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.
Related
I have an NSMutableArray with the following property:
#property (nonatomic, strong) NSMutableArray *alarmTableArray;
alarmTableArray = [[NSMutableArray alloc]init];
FMDBDatabaseAccess *db = [[FMDBDatabaseAccess alloc] init];
alarmTableArray = [db getAlarm];
I tried releasing this array but I end up with EXC_BAD_ACCESS.
I am really worried about this.
How to release this array?
You're using the descriptor of "strong" which is an ARC term. This should be retain and if you just set the property to nil it will release it automatically. You should set it to nil in your viewDidUnload since your ViewWillDissappear only means your viewcontroller is leaving visibility and not that it is being destroyed.
Updated Answer
I think I know what you're trying to do. You want grab an array of rows from your SQL and store it in one of your array.
One of the techniques for getting rows of data from SQL and storing into a class instance variable array is to NOT return a temporary array but pass the class instance variable array as a reference into your method and modify the array directly.
So instead of this pseudo-code
-(NSMutableArray *)doSomething
{
NSMutableArray *tempArray;
while (DB select statement has found rows)
{
CockTail *objCT = [[CockTail alloc] init];
objCT.name = #"...";
objCT.price = #"...";
[tempArray addObject:objCT];
[objCT release];
}
return [tempArray autorelease];
}
// class instance variable array
instanceVarArray = [[NSMutableArray alloc] init];
instanceVarArray = [self doSomething]; // here is where you confusion arise
You can do it this way:
-(void)doSomething:(NSMutableArray *)paramArray
{
// remove previously fetched data
[paramArray removeAllObjects];
SQL select statement
while(has rows)
{
CockTail *objCT = [[CockTail alloc] init];
objCT.name = #"...";
objCT.price = #"...";
// NOTE: we are directly modifying our class instance variable array
// here since it was passed by reference :D
// and so there is no need to worry about releasing the array
[paramArray addObject:objCT];
[objCT release];
}
}
// Now all you do is pass in your class instance variable array
instanceVarArray = [[NSMutableArray alloc] init];
[self doSomething:instanceVarArray];
Original Answer
Um, maybe I am wrong but aren't you essentially throwing away that "alloc init" on the first line here when you assign the array something from your FMDBDatabaseAccess:
// LINE 1: this instance of NSMutableArray here is allocated
alarmTableArray = [[NSMutableArray alloc]init];
// LINE 2
FMDBDatabaseAccess *db = [[FMDBDatabaseAccess alloc] init];
// LINE 3:this line here essential breaks the pointer link point to the NSMutableArray instance on line 1
alarmTableArray = [db getAlarm];
Now unless you do
// LINE 4
[alarmTableArray retain];
Otherwise, your alarmTableArray was never allocated (since you overwrote the pointer link). And as a result, you've caused a memory leak as your profiler told you.
Doing a release now would give your that EXEC_BAD_ACCESS
What I think you want to do is this:
alarmTableArray = [[NSMutableArray alloc]init];
FMDBDatabaseAccess *db = [[FMDBDatabaseAccess alloc] init];
// this now uses the setter method (mutator method generated by #property) to do the copy
self.alarmTableArray = [db getAlarm];
Looking at your while loop, I have to ask why are you releasing a local scope variable?
CockTail *cocktailValues = [[CockTail alloc] init];
...
[cocktails addObject:cocktailValues];
[cocktailValues release];
Breakdown of each line of code above:
When you alloc and init the CockTail object the release/retain count is 0.
Adding the object to the NSMutableArray increases the release/retain count to 1.
Releasing the CockTail object after you added it to array reduce the release/retain count back down to 0.
Therefore, later when you release the NSMutableArray or try to access an object in it, the objects are already gone.
Remember the number one rule, only release what you retain.
I have been pulling out my hair trying to figure out why this is leaking. In my .h file I have a synthesized property nonatomic, retained NSMutableArray. In my viewDidLoad I declare it as:
self.tableData = [[NSMutableArray alloc] init];
[self.tableData removeAllObjects];
fillData(self.tableData);
Throughout my application, I call [self.tableData removeAllObjects] and then repopulate it with the fillData(self.tableData) function. This function fills up the data from a static C++ string set:
void fillData(NSMutableArray* list)
{
for (set<string>::const_iterator itr = sortedData.begin(); itr != sortedData.end(); ++itr){
[list addObject:[NSString stringWithFormat:#"%s", ((string)*itr).c_str()]];
}
}
In my dealloc method I do:
[self.tableData removeAllObjects], [self.tableData release], tableData = nil;
Where did I drop the ball? Instruments says it's in the [list addObject....] line.
Thanks
self.tableData = [[NSMutableArray alloc] init];
[self.tableData removeAllObjects];
fillData(self.tableData);
+1 retain for alloc, +1 retain for using the property's setter. You haven't balanced the +1 from alloc. If you are going to use the setter:
self.tableData = [NSMutableArray array];
fillData(self.tableData);
Note that removeAllObjects in that is completely pointless.
This is odd, too:
[self.tableData removeAllObjects], [self.tableData release], tableData = nil;
First, don't bother removing the objects. When the array is deallocated, it'll release all objects. Secondly, using the setter to call release and then immediately do a direct assignment is inconsistent. Either do:
self.tableData = nil;
Or:
[tableData release], tableData = nil;
(Note that the use of the , in all of this is also purely for your benefit -- it has no impact on generated code.)
Also, use stringWithUTF8String: and not stringWithFormat:.
Not sure if it's the leak, but this looks like it's a problem:
self.tableData = [[NSMutableArray alloc] init];
You say that tableData is a property that's retained. Try:
self.tableData = [NSMutableArray arrayWithCapacity:10];
That way the property retains it and the array itself is autoreleased. Your release in dealloc will bring the retain count back down to zero.
The problem is that your property is set as retain, and you set it to an already retained object.
You should do it like this:
// viewDidLoad
NSMutableArray *array = [[NSMutableArray alloc] init];
self.tableData = array;
[array release]; // this is important
// dealloc
self.tableData = nil; // will automatically release the array
In your dealloc, you use properties which retain the tableData again. That is not really what you want, so do:
[tableData release];
or
[self->tableData release]; // not necessary, but some prefer it.
or
self.tableData = nil; // property will handle release
No need to clear the tableData, no need to set anything to nil (you are deallocating, so nothing will access it anymore).
I am developing an iphone app. Instruments reported a leaked object ServiceTypes. Below is the relevant code. Does anyone have any ideas? Thanks a lot for your help.
ServiceTypes *serviceTypes = [[ServiceTypes alloc] init];
if ([userConnection getServiceTypes:serviceTypes]) {
if ([serviceTypes.types length] > 0) {
NSArray *array = [[NSArray alloc] initWithArray:[serviceTypes.types componentsSeparatedByString: SERVICE_TYPE_DELIMITOR]];
serviceRequestTypes = [[NSMutableArray alloc] initWithArray:array];
[array release];
}
}
[[self typesTableView] reloadData];
[serviceTypes release];
It doesn't look like serviceTypes is being leaked. From the code you posted, serviceTypes is always released at the end of the method, and it doesn't appear to be retained anywhere in your sample. My question is: what happens inside getServiceTypes:. Does that method retain the serviceTypes parameter?
One more thing. If serviceRequestTypes is an instance variable (and it looks like it is), then you may be leaking memory by reassigning it without releasing the existing serviceRequestTypes object first. You should either rewrite serviceRequestTypes to be a property and use a synthesized accessor or make sure to release it every time before assigning. If its current value is nil, no big deal; the release message will simply be ignored. For example:
[serviceRequestTypes release];
serviceRequestTypes = [[NSMutableArray alloc] initWithArray:[serviceTypes.types componentsSeparatedByString:SERVICE_TYPE_DELIMITER]];
I started dealing with NSOperations and (as usual with concurrency) I'm observing strange behaviour.
In my class I've got an instance variable:
NSMutableArray *postResultsArray;
when one button in the UI is pressed I initialize the array:
postResultsArray = [NSMutableArray array];
and setup the operations (together with dependencies).
In the operations I create a custom object and try to add to the array:
PostResult *result = [[PostResult alloc] initWithServiceName:#"Sth" andResult:someResult];
[self.postResultsArray addObject:result];
and while adding I get:
-[CFArray retain]: message sent to deallocated instance 0x3b40c30
which is strange as I don't release the array anywhere in my code (I did, but when the problem started to appear I commented all the release operations to be sure that they are not the case). I also used to have #synchronized section like below:
PostResult *result = [[PostResult alloc] initWithServiceName:#"Sth" andResult:someResult];
#synchronized (self.postResultsArray) {
[self.postResultsArray addObject:result];
}
but the problem was the same (however, the error was for the synchronized operation).
Any ideas what I may be doing wrong?
postResultsArray = [NSMutableArray array];
[NSMutableArray array] is a convient method which is equivalent to [[[NSMutableArray alloc] init] autorelease]. So there is an implicit (auto)release there. Since you're going to keep it, you have to use one of these 3 changes:
postResultsArray = [[NSMutableArray array] retain];
postResultsArray = [[NSMutableArray alloc] init];
Exploit the fact that a setter should retain the new value (if you declare as #property(retain)):
self.postResultsArray = [NSMutableArray array];
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?