I have tried to use the Analyze instrument to see the memory leaks, and Xcode gives me a memory leak in this point:
.h
#property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
.m
#synthesize managedObjectContext = __managedObjectContext;
then in the code I do this:
AppDelegate *appController = [[UIApplication sharedApplication] delegate];
self.managedObjectContext = [[NSManagedObjectContext alloc] init];
[self.managedObjectContext setUndoManager:nil];
[self.managedObjectContext setPersistentStoreCoordinator: [appController persistentStoreCoordinator]];
and in the dealloc this:
- (void)dealloc
{
[__managedObjectContext release];
[super dealloc];
}
It gives me a memory leak on this line:
[self.managedObjectContext setUndoManager:nil];
for this object:
self.managedObjectContext = [[NSManagedObjectContext alloc] init];
I have released it in the dealloc, why a memory leak there?
Your _managedObjectContext leaks because its retain count is increased twice, but you only release it once. You have made your property strong which means it will retain the object when it is assigned to it. But you also allocate managedObjectContext without autoreleasing (or manually releasing) it. Hence the error is in this line:
self.managedObjectContext = [[NSManagedObjectContext alloc] init];
The object you allocate will have a retain count of 1, but the synthesized property will retain it one more time, hence giving it a retain count of 2. When you release it in dealloc, it will stay around since it still has a retain count of 1.
What you need to do is either autorelease the object you allocate:
self.managedObjectContext = [[[NSManagedObjectContext alloc] init] autorelease];
or not call the synthesized setter, but assign directly to _managedObjectContext:
_managedObjectContext = [[NSManagedObjectContext alloc] init];
I would recommend the former since the latter will leak if _managedObjectContext is not nil. However if you're sure _managedObjectContext is nil before the assignment, you can pick either one you want.
This line...
self.managedObjectContext = [[NSManagedObjectContext alloc] init];
...increases the retain count by two, one for the alloc and one for the "strong" on the property.
Try:
__managedObjectContext = [[NSManagedObjectContext alloc] init];
Related
I know that when we add an object obj into a NSMutableArray, it takes the co_ownership of that object. So we can release the object obj just after adding that into the NSMutableArray. And when we release the NSMutableArray, it also calls the release of all the objects in it. So there is no memory leak and every thing is fine.
My doubt is if do like
NSMutableArray myArray = [[NMutableArray alloc] init];
[myArray addObject:[MyClass alloc] init]];
[myArray release];
Will this Cause any memory leak in our program?
Yes indeed, it will cause a memory leak.
The offensing line is (I have splitted it for clarity):
[myArray addObject:
[[MyClass alloc] init] // <- An instance is allocated with ownership
]; // <- The array retains the instance
At the end, the retain/release ownership are not balanced and causes the leak.
One solution is to make the allocation before the addition:
MyClass *obj = [MyClass alloc] init];
[[myArray addObject:obj];
[obj release];
Put autorelease for your MyClass. That should fix any memory leaks
NSMutableArray myArray = [[NMutableArray alloc] init];
[myArray addObject:[[[MyClass alloc] init] autorelease];
[myArray release];
I am very new at this and seems to have a leak in this piece of code that i cannot fix:
The Instruments shows on this line with a 100%:
NSMutableArray *read_Question = [[NSMutableArray alloc] initWithCapacity: 0];
I have tried all kind of things but not been able to fix it.
Anyone nice that can advice me how to proceed?
- (NSMutableArray *)readQuestion: (int)questionNr {
NSMutableArray *read_Question = [[NSMutableArray alloc] initWithCapacity: 0];
NSError *error;
//=========PREPARE CORE DATA DB===========//
if (managedObjectContext == nil) {
managedObjectContext = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; }
// Define qContext
NSManagedObjectContext *qContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"questions" inManagedObjectContext:qContext];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [qContext executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *info in fetchedObjects) {
if ([[info valueForKey:#"idQ"] intValue] == questionNr) {
[read_Question addObject:[info valueForKey:#"question"]];
[read_Question addObject:[info valueForKey:#"qRightAnswer"]];
[read_Question addObject:[info valueForKey:#"qWrongAnswer1"]];
[read_Question addObject:[info valueForKey:#"qWrongAnswer2"]];
}
}
[fetchRequest release];
return [read_Question autorelease];
}
It seams that you are returning the object only inside the if statement. Meaning that if the if statement is false you will not autorelease the array. Or maybe you didn't paste the entire method. Let me know. Instruments is sometimes tricky.
This is a dupe of your other question Memory leak problem and i need help #1
When i did release i got into trouble,
of course. I did try to change the
names on the three and do release so
there was unique names but that did
not work.
Changing the names across three different files? That won't do anything and it indicates that you haven't entirely wrapped your head around objects, pointers, and memory management.
The Objective-C and Memory Management guides will help.
Could this be the reason for the leak
i have in this .m file?
Nope -- as I answered in the other question, the leak is most likely because you retain the object that is returned by that method and then don't release it anywhere.
Instruments is telling you were the leaked object was allocated, not where it was necessarily leaked.
While you may not be autoreleasing the array in all cases on return from that method, you might also be retaining it somewhere else and not balancing that retain with a release.
I am assuming you set the property managedObjectContext to "retain". Change the line to this (include "self" so that it gets retained):
if (self.managedObjectContext == nil) { self.managedObjectContext = [(FamQuiz_R0_1AppDelegate *)
[[UIApplication sharedApplication] delegate] managedObjectContext]; }
Then add your release back in.
Since I believe the code from picciano will fix the issue of the openingsposter, here a small explanation why it should fix the issue.
If you give a property the retain attribute, it will create an accessor method that looks somewhat like this (simplified):
#property (nonatomic, retain) NSValue *value;
- (void)setValue:(NSValue *)aValue {
value = [aValue retain];
}
Only when the retainCount reaches 0 an object is released, using retain, alloc and copy increases the retainCount. Remember: only when using the accessor method the retain actually happens (besides using alloc, retain and copy directly). The accessor method is usually called when using one of the following methods:
// the 2 most obvious ways to call the accessor methods ...
object.value = someValue;
[object setValue:someValue];
You created a retain property in your code, yet you didn't use the accessor method, so the object was never retained.
// no accessor used here ...
managedObjectContext = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
If you would release it from this point on, it would cause a crash, since the retainCount would actually become -1 at some point (since it never got to 1 in the first place). Therefore you should set the property like this:
// the dot-notation syntax to make use of the accessor method ...
self.managedObjectContext = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
or (in my opinion preferably):
// making use of the accessor method directly, which is very unambiguous ...
NSManagedObjectContext *context = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
[self setManagedObjectContext:context];
This way you can be sure the retain actually happens.
The second notation to accessor setters is in my opinion superior and I consider it good habit to use it for setting properties whenever possible. Read more about people who share this opinion and their reasoning on the following sites:
Cocoa Is My Girlfriend
The Big Nerd Ranch
I am very new at this and seems to have a leak in this piece of code that i cannot fix:
The Instruments shows on this line with a 100%:
NSMutableArray *read_Question = [[NSMutableArray alloc] initWithCapacity: 0];
I have tried all kind of things but not been able to fix it.
Anyone nice that can advice me how to proceed?
- (NSMutableArray *)readQuestion: (int)questionNr {
NSMutableArray *read_Question = [[NSMutableArray alloc] initWithCapacity: 0];
NSError *error;
//=========PREPARE CORE DATA DB===========//
if (managedObjectContext == nil) {
managedObjectContext = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; }
// Define qContext
NSManagedObjectContext *qContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"questions" inManagedObjectContext:qContext];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [qContext executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *info in fetchedObjects) {
if ([[info valueForKey:#"idQ"] intValue] == questionNr) {
[read_Question addObject:[info valueForKey:#"question"]];
[read_Question addObject:[info valueForKey:#"qRightAnswer"]];
[read_Question addObject:[info valueForKey:#"qWrongAnswer1"]];
[read_Question addObject:[info valueForKey:#"qWrongAnswer2"]];
}
}
[fetchRequest release];
return [read_Question autorelease];
}
It seams that you are returning the object only inside the if statement. Meaning that if the if statement is false you will not autorelease the array. Or maybe you didn't paste the entire method. Let me know. Instruments is sometimes tricky.
This is a dupe of your other question Memory leak problem and i need help #1
When i did release i got into trouble,
of course. I did try to change the
names on the three and do release so
there was unique names but that did
not work.
Changing the names across three different files? That won't do anything and it indicates that you haven't entirely wrapped your head around objects, pointers, and memory management.
The Objective-C and Memory Management guides will help.
Could this be the reason for the leak
i have in this .m file?
Nope -- as I answered in the other question, the leak is most likely because you retain the object that is returned by that method and then don't release it anywhere.
Instruments is telling you were the leaked object was allocated, not where it was necessarily leaked.
While you may not be autoreleasing the array in all cases on return from that method, you might also be retaining it somewhere else and not balancing that retain with a release.
I am assuming you set the property managedObjectContext to "retain". Change the line to this (include "self" so that it gets retained):
if (self.managedObjectContext == nil) { self.managedObjectContext = [(FamQuiz_R0_1AppDelegate *)
[[UIApplication sharedApplication] delegate] managedObjectContext]; }
Then add your release back in.
Since I believe the code from picciano will fix the issue of the openingsposter, here a small explanation why it should fix the issue.
If you give a property the retain attribute, it will create an accessor method that looks somewhat like this (simplified):
#property (nonatomic, retain) NSValue *value;
- (void)setValue:(NSValue *)aValue {
value = [aValue retain];
}
Only when the retainCount reaches 0 an object is released, using retain, alloc and copy increases the retainCount. Remember: only when using the accessor method the retain actually happens (besides using alloc, retain and copy directly). The accessor method is usually called when using one of the following methods:
// the 2 most obvious ways to call the accessor methods ...
object.value = someValue;
[object setValue:someValue];
You created a retain property in your code, yet you didn't use the accessor method, so the object was never retained.
// no accessor used here ...
managedObjectContext = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
If you would release it from this point on, it would cause a crash, since the retainCount would actually become -1 at some point (since it never got to 1 in the first place). Therefore you should set the property like this:
// the dot-notation syntax to make use of the accessor method ...
self.managedObjectContext = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
or (in my opinion preferably):
// making use of the accessor method directly, which is very unambiguous ...
NSManagedObjectContext *context = [(FamQuiz_R0_1AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
[self setManagedObjectContext:context];
This way you can be sure the retain actually happens.
The second notation to accessor setters is in my opinion superior and I consider it good habit to use it for setting properties whenever possible. Read more about people who share this opinion and their reasoning on the following sites:
Cocoa Is My Girlfriend
The Big Nerd Ranch
I'm trying to resolve a memory leak but I can't find any solution.
Instruments says that there is a leak in this method:
- (void)refreshData {
Sn0werSp33dAppDelegate *appDelegate = [[Sn0werSp33dAppDelegate alloc] init];
NSFetchRequest *coreDataNewsFetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"News" inManagedObjectContext:managedObjectContext];
[coreDataNewsFetchRequest setEntity:entity];
self.managedObjectContext = appDelegate.managedObjectContext;
self.newsArray = [[managedObjectContext executeFetchRequest:coreDataNewsFetchRequest error:nil] mutableCopy];//Intruments says that here is the memory leak :(
[appDelegate release];
[coreDataNewsFetchRequest release];
[entity release];
}
newsArray is declared in my .h as an NSMutableArray and it has a property:
#property (nonatomic, retain) NSMutableArray *newsArray;
I've tried many things but at all times, that things weren't working.
I'm running XCode 3.2.5 with iPhone SDK 4.2.1 and Instruments 2.7.
When you do
self.newsArray = something;
that something is retained, because you added retain to the newsArray property.
But mutableCopy also returns an object with a retain count increased by 1. So after the method finishes, your newsArray has a retain count one higher than what you really want, which is the memory leak that was detected.
Solution: Replace the line where you assign self.newsArray with
self.newsArray = [[[managedObjectContext executeFetchRequest:coreDataNewsFetchRequest error:nil] mutableCopy] autorelease];
mutableCopy makes a copy and retains it, so you need to release the copy you've created. Try changing this:
self.newsArray = [[managedObjectContext executeFetchRequest:coreDataNewsFetchRequest
error:nil] mutableCopy];
To this:
self.newsArray = [[[managedObjectContext executeFetchRequest:coreDataNewsFetchRequest
error:nil] mutableCopy] autorelease];
As an aside, creating a new object of your app delegate class is a little unusual and might not give you the result you expect. Conventionally you instantiate one app delegate (by default this is done for you in MainWindow.xib) and then refer to it throughout your app using:
FooAppDelegate *appDelegate = (FooAppDelegate*)[[UIApplication sharedApplication] delegate];
I have a question about reference counting.
This is my constructor:
- (id)initWithId:(NSString *)graphId;
In another class I make an object in the following way:
GraphViewController *graph =
[[GraphViewController alloc] initWithId:[[NSString alloc] initWithFormat:#"%s", current_ID];
My question is: how do I correctly release the string object?
Is it correct to release the string passed as a parameter?
Any of these ways will work:
(1)
GraphViewController *graph = [[GraphViewController alloc] initWithId:
[[[NSString alloc] initWithFormat:#"%s", current_ID] autorelease]];
(2)
GraphViewController *graph = [[GraphViewController alloc] initWithId:
[NSString stringWithFormat:#"%s", current_ID]];
(3)
NSString *aString = [[NSString alloc] initWithFormat:#"%s", current_ID];
GraphViewController *graph = [[GraphViewController alloc] initWithId: aString];
[aString release];
And, of course, graph needs to be released or autoreleased somewhere.
Never pass ownership around. I.e., in your call to initWithId: you create a string. Make sure it's released in the exact same place. Do not hand the ownership over, burdening another function with the task of releasing what you created (or retained, ...).
If you're not calling initWithId: an unusually high number of times per second, do an autorelease. Even better, use a convenience function. Do not let people talk you into "avoiding the autorelease pool". Because a) it's not so easy to avoid and b) you have more important things to worry about.
In code:
NSString* graphID = [NSString stringWithFormat: #"%s", current_ID];
GraphViewController* graph = [[[GraphViewController alloc] initWithId: graphID] autorelease];
In the constructor, you will simply retain the ID and in the dealloc you will release it again. And please... use (private) #property declarations for this. You can then completely remove the ivar "graphID" from your public interface (if it's private, of course).
#interface GraphViewController ()
#property (copy, nonatomic) NSString* graphID; // copy instead of retain for potentially mutable objects
#end
Then, in initializer and dealloc, boilerplate stuff like:
#synthesize graphID;
- (id)initWithId:(NSString*) ID;
{
self = [super init];
self.graphID = ID;
return self;
}
- (void) dealloc
{
self.graphID = nil; // controversial, Apple policy is [graphID release]; graphID = nil;
[super dealloc];
}
Using this style will make you sleep better at night. Delighted users will raise statues in your name.