain/release mechanism (and the reference counting principle). So this is the release method that gets called, not the dealloc directly. The dealloc method is only called by the runtime if the last release call causes the reference counting (retainCount) of the object reaches zero, meaning that the object really is deallocated from memory as noone uses it anymore.
NSArray and all container classes in Cocoa (NSDictionary, NSSet, ...) do retain their values. So when you add an objet to a container like NSArray, it will retain that value. And when you remove that value (including when you call removeAllObjects") it will release it.
Memory Mgmt rules are easy to follow: but the only rule that matters it that you only have to call release or autorelease if you called alloc, retain or copy methods. That's always the responsability of the objet which did the alloc/retain/copy to call the release/autorelease. Never leave a alloc/retain/copy without a pending release/autorelease call to balance it (or you will have leaks), but on the other hand never call release/autorelease if you didn't do the alloc/retain/copy call yourself.
Good example 1:
MyClass* obj = [[MyClass alloc] init]; // here you do an alloc
[myArray addObject:obj]; // the NSArray "myArray" retains the object obj
// so now you can release it, the array has the responsability of the object while it is held in the array
[obj release]; // this release balance the "alloc" on the first line, so that's good
[myArray removeAllObjects]; // there the object held by the array receive a release while being removed from the array. As nobody retains it anymore, its dealloc method will be called automatically.
Good example 2:
MyClass* obj = [[MyClass alloc] init]; // here you do an alloc
[myArray addObject:obj]; // the NSArray "myArray" retains the object obj
// so now you can release it, the array has the responsability of the object while it is held in the array
[myArray removeAllObjects]; // there the object held by the array receive a release while being removed from the array. But your own code still retains a reference to it (because of the "alloc" on first line) so it won't be removed from memory right now
[obj release]; // this release balance the "alloc" on the first line, and as nobody retains the object anymore, its dealloc method will be called and it will be deallocated from memory
Good example 3:
MyClass* obj = [self getSomeObjectFromAnotherMethod]; // here you don't have an "alloc" on this line
[myArray addObject:obj]; // the array retains the object
[myArray removeAllObjects]; // the array release the object while it removes it from the array
// no need to call "release" here as there is no "alloc" done in the scope of this code
Bad example:
MyClass* obj = [self getSomeObjectFromAnotherMethod]; // here you don't have an "alloc" on this line
[myArray addObject:obj]; // the array retains the object
[myArray removeAllObjects]; // the array release the object while it removes it from the array
[obj release]; // Crash here! obj does not exists anymore and has been deallocated from memory before this line!
I'm new to cocoa / objective-c and i'm struggeling with the releases of my objects. I have the following code:
gastroCategoryList = [[NSMutableArray alloc] init];
for (NSDictionary *gastrocategory in gastrocategories) {
NSString *oid = [gastrocategory objectForKey:#"id"];
GastroCategory *gc = [[GastroCategory alloc] initWithId:[oid intValue] name:[gastrocategory objectForKey:#"name"]];
[gastroCategoryList addObject:gc];
}
The analyzer shows me that the "gastrocategory" defined in the for is a potential memory leak. But i'm not sure if i can release this at the end of the for loop?
Also at the following code:
- (NSArray *)eventsForStage:(int)stageId {
NSMutableArray *result = [[NSMutableArray alloc] init];
for (Event *e in eventList) {
if ([e stageId] == stageId) {
[result addObject:e];
}
}
return result;
}
The Analyzer tells me that my "result" is a potential leak. But where should I release this?
Is there also a simple rule to memorize when i should use assign, copy, retain etc. at the #property ?
Another problem:
- (IBAction)showHungryView:(id)sender {
GastroCategoriesView *gastroCategoriesView = [[GastroCategoriesView alloc] initWithNibName:#"GastroCategoriesView" bundle:nil];
[gastroCategoriesView setDataManager:dataManager];
UIView *currentView = [self view];
UIView *window = [currentView superview];
UIView *gastroView = [gastroCategoriesView view];
[window addSubview:gastroView];
CGRect pageFrame = currentView.frame;
CGFloat pageWidth = pageFrame.size.width;
gastroView.frame = CGRectOffset(pageFrame,pageWidth,0);
[UIView beginAnimations:nil context:NULL];
currentView.frame = CGRectOffset(pageFrame,-pageWidth,0);
gastroView.frame = pageFrame;
[UIView commitAnimations];
//[gastroCategoriesView release];
}
I don't get it, the "gastroCategoriesView" is a potential leak. I tried to release it at the end or with autorelease but neither works fine. Everytime I call the method my app is terminating. Thank you very much again!
In your loop, release each gc after adding it to the list since you won't need it in your loop scope anymore:
gastroCategoryList = [[NSMutableArray alloc] init];
for (NSDictionary *gastrocategory in gastrocategories) {
NSString *oid = [gastrocategory objectForKey:#"id"];
GastroCategory *gc = [[GastroCategory alloc] initWithId:[oid intValue] name:[gastrocategory objectForKey:#"name"]];
[gastroCategoryList addObject:gc];
[gc release];
}
In your method, declare result to be autoreleased to absolve ownership of it from your method:
NSMutableArray *result = [[[NSMutableArray alloc] init] autorelease];
// An alternative to the above, produces an empty autoreleased array
NSMutableArray *result = [NSMutableArray array];
EDIT: in your third issue, you can't release your view controller because its view is being used by the window. Setting it to autorelease also causes the same fate, only delayed.
You'll have to retain your GastroCategoriesView controller somewhere, e.g. in an instance variable of your app delegate.
BoltClock's answer is spot-on as to the first part of your question. I'll try to tackle the rest.
Assign is for simple, non-object types such as int, double, or struct. It generates a setter that does a plain old assignment, as in "foo = newFoo". Copy & retain will, as their names imply, either make a copy of the new value ("foo = [newFoo copy]") or retain it ("foo = [newFoo retain]"). In both cases, the setter will release the old value as appropriate.
So the question is, when to copy and when to retain. The answer is... it depends. How does your class use the new value? Will your class break if some other code modifies the incoming object? Say, for example, you have an NSString* property imaginatively named "theString." Other code can assign an NSMutableString instance to theString - that's legal, because it's an NSString subclass. But that other code might also keep its own reference to the mutable string object, and change its value - is your code prepared to deal with that possibility? If not, it should make its own copy, which the other code can't change.
On the other hand, if your own code makes no assumptions about whether theString might have been changed, and works just as well whether or not it was, then you'd save memory by retaining the incoming object instead of unnecessarily making a copy of it.
Basically, the rule, which is unfortunately not so simple sometimes, is to think carefully about whether your own code needs its own private copy, or can correctly deal with a shared object whose value might be changed by other code.
The reason you can release gc after it is added to the gastroCategoryList is that when an object is added to an array, the array retains that object. So, even though you release your gc, it will still be around; retained by the gastroCategoryList.
When you are returning a newly created object from a method, you need to call autorelease. This will cause the object to be released only after the runtime leaves the scope of the calling method, thereby giving the calling method a chance to do something with the returned value.
Note that if your method starts with the word copy or new, then you should not autorelease your object; you should leave it for the calling method to release.
As for copy vs retain vs assign... as a general rule, copy objects that have a mutable version, such as NSArray, NSSet, NSDictionary, and NSString. This will ensure that the object you have a pointer to is not mutable when you don't want it to be.
Otherwise, use retain whenever you want your class to be ensured that an object is still in memory. This will apply to almost every object except for objects that are considered parents of your object, in which case you would use assign. (See the section on retain cycles here).
Also note that you have to use assign for non-object types such as int.
Read through the Memory Management Programming Guide a bit; it's quite helpful.
i wrote this code :
bs = [NSNumber numberWithFloat:[mystring.text floatValue]];
NSLog(#"bs = %#",bs);
....
float x = [bs floatValue];
when the program want to excute the line above it crash why ?
the output :
bs = 2.8 which true 100%
Between the time you assigned an NSNumber object to your ivar bs it was release by the runtime. I am assuming where you created bs and where you try to assign it to x are in two different methods. If that is the case, you need to tell the runtime you want to keep the ivar bs around for awhile:
[bs retain];
And if you do that, you need to tell the runtime you are done in the dealloc:
-(void)dealloc {
[bs release];
[super dealloc];
}
Basically, if you didn't create an object with alloc, copy, mutableCopy, new in the method name, then you don't own the object.
the code snippet seems ok.
and I guess the reason is bs was released before fetching its float value.
the simplest way to retain bs is to change it to a property:
#property (nonatomic,retain)NSNumber* bs;
and release it in dealloc
Hi I have a lot of problems to remove the objects of my mutable array.
I have a method which send back a mutable initialized with a custom object.
This mutable is declared like autorelease for releasing after method.
In my return, I retain the mutable to not loose it.
I want in this second method to remove the content of my mutable and release my mutable.
But my app quit and fail.
//first method which return my mutable
NSMutableArray *highScores = [[[NSMutableArray alloc] init]autorelease] ;
for (....)
{
HighScore *currentHighScore = [[HighScore alloc] init];
currentHighScore.user = name;
currentHighScore.score = score;
//add to the array
[highScores addObject:currentHighScore];
[currentHighScore release];
}
return highScores;
// method which use the first method
//retrieve with retain to keep.
highScoreList = [[HighScoreViewController getHighScores:NormalGameModeXML]retain] ;
HighScore *currentHighScore;
int count = [highScoreList count];
for (int i = 0; i < count ; i++)
{
currentHighScore = [highScoreList objectAtIndex:i];
}
This is working, but off course I have memory leak for all the objects in the mutable not released.
But if i'm trying to release the object of the mutable and the mutable itself by this :
//remove Mutable array content.
//[highScoreList removeAllObjects] ;
//[highScoreList release];
My app is quitting.
Do you have a solution to avoid the memory leak and clean it well?
Try using NSZombieEnabled to check the reason for an EXC_BAD_ACCESS..
HowTo is found here..
//[highScoreList removeAllObjects] ;
//[highScoreList release];
No need to removeAllObjects prior to release.
Note that if you use highScoreList after it is deallocated, your app will crash as you describe. I.e. if you use highScoreList after the above, BOOM.
You could set highScoreList to nil, but a better solution is to understand why you are using an object after you think you should be done with it.
And, as always:
If there is a crash, there is a backtrace. Post it.