I'm using the following method in my code:
- (NSMutableArray *) newOrderedArray:(NSMutableArray *)array ByKey:(NSString *)key ascending:(BOOL)ascending {
NSSortDescriptor *idDescriptor = [[NSSortDescriptor alloc] initWithKey:key ascending:ascending];
NSArray *sortDescriptors = [NSArray arrayWithObject:idDescriptor];
NSArray *orderArray = [array sortedArrayUsingDescriptors:sortDescriptors];
[idDescriptor release];
NSMutableArray *result = [NSMutableArray arrayWithArray:orderArray];
return result;
}
Is this a well-coded convenience method? As I think, it returns an autoreleased NSMutableArray.
This method is called by another one:
- (id) otherMethod {
NSMutableArray *otherResult = [[[NSMutableArray alloc] initWithCapacity:[otherArray count]] autorelease];
// I add some stuff to otherResult and then...
NSMutableArray *result = [dbUtils newOrderedArray:otherResult ByKey:#"objectId" ascending:NO];
return result;
}
This method (otherMethod) is called in some view controller where I want to store returned array and release it when deallocating the view controller. However, when [result retain] is called in this view controller (because I need it to be available and I can't allow it to be deallocated) I receive the following error:
[CFArray release]: message sent to deallocated instance
I've tried to log [result retainCount] just before calling retain and it print "1". I don't understand why an error is thrown when calling retain.
Thank you,
A
I don't see anything technically wrong with the code above--otherMethod should return an autoreleased NSMutableArray. Are you sure you're getting the error when calling retain? It looks more like you might be accidentally be sending release at some point instead of retain.
Stylistically, there's one thing--methods with "new" in the title should always return non-autoreleased objects, so you should either name your method something else (such as orderedArray...) or use [[NSMutableArray alloc] initWithArray:] instead of arrayWithArray. Also, method signatures shouldn't start with a capital (so ByKey should be byKey.
try this:
NSMutableArray *otherResult = [[NSMutableArray initWithCapacity:[otherArray count]];
Because initWithCapacity will return an autoreleased Array. Right now you tell the Autoreleasepool to release the Array twice.
initWithCapacity:does not return an autoreleased object. – Wevah
AFAIK initWithCapacity is a convenience initializier, which by convention return autoreleased objects. So if the object is only used within a local method, the autoreleasepool should deallocate it. Care to elaborate?
Related
In my iOS app, I am using a NSMutableArray, named imageMArray. I have set its getter and setter properties and instantiated it.
In viewDidLoad:
imageMArray=[[NSMutableArray alloc] initWithArray:CategoryImages];
imageMArray=[self shuffleOnlyArray:imageMArray];
In ShuffleOnlyArray Method:
NSMutableArray *destArray1 = [[NSMutableArray alloc] initWithCapacity: [sourceArray count]] ;
return destArray1;
In shuffle Method:
imageMArray=[[self shuffleOnlyArray:imageMArray] retain];
There appears to be a memory leak in the Shuffle method.
Should I release imageMArray or set it to nil? If it should be released, should it be autoreleased?
imageMArray=[[NSMutableArray alloc] initWithArray:CategoryImages];
In the above statement, you have a memoryleak.
Instead you can have like as follows.
imageMArray = [NSMutableArray arrayWithArray:CategoryImages];
In ShuffleOnlyArray Method, return the autoreleased object.
NSMutableArray *destArray1 = [[NSMutableArray alloc] initWithCapacity: [sourceArray count]] ;
return [destArray1 autorelease];
But after you get it, retain (take the ownership) the array object.
imageMArray=[[self shuffleOnlyArray:imageMArray] retain];
Edit
In shuffle method, do as follows:
NSMutableArray *imageMArray1 = [imageMArray mutableCopy];
if( imageMArray )
{
[imageMArray release];
}
imageMArray=[[self shuffleOnlyArray:imageMArray1] retain];
[imageMArray1 release];
Edit 2:
One more solution:
Use the category to shuffle as mentioned in the SO link
No need of creating new and releasing the arrays.
1 You already have a memory leak in the following lines.
imageMArray = [[NSMutableArray alloc] initWithArray:CategoryImages];
imageMArray = [self shuffleOnlyArray:imageMArray];
In the first line you create an object with retain count 1.
Then you say that your imageMArray pointer points to other object. You should release the first object, because you louse the reference to the fist object and you can not release it after you change the reference!
2 You should not use retain because your ShuffleOnlyArray method returns a retained object.
Your factory method should return an autorelease object and the caller of the factory should decide if if will retain it or not.
Hope I was clear enough
How to write right in this situation:
I have some method, that return NSMutableArray*. Because method not started with init, new or alloc, how write in apple memory-management guide, i return autorealese object.
-(NSMutableArray*)someMethod {
NSMutableArray *array = [NSMutableArray alloc] init] autorealese];
//Some code here
return array;
}
And i have some another methods, that call this one:
-(NSMutableArray*)method1 {
NSMutableArray *array = nil;
if(condition){
array = [self someMethod];
}
return array;
}
-(NSMutableArray*)method2 {
NSMutableArray *array = nil;
array = [self method1];
}
Code work.But XCode analyze tool says that in method2 i get object with count 0. So, how to write this code good?
There is nothing wrong with your code, except that the method2 will return the array that is autoreleased. Thus whatever is calling this method should retain the return value.
Creating an autoreleased NSMutableArray and returning it.
-(NSMutableArray*)someMethod {
NSMutableArray *array = [NSMutableArray alloc] init] autorealese];
//Some code here
return array;
}
Method1 uses autorelease NSMutableArray from someMethod and for the life of Method1 the array will not be autoreleased. That's one of the rules of memory management in objective-c that object lives through the method cycle.
-(NSMutableArray*)method1 {
NSMutableArray *array = nil;
if(condition){
array = [self someMethod];
}
return array;
}
Method2 uses still waiting to be autoreleased NSMutableArray from method1. It's important to notice that b/c you have a condition in method2 the array might be nil.
-(NSMutableArray*)method2 {
NSMutableArray *array = nil;
array = [self method1];
}
So in another words, you are passing autoreleased object along your methods. There is nothing wrong with this. You just have to remember that if you want to store the value of method2 you need to retain it, or it will get autoreleased.
Because of your condition in method1 the analyzer will complain b/c it's not guaranteed that the method1 will return an object, there is a possibility it will return nil.
I was running Leaks tool and discovered a massive leak in my Dictionary mutableDeepCopy but I can't figure out what's wrong with the code. Any suggestions?
#interface RootViewController : UIViewController{
NSDictionary *immutableDictionary;
NSMutableDictionary *mutableDictionary;
}
Here is the line of code that's highlighted in Instruments
self.mutableDictionary = [self.immutableDictionary mutableDeepCopy];
Here is the method for creating a mutable copy of a Dictionary
#interface NSDictionary(MutableDeepCopy)
-(NSMutableDictionary *)mutableDeepCopy;
#end
Here is method implementation, I've highlighted the code that Leaks saids is leaking 100%
- (NSMutableDictionary *) mutableDeepCopy {
NSMutableDictionary *dictionaryToReturn = [NSMutableDictionary dictionaryWithCapacity:[self count]];
NSArray *keys = [self allKeys];
for(id key in keys) {
id value = [self valueForKey:key];
id copy = nil;
if ([value respondsToSelector:#selector(mutableDeepCopy)]) {
copy = [value mutableDeepCopy];
} else if ([value respondsToSelector:#selector(mutableCopy)]) {
copy = [value mutableCopy]; //This is the Leak
}
if (copy == nil) {
copy = [value copy];
}
[dictionaryToReturn setValue:copy forKey:key];
}
return dictionaryToReturn;
}
You need to analyse this in light of Apple's Memory Management Rules.
Starting with this line:
self.mutableDictionary = [self.immutableDictionary mutableDeepCopy];
I would expect mutableDeepCopy to return an object I own, so at some point I need to release or autorelease it. e.g.
NSMutableDeepCopy* temp = [self.immutableDictionary mutableDeepCopy];
self.mutableDictionary = temp;
[temp release];
or
self.mutableDictionary = [[self.immutableDictionary mutableDeepCopy] autorelease];
So now we need to look at mutableDeepCopy. Because it has 'copy' in the name it needs to returned an "owned" object which, in practice means "forgetting" to release the returned object. You have already failed to do that when you create the returned object in the first line, since dictionaryWithCapacity: gives you an object you do not own. Replace it with
NSMutableDictionary *dictionaryToReturn = [[NSMutableDictionary alloc] initWithCapacity:[self count]];
Now you own it.
It is important that you make your mutableDeepCopy obey the rules because it means you can treat the objects returned from mutableDeepCopy, mutableCopy and copy in exactly the same way. In all three cases you own the object copy that you insert into the array. Because you own it, you must release it or it'll leak as you found out. So, at the end of the loop, you need
[copy release];
That'll stop the leak.
How is your property declared? If is is retain or copy, then this doesn't leak.
Your problem is that the name mutableDeepCopy suggests that it returns a retained object, and not an autoreleased one as it actually does.
Edit:
And at the mutableDeepCopy itself, you need to release the copy variable after adding to the dictionary.
mutableCopy increments the retain count of the object, as does setValue:forKey:. This means that when dictionaryToReturn is dealloc'ed, the object that had mutableCopy called still has a retain count of one.
Try doing this instead:
copy = [[value mutableCopy] autorelease];
I have a memory leak when i call a method that return me a string----
the method definition is as follows
-(NSMutableArray *)read
{
NSMutableArray *dataArray = [[NSMutableArray alloc] init];
//picking data from database here
return dataArray;
}
this show a big memory leak
i also tried--- NSMutableArray *dataArray = [[[NSMutableArray alloc] init]autorelease];
but this time leack checking process gets hanged
i also cannot release that array before return
please help
-(NSMutableArray *)read
{
NSMutableArray *dataArray = [[NSMutableArray alloc] init];
//picking data from database here
return dataArray;
}
Anything that uses the method read will expect to get back an object it does not own. However, as written here, dataArray is still owned at the point of return. You can't release it because that might make it go away altogether. You must, in this instance autorelease the array. You can either do this:
-(NSMutableArray *)read
{
NSMutableArray *dataArray = [[[NSMutableArray alloc] init] autorelease];
//picking data from database here
return dataArray;
}
or this
-(NSMutableArray *)read
{
NSMutableArray *dataArray = [[NSMutableArray alloc] init];
//picking data from database here
return [dataArray autorelease];
}
You say "leak checking process get hanged" but I'm really not sure what you mean by that. Whether it hangs, crashes or plays the Botswana National Anthem, you definitely need to autorelease the returned array and any other problem is actually a different problem. Possibly, you are forgetting to retain the data elsewhere.
Another answer more...
There are many conventions in cocoa/cocoa-touch, there is one of them that says that if a method has the prefix init then you will have the ownership of that object (hence you have to release it)
This is NOT your case, hence if you do:
DatabaseReader *dbReader = [[DatabaseReader alloc] init];
NSMutableArray *mutArray = [dbReader read];
[dbReader release];
you are NOT supposed to release mutArray. BUT, the object created HAS to be released by someone. So you can do as JeremyP wrote. alloc/init and put it into a autorelease pool inside read method implementation. Or, you can do:
-(NSMutableArray *)read
{
NSMutableArray *dataArray = [NSMutableArray array];
//IMPORTANT:
//Did you noticed that I am not using any method
//with init prefix for the creation of dataArray ?
//so I don't need to release by my self ;)
//picking data from database here
return dataArray;
}
Which is basically the same. ;)
Ownership of the returned object may be returned to the object that receives from this function. You may do some debugging with the object's retain count using something like this...
NSLog(#"Retain count: %i", [dataArray retainCount]);
Turn on the debugging console (Command + R in Xcode) to see the NSLog output.
I have a NSMutableDictionary with the key being the first alphabet of the name of an object. The view is something like the 'Contacts' tab on iphone. Additionally user can select individual objects in the list.
In the code I find each selected object to process them further.
NSMutableArray *objectsToAdd = [[NSMutableArray alloc] init];
NSMutableArray *array = nil;
for (NSString *key in self.nameIndex) {
array = (NSMutableArray *)[searchedNameDictionary valueForKey:key];
for (Objects *eachObject in array) {
if (eachObject.objectIsSelected){
[objectsToAdd addObject:eachObject];
}
}
}
[array release];
-(void)dealloc()
{
[searchedNameDictionary release];
}
The app is crashing where I release searchedNameDictionary, with the message that the deallocated object is being referenced.
Now if in the code above, I remove [array release] the app works fine.
My question is does releasing 'array' is actually releasing the objects in searchedNameDictionary, which is what seems to be happening.
Would not releasing array cause memory leak?
You shouldn't release returned object unless they come from an alloc or copy method.
Returned objects are autoreleased otherwise, if you want to keep it around your should retain it right after receiving it.
array = (NSMutableArray *)[searchedNameDictionary valueForKey:key];
This returns an autoreleased object, thus you don't need to release it.
There are some other...issues with your code too, but mostly style things. Get rid of the [array release] and you're good to go as far as that issue is concerned.