I'm beginning to get my head round all the memory management stuff, but I'm a bit puzzled by the use of properties with arrays. If I declare the property in the interface like so -
#property (nonatomic,retain) NSMutableArray *myArray;
then synthesize it in the implementation, do I need to alloc it when I create the array? Like so -
self.myArray = [[NSMutableArray alloc] init];
or does this result in an extra retain count? Should I just do -
self.myArray = [NSMutableArray array];
and let the setter do the retaining?
Many thanks to anyone who can clarify this for me!
In both cases you are letting the setter retain your instance.
In this case you are overretaining:
self.myArray = [[NSMutableArray alloc] init];
The setter does and the alloc message sent.
This can be fixed with:
self.myArray = [[[NSMutableArray alloc] init] autorelease];
or
NSMutableArray *newInstance = [[NSMutableArray alloc] init];
self.myArray = newInstance;
[newInstance release];
This is fine
self.myArray = [NSMutableArray array];
however not every class has a convenience class method to return an autoreleased instance.
Have a look at the Memory Management Programming Guide / Object Ownership and Disposal, this will give you a good understanding about when the retain counts increases and when you should release.
Related
I always have error when working with arrays (non ARC code).
My code:
#implementation InfoController
NSMutableArray *lbCityArray;
NSMutableArray *lbTimeArray;
NSMutableArray *lbCameInArray;
NSMutableArray *lbCameOutArray;
NSMutableArray *lbInArray;
NSMutableArray *lbOutArray;
in ViewDidLoad I do something
- (void)viewDidLoad
{
[super viewDidLoad];
lbCityArray = [[NSMutableArray alloc] initWithCapacity:1];
lbTimeArray = [[NSMutableArray alloc] initWithCapacity:1];
lbCameInArray = [[NSMutableArray alloc] initWithCapacity:1];
lbCameOutArray = [[NSMutableArray alloc] initWithCapacity:1];
lbInArray = [[NSMutableArray alloc] initWithCapacity:1];
lbOutArray = [[NSMutableArray alloc] initWithCapacity:1];
//—add some values to arrays
NSString *City = #"London";
[lbCityArray addObject:City];
//—————————————-----------------------//
}
and always when I click Back button app crash with EXC_BAD_ACCESS. If I comment adding values to array all work, Back button don't crash app. I read if you use non ARC code you must manually release in dealloc.
I add to dealloc
[_InfoTableView release];
[lbCityArray release];
[lbTimeArray release];
[lbCameInArray release];
[lbCameOutArray release];
[lbInArray release];
[lbOutArray release];
[super dealloc];
and nothing changes, app still crash. Where can be problem ?
Solution - I move to ARC and all problems gone. Thanks.
It would help a lot if you made your variables into instance variables instead of global variables.
Change this:
#implementation InfoController
NSMutableArray *lbCityArray;
NSMutableArray *lbTimeArray;
NSMutableArray *lbCameInArray;
NSMutableArray *lbCameOutArray;
NSMutableArray *lbInArray;
NSMutableArray *lbOutArray;
into:
#implementation InfoController {
NSMutableArray *lbCityArray;
NSMutableArray *lbTimeArray;
NSMutableArray *lbCameInArray;
NSMutableArray *lbCameOutArray;
NSMutableArray *lbInArray;
NSMutableArray *lbOutArray;
}
Without the curly braces you are actually creating global variables, not instance variables.
I don't understand where is the leak here.
I am querying for a field in the database. After this, I am inserting in a NSMutableArray list.
#property (nonatomic, retain) NSMutableArray *bList;
#property (nonatomic, retain) NSString *icon;//Model
Model *newModel = [[Model alloc] init];
newModel.icon = [NSString stringWithUTF8String:(char *) sqlite3_column_text(compiledStatement, 2)];
[self.bList addObject:newModel];
[newModel release];
And in the end:
- (void)dealloc {
[self.bList release];
[super dealloc];
}
[self.bList release];
Don't do that; either use self.bList = nil; or [bList release], bList = nil;
There doesn't appear to be a leak in that code, unless I'm missing something obvious.
Remember that leaks identifies where the leak was allocated, not where it was leaked. The leak is likely caused by an over-retain elsewhere.
Based on your comment on #murat's answer, If you are doing,
self.blist = [[NSMutableArray alloc] init];
then you are leaking memory as you are taking ownership twice in that line. One by alloc-init and one based on the property (assuming it is retained, mostly should be). In such case releasing it once in dealloc won't balance the retain-release calls. You will have to rather do,
self.blist = [NSMutableArray array];
or
self.blist = [NSMutableArray arrayWithCapacity:100];
You create an instance of array but did not take a memory space for it. For your blist array, allocate a memory space.
self.blist= [[NSMutableArray alloc]init]; // or you can create like
self.blist= [[NSMutableArray alloc]initWithCapacity:100];
I just ran my app through the Leaks in Instruments and I am being told that the following code causes leaks, but I don't see how.
I allocate some NSMutableArrays in my viewDidLoad with this code:
- (void)viewDidLoad {
[super viewDidLoad];
self.currentCars = [[NSMutableArray alloc] init];
self.expiredCars = [[NSMutableArray alloc] init];
}
Then I populate these arrays inside of my viewWillAppear method with the following:
[self.currentCars removeAllObjects];
[self.expiredCars removeAllObjects];
for (Car *car in [self.dealership cars]) {
if ([car isCurrent])
[self.currentCars addObject:car];
if ([car isExpired])
[self.expiredCars addObject:car];
}
And later in the code I release these arrays here:
- (void) viewWillDisappear:(BOOL)animated {
if (currentCars != nil) {
[currentCars release], currentCars = nil;
}
if (expiredCars != nil) {
[expiredCars release], expiredCars = nil;
}
[super viewWillDisappear:animated];
}
Any ideas? Thanks!
Your leak is here:
self.currentCars = [[NSMutableArray alloc] init];
self.expiredCars = [[NSMutableArray alloc] init];
Assuming that you declared property accessores like this:
#property(nonatomic, retain) NSMutableArray *currentCars;
#property(nonatomic, retain) NSMutableArray *expiredCars;
In my opinion, the best way to find leaks (other than using Instruments) is to keep track of the retain count manually.
If you were to do that with for example currentCars, you would find your leak easily. Here is what happens:
self.currentCars = [[NSMutableArray alloc] init];
// The 'init' makes the retain count 1.
// 'self.currentCars = ..' translates to the setCurrentCars: method.
// You probably did not implement that method yourself,
// but by synthesizing your property it is automatically implemented like this:
- (void)setCurrentCars:(NSMutableArray *)array {
[array retain]; // Makes the retain count 2
[currentCars release];
currentCars = array;
}
// In your viewWillDisappear: method
[currentCars release], currentCars = nil; // Makes the retain count 1 so the object is leaked.
The solution is simple. Use this:
NSMutableArray *tempMutableArray = [[NSMutableArray alloc] init];
self.currentCars = tempMutableArray;
[tempMutableArray release];
A little sidenote. You shouldn't release your objects in viewWillDisappear:. The recommended place to do that is dealloc. So your code would be:
- (void)dealloc {
[currentCars release], currentCars = nil;
[expiredCars release], expiredCars = nil;
[super dealloc];
}
The problem is (probably) that you are using the property accessors for the initial setting of the arrays in -viewDidLoad. Since well-implemented property accessors will retain the object, you are getting 1 retain from the +alloc and another retain from assigning it. To fix this, you should release your arrays after assigning them or use [NSMutableArray array] to get an autoreleased one to use for your initial assignments.
Unless you're doing something very odd in currentCars, expiredCars, dealership or cars, no, there's no leak there.
Instruments' pointer to the location of a leak isn't necessarily where the object is actually leaked, per se. If I were to guess, I'd say you're probably neglecting to release either currentCars or expiredCars in your dealloc method.
Does the release, recursively releases all inner objects? or must it be done manualy?
Can I do just this?
NSMutableArray *list = [[NSArray alloc] init];
// ...
// fill list with elements
//...
[list release];
Or must I release all inner objects one by one before releasing the NSMutableArray? // Suposing there isn't any other reference to the contained objects, except on the list itself.
Yes it does. It retains them when added, and releases them when dealloc'd. This is actually one of the most common questions I see here.
If you are owning the object then you will have to release it.
NSMutableArray *list = [[NSArray alloc] init];
NSString *str = [[NSString alloc] init] // you are the owner of this object
[list addObject:str];
[str release]; // release the object after using it
[list release];
If you are not the owner of the object then you should not release.
NSMutableArray *list = [[NSArray alloc] init];
NSString *str = [NSString string]; // you are not owning this object
[list addObject:str]; // str retain count is incremented
[list release]; // str retain count is decremented.
This is the concept which even array also uses. When you add any object to the array, array will retain it. In the sense it becomes the owner of that object and It will release that object when you release the array.
With an instance variable myArray:
#interface AppController : NSObject
{
NSArray *myArray;
}
Sometimes I see myArray initialized like this:
- (void)init
{
[super init];
self.myArray = [[NSArray alloc] init];
return self;
}
and sometimes I see it with a more complicated method:
- (void)init
{
[super init];
NSArray *myTempArray = [[NSArray alloc] init];
self.myArray = myTempArray
[myTempArray release];
return self;
}
I know that there's no difference in the end result, but why do people bother to do the longer version?
My feeling is that the longer version is better if the instance variable is set up with a #property and #synthesize (possibly because the variable has already been alloced). Is this part of the reason?
Thanks.
If myArray is a property and it's set to retain or copy (as it should be for a property like this), then you'll end up double-retaining the variable when you do this:
self.myArray = [[NSArray alloc] init];
The alloc call sets the reference count to 1, and the property assignment will retain or copy it. (For an immutable object, a copy is most often just a call to retain; there's no need to copy an object that can't change its value) So after the assignment, the object has retain count 2, even though you're only holding one reference to it. This will leak memory.
I would expect to see either a direct assignment to the instance variable
myArray = [[NSArray alloc] init];
Or proper handling of the retain count:
NSArray *newArray = [[NSArray alloc] init];
self.myArray = newArray;
[newArray release];
Or the use of autoreleased objects:
self.myArray = [[[NSArray alloc] init] autorelease]; // Will be released once later
self.myArray = [NSArray array]; // Convenience constructors return autoreleased objects
This is an idiom used in mutators (sometimes called "setters"), but I think you typed it slightly wrong. Usually it looks like this:
-(void)setMyName:(NSString *)newName
{
[newName retain];
[myName release];
myName = newName;
}
The new name is retained, since this instance will need to keep it around; the old name is released; and finally the instance variable is assigned to point to the new name.
I have a feeling you mean this:
NSArray* a = [NSArray arrayWithObjects:#"foo", #"bar", nil];
and this
NSArray* a = [[NSArray alloc] initWithObjects:#"foo", #"bar", nil];
//...
[a release];
With the first style, the static method performs an alloc/init/autorelease on it for you so you don't have to. With the second style, you have more control over when the memory is released instead of automatically releasing when you exit the current block.
That code will crash your application. The second version only copies the pointer then releases the instance. You need to call [object retain] before releasing the reference.