I have an NSString called animation, which is called with the following (working) code:
animation=[rowInDataBase objectAtIndex:2] ;
NSLog(#"animation:%#",animation);
When I try to perform the following :
previousAnimation=animation;
The previousAnimation is assigned ccsprite.
When I try to logging previousAnimation to check its value with NSLog(#"previous-animation:%#",previousAnimation);, the application crashes unless previousAnimation is NULL
What am I doing wrong in my assignment ?
animation needs to be properly retained. You should create a property with a retain attribute for animation and previousAnimation and set them like this.
self.animation = [rowInDatabase objectAtIndex:2];
...
self.previousAnimation = self.animation;
Now both values will be properly retained between calls you will no longer have crashing issues. Just remember to release both values in dealloc.
Are you trying to copy the string? If so you should be doing:
NSString* previousAnimation = [NSString stringWithString:animation]; // autoreleased
or
NSString* previousAnimation = [animation copy]; // retain count 1, need to release
otherwise you should retain
previousAnimation = [animation retain];
and release previousAnimation when you are done.
It sounds like you're assigning a variable that has already been released, so the memory's being reused by some other random object (in the case you mentioned, a ccsprite object perhaps). But it's hard to tell for sure without seeing the code in more context.
Related
I have a method call in class A:
GDataXMLElement *infoElement = [self getElementFromFilePath:filePath];
NSString *testStringA = [infoElement attributeForName:#"someAttribute"].stringValue;
and the method implementation in class B:
-(GDataXMLElement*)getElementFromFilePath:(NSString*)filePath {
NSData *xmlData = [NSData dataWithContentsOfFile:filePath];
GDataXMLDocument *infoXMLDoc = [[GDataXMLDocument alloc] initWithData:xmlData options:0 error:nil];
NSArray *infoArray = [infoXMLDoc.rootElement elementsForName:#"test"];
GDataXMLElement *returnElement = (GDataXMLElement*)infoArray[0];
NSString *testStringB = [returnElement attributeForName:#"someAttribute"].stringValue;
return returnElement;
}
The returnElement at the end of the method in class B is perfectly initialized, and testStringB string contains the correct value.
But in Class A, the contents of InfoElement are gone, and testStringA is nil.
I suspect that ARC is releasing GDataXMLDocument too early, and was able to stop this behaviour by tying the document to a property in class B:
#property (nonatomic,strong) GDataXMLDocument *infoXMLDoc;
But I am a little unsatisfied with this solution. I'll never use that property again, I just need the element to parse it one time only. If it is possible to stop the release with a property, is there also a way to do this within the method? I tried the __strong qualifier like this:
GDataXMLDocument __strong *infoXMLDoc = [[GDataXMLDocument alloc] initWithData:xmlData options:0 error:&error];
but that didn't help. So my questions, assuming ARC is indeed responsible:
1. Is is possible to tell ARC within a method to not release an object?
2. What did I not understand about the behaviour here? I am using ARC for some time now, this is the first time that I am stuck.
The GDataXMLNode.h header says:
it is up to the code that created a document to retain it for as long
as any references rely on nodes inside that document tree.
The node you return from getElementFromFilePath depends on the parent (the GDataXMLDocument), but that is going to be released by ARC. You must retain the GDataXMLDocument somewhere for as long as you reference nodes and elements inside it. These are the semantics of the GDataXML* classes and you must follow them.
I can't compile so this's just an educated guessing, but I suspect the problem is that you return a pointer to an object that is allocated and released inside the method:
GDataXMLElement *returnElement = (GDataXMLElement*)infoArray[0];
As you see you don't alloc returnElement, so ARC have no way to understand that you need it. It simply release infoArray when you exit from the method.
If you copy the value (something like [(GDataXMLElement*)infoArray[0] copy] ) it should works.
According to the static analyzer if we have the following property:
#property (retain, nonatomic) SomeObject * object;
and then we assign the property like so:
self.object = [SomeObject alloc] init];
a leak occurs. This makes sense because the alloc init adds +1 to the retain count and then the retaining property also increments the retain count. What is the best solution here? typically I just add an autorelease like so:
self.object = [[SomeObject alloc] init] autorelease];
But sometimes this creates problems for me and I end up over releasing the object causing my app to crash. I don't have any specific examples right now but I remember I had to take out some autoreleases cause of the application crashing. Is there something I am missing here?
EDIT: I have a concrete example now of the issue I was running into.
NSMutableArray *newData = [NSMutableArray array];
//If this is true then we are showing all of the items in that level of hierarchy and do not need to show the summary button.
if (!(contextID.count >= 1 && [[contextID objectAtIndex:contextID.count - 1] isEqual:[NSNull null]]) && contextID.count != 0)
{
GeographyPickerItem * firstItem = [[GeographyPickerItem alloc] init];
firstItem.primaryString = [NSString stringWithString:#"Summary"];
firstItem.subString = [NSString stringWithString:#""];
firstItem.isSummaryItem = YES;
[newData addObject:firstItem];
[firstItem release]; //TODO: Figure out why this is causing EXC_BAD_ACCESS errors
}
self.hierData = newData;
The code above is in the init method of a viewcontroller. HierData is a retained property, which is released in the viewControllers dealloc method. GeographyPickerItem retains the two strings, primaryString and subString and releases them in its own dealloc method. My application crashes (sometimes) when the viewControllers are de-alloced following a pop off of a navigation controller. It crashes with a EXC_BAD_ACCESS signal in the dealloc method of GeographyPickerItem (either on [substring release] or [primaryString release]).
I don't understand why this is happening because I believe I am following proper memory management guidelines. If I comment out firstItem release everything is fine.
The autorelease method you mention is fine, as is the other common idiom of:
SomeObject *thing = [[SomeObject alloc] init];
self.object = thing;
[thing release];
If you end up overreleasing later on, that is your problem. This part, which you're apparently doing correctly, is not the problem.
SomeObject * new_object = [SomeObject alloc] init];
self.object = new_object;
[new_object release];
or use ARC
check the GeographyPickerItem, if the strings properties are assign (and change to retain), or check if you always initialize them (before release).
also remember the difference of manually allocating :
[[NSString alloc] initWith...]
You must release or autorelease.
[NSString stringWith...]
No need to release.
or use ARC like meggar said
Turns out the issue was simple, my dealloc method called super dealloc at the start of the method rather than at the end. You always have to release your instance variables before you call [super dealloc]!
I think I understand retain/release in objective-C for the most part. However, I have a specific case I am unsure about. Here is an example:
+ (NSString *)getPlayerNameByIndex:(NSInteger)globalIndex:(ABAddressBookRef)addressBook
{
...
Player *player = [PlayerHelper loadPlayer:globalIndex];
NSString *name = [PlayerHelper getPlayerName:player :addressBook];
[player release];
// 'retain' here?
return name;
}
+ (NSString *)getPlayerName:(Player *)player:(ABAddressBookRef)addressBook
{
...
NSString *name = [[[NSString alloc] initWithString:player.nickname] autorelease];
return name;
}
So then I call...
NSString *name = [PlayerHelper getPlayerNameByIndex:index:addressBook];
// name is 'autorelease'?
What I saw on random occasions is that the view sometimes shows the 'name' field as empty when it populates the table after coming back from another view. This could be another issue but I want to be sure of my use of 'autorelease'.
The core of my question is the use of 'autorelease' in getPlayerName. Does the 'autorelease' state of being get passed through method getPlayerNameByIndex to the caller?
Or, do I have to call 'retain' in the intermediary method? I am thinking 'autorelease' may be releasing in method getPlayerNameByIndex.
Hopefully my question is clear. Any help is appreciated.
Update: Some more info for clarification...
NSError *error = nil;
Player *player = nil;
NSArray *array = [appDelegate.managedObjectContext executeFetchRequest:request error:&error];
if ([array count] == 1)
{
player = [array objectAtIndex:0];
[player retain];
}
This is essentially the "loadPlayer" method which loads info from core data. From the answers it sounds like I do not need to call [player retain], since it is an autorelated object, and I can simply return "player" and use it? Thanks for the responses!
The core of my question is the use of 'autorelease' in getPlayerName. Does the 'autorelease' state of being get passed through method getPlayerNameByIndex to the caller?
The answer is yes.
Or, do I have to call 'retain' in the intermediary method?
whether you want to call retain depends on the semantics of your method.
In Obj-C/Cocoa, the following convention applies: a method whose name begins with “alloc” or “new” or contains “copy” will return a retained object; otherwise you can expect to get an autoreleased object, then it is the caller responsibility to retain it according to its needs.
I am thinking 'autorelease' may be releasing in method getPlayerNameByIndex.
autoreleased objects are released at the next point in time when the autorelease pool is drained; this is usually associated to going back to the main loop (though, no details are available about this); so you can be pretty sure that auto-releasing does not kick in in getPlayerNameByIndex...
Hope this helps clarifying the issue...
In getPlayerNameByIndex The line:
[player release];
is wong, remove it. You did not obtain ownership. Ownership is ob gained by calling a method with alloc or the method names starts with new, copy or an explicit retain. (NARC).
You do not need to release player because you did not obtain ownership, see above rule.
In getPlayerName:
can be simplified to:
return player.nickname;
The method name can be simplifies to:
+ (NSString *)getPlayerName:(Player *)player
If I set a NSString as property
#property (copy) NSString* name;
I always want to use (copy), so that if its value change, all object with such string still have the old value (as specifiedhere).
However, what happens if my NSString is not a class property, but it is just declared in the code ? Is in that case retained or copied everytime I assign a new value ?
thanks
It depends on how you declare it. You should read the documentation on memory management. Basically the rules are:
NSString *aString = [NSString stringWithString:#"Hello"];
NSString *bString = [NSString stringWithFormat:#"%#", #"Hello"];
In these cases, the string is not copied or retained. It is autoreleased, which means it will be automatically deallocated the next time the autorelease pool drains. You do not have to call the release method on them. (So assigning a new value will not cause it to leak.)
NSString *cString = [[NSString alloc] initWithFormat:#"%#", #"Hello"];
[cString release];
According to Objective C convention, methods that use alloc and have a retain count of one are not autoreleased, so you need to release them explicitly. Assigning a new value without releasing the old one will cause a leak.
You can also explicitly call a "copy" method or a "retain" method on a string. In either case, the new string will have a retain count of 1 and will not be autoreleased, so you will need to call the release method on it before you assign a new value.
NSString *dString = [cString retain];
NSString *eString = [cString copy];
...
[dString release];
[eString release];
If it is a property, and you use self.variableName, this will be taken care of for you (through the getters and setters which are generated with #synthesize). If you do it explicitly, you must make sure to call release on variables that you have called retain or copy on.
Edit: As some commentators below have noted, thinking about management in terms of "ownership" is usually the preferred of describing these ideas, rather than retain count.
If it's not a property and just declared in code, you need to explicitly retain or copy it, ie
NSString myString = [otherString copy];
or
NSString myString = [otherString retain];
Either way you also need to ensure it's released at somepoint.
If you're not using the property's setter, like self.name = #"foo" or [self setName:#"foo"], but rather assign the variable directly, like name = #"foo", it doesn't matter at all how the property is declared.
You have to understand that the property syntax is just a shortcut for writing accessor methods (-name and -setName: in this case). If you're not calling these methods (implicitly by setting the property), it doesn't matter how they work internally (which is what you specify by retain or copy).
I get an 'EXC_BAD_ACCESS' error when trying to access variable in a function other than the one it was set in
The variable is set in the 'awakeFromNib' function:
//Retrieve Session-ID
sessionID = [self getSessionID];
And accessed in 'searchBtnClick':
NSLog(#"Commening search (%#)",sessionID); // This causes the error
The variable itself is defined in the header:
NSString *sessionID;
Can someone suggest what might be wrong with that?
The part which of getSessionID which returns the value:
NSString *pC = #"";
// Separate Session ID
pC = [initCookie substringFromIndex:10];
pC = [pC substringToIndex:32];
NSLog(#"Got session ID : %#",pC);
return pC;
Your -getSessionID method is returning an autoreleased variable—when you try to access the pointer again later, the string's already been deallocated and so the reference is no longer valid. You need to call -retain on the variable when you first retrieve it, like this:
sessionID = [[self getSessionID] retain];
Then, later, in your class's -dealloc, you need to balance the retain with a release:
[sessionID release];
If getSessionID follows normal Cocoa conventions, it returns an autoreleased object. You need to retain it, or sessionID will become a dangling pointer as soon as the autorelease pool is drained (probably at the end of the event loop).
If you are new to Objective C and Cocoa, you should make sure to read the Apple documentation about the memory model.
I had similar prob, it crashes when you have not allocated any memory. Releasing it like this:
UIImage *lObj_image = [UIImage imageNamed: #"bluebar.png"];
.
.
.
[lObj_image release];
Check in your viewdidload()