SomeObject *temp = [[SomeObject alloc] init]
self.theObject = temp;
[temp release];
Why is it always done that way? Why not
self.theObject = [[SomeObject alloc] init];
If the theObject property is a retaining property, the first way is correct, because it doesn't leak memory. It's also more efficient than the correct way to write the second version, which is this:
self.theObject = [[[SomeObject alloc] init] autorelease];
Whenever you create an object with alloc you're in charge of releasing it somehow, whether by release or autorelease.
The second version leaks the SomeObject instance, since self.theObject will call a setter that, if properly written, retains the object.
You could just do
theObject = [[SomeObject alloc] init];
and some people certainly do. Others prefer to always use accessors though, either for consistence or to avoid bugs if the accessors have side effects (for exmaple, you would be bypassing KVO notification, which could be a problem if it's not part of an init method).
Related
I have an NSTimer that fires once per second.
And every second I have an NSString that needs to be changed.
I've never tried to deal with memory management before so I'm not sure if what I'm doing is right but instruments is saying under "alloc" that the line of code with stringByReplacingOccurrencesOfString has 45MB of "Live Bytes" after about a minute...
(and the live byte count keeps on rising with every second and eventually crashes the app).
I think my issue lies somewhere with the MutableCopy code?
Here is my code:
-(void)myTimer {
if (testedit) {
[testedit release];
[withString1a release];
[forString1a release];
}
testedit = [[NSString alloc] init];
withString1a = [[NSString alloc] init];
forString1a = [[NSString alloc] init];
testedit = [[NSString alloc] initWithFormat:#"example"];
withString1a = [[NSString alloc] initWithFormat:#"e"];//this string gets its values randomly from an array in my real code
forString1a = [[NSString alloc] initWithFormat:#"flk34j"];//this string gets its values randomly from an array in my real code
testedit = [[testedit stringByReplacingOccurrencesOfString:withString1a withString:forString1a] mutableCopy];//memory leak /:
}
You are allocating memory for each object twice. When you alloc the second time and assign it to the same variable, the first piece of alloc'd memory becomes inaccessible and unreleasable.
Then you make a mutableCopy of testedit and assign the copy to the original's variable. Again, you leave a piece of inaccessible memory floating around.
The rule with non-ARC memory management is - for every alloc, new, copy or retain you need to have a corresponding release. You have 6 allocs, one copy, and only 3 releases.
Here are some suggestions.
Remove these duplicated allocations:
testedit = [[NSString alloc] init];
withString1a = [[NSString alloc] init];
forString1a = [[NSString alloc] init];
Presumably testedit, withString1a and forString1a are all iVars. (Please declare your iVars as autosynthesized properties and refer to them as self.testedit ... etc. that will make your code so much clearer to stack overflowers).
Take out all of this:
if (testedit) {
[testedit release];
[withString1a release];
[forString1a release];
}
Assuming these are all iVars, the correct place to release them is in your object's dealloc method
In fact withString1a and forString1a can be local variables, as you get their content from elsewhere:
NSString* withString1a = [[[NSString alloc] initWithFormat:#"e"] autorelease];
NSString* forString1a = [[[NSString alloc] initWithFormat:#"flk34j"] autorelease];
You can autorelease them as you don't need them to hang around after the method has finished.
These lines can also be written:
NSString* withString1a = [NSString stringWithFormat:#"e"];
NSString* forString1a = [NSString stringWithFormat:#"flk34j"];
(-stringWithFormat is a convenience method that returns an autoreleased object)
That leaves us with these two lines.
testedit = [[NSString alloc] initWithFormat:#"example"];
testedit = [[testedit stringByReplacingOccurrencesOfString:withString1a
withString:forString1a] mutableCopy];
It's not clear why you are treating testedit as an immutable string in the first line and a mutable string in the second. You don't need a mutable string here at all, as you are replacing testedit with a new string.
self.testedit = [[NSString alloc] initWithFormat:#"example"];
self.testedit = [[testedit stringByReplacingOccurrencesOfString:withString1a
withString:forString1a] copy];
(you need copy as stringByReplacingOccurrencesOfString:withString: returns an autoreleased object, and here you want to keep hold of it)
THE last piece of the jigsaw is getting rid of your _testedit iVar memory allocation. You do this in the dealloc method of your object:
- (void) dealloc {
[_testEdit release];
[super dealloc];
}
(Note that init, accessor, and dealloc methods are the three places where you should not refer to an iVar using property syntax.)
All good, but really, you should be using ARC! You are _far_more likely to introduce memory bugs this way than if you rely on the compiler to manage memory for you.
I would suggest you to make use of #property here.
In .h file declare the properties as:
#property (nonatomic, retain) NSString *testedit;
#property (nonatomic, retain) NSString *withString1a;
#property (nonatomic, retain) NSString *forString1a; //if required write the #synthesize as well in .m class
You can write your timer method as:
-(void)myTimer {
self.testedit = #"example";
self.withString1a = #"e";//this string gets its values randomly from an array in my real code
self.forString1a = #"flk34j";//this string gets its values randomly from an array in my real code
self.testedit = [self.testedit stringByReplacingOccurrencesOfString:self.withString1a withString:self.forString1a];
}
In dealloc method, you can set all the above properties as nil (self.testedit = nil;) or do a release on them([testedit release];).
If possible, try to switch to ARC, you dont have to worry about the memory management. The problem with your code was that you are using a lot of alloc/init statements without releasing the variable before doing it. This causes it to lose the reference of that variable and you will leak it. You dont need that many allocation statements. For every allocation or retain, there should be a corresponding release/auto-release statement.
If you're using ARC you shouldn't have an issue. If you aren't using ARC you can try adding autorelease:
testedit = [[[testedit stringByReplacingOccurrencesOfString:withString1a withString:forString1a] mutableCopy] autorelease];
You are getting a memory leak because you never de-allocate testedit. Whenever you call alloc, that means you need to deallocate it. This usually just means calling release.
Do something like this instead, then be sure to free up the memory you've allocated:
NSString* newString = [[testedit stringByReplacingOccurrencesOfString:withString1a withString:forString1a] mutableCopy];
#interface Approval : NSObject
{
NSMutableArray *approvalValues;
}
#property (nonatomic,retain) NSMutableArray *approvalValues;
If i do this, do I still need to call `approvalValues = [[NSMutableArray alloc] init] in the init method? I was under the impression that I had to but it is causing a leak. In the dealloc method I am releasing approvalValues
You need to alloc and init approvalValues. The problem seems to be related to the fact that you are over-retaining your object.
Your code probably looks like this:
self.approvalValues = [[NSMutableArray alloc] init];
alloc will return an object with a retainCount of 1, and when using the retain setter it will get bumped to 2. In order to solve it, you might want to autorelease the object before assigning it, making a code that looks like this:
self.approvalValues = [[[NSMutableArray alloc] init] autorelease];
This will end up with an instance variable with a retainCount of only 1, so when you dealloc the object it won't leak.
Yes you still need to alloc/init, however you only release in dealloc method.
In the init method you will often access the ivar directly and initialize it like this:
approvalValues = [[NSMutableArray alloc] init];
In the dealloc you will need a matchin release like this:
[approvalValues release];
It is often recommended to access the ivars directly in the init and dealloc method to avoid any side effects caused by setters/getters.
Throughout your class you will want to use the KVC setters/getters or dot notation to set objects like this
// Dot notation
NSMutableArray *tmpApprovalValues = [[NSMutableArray alloc] init];
self.approvalValues = tmpApprovalValues;
[tmpApprovalValues release]; tmpApprovalValues = nil;
// Call to setters/getters
NSMutableArray *tmpApprovalValues = [[NSMutableArray alloc] init];
[self setApprovalValues:tmpApprovalValues];
[tmpApprovalValues release]; tmpApprovalValues = nil;
Corrected terminology thanks to #Yuji
Ok, here goes.
Being a Java developer I'm still struggling with the memory management in ObjectiveC. I have all the basics covered, but once in a while I encounter a challenge.
What I want to do is something which in Java would look like this:
MyObject myObject = new MyObject(new MyParameterObject());
The constructor of MyObject class takes a parameter of type MyParameterObject which I initiate on-the-fly.
In ObjectiveC I tried to do this using following code:
MyObject *myObject = [[MyObject alloc] init:[[MyParameterObject alloc] init]];
However, running the Build and Analyze tool this gives me a "Potential leak of an object" warning for the MyParameter object which indeed occurs when I test it using Instruments. I do understand why this happens since I am taking ownership of the object with the alloc method and not relinquishing it, I just don't know the correct way of doing it.
I tried using
MyObject *myObject = [[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]];
but then the Analyze tool told me that "Object sent -autorelease too many times".
I could solve the issue by modifying the init method of MyParameterObject to say return [self autorelease]; in stead of just return self;. Analyze still warnes about a potential leak, but it doesn't actually occur. However I believe that this approach violates the convention for managing memory in ObjectiveC and I really want to do it the right way.
Thanx in advance.
Ok, here's a suggestion.
MyParameter *param = [[MyParam alloc] init];
MyObject *obj = [[MyObject alloc] initWithParam:param]; // do you know if param is retain'd or not?
[param release];
Why do it this way? This is the pattern used throughout ObjC/Cocoa. You add objects to NSArrays this way:
MyThing *thing = [[MyThing alloc] init];
[myMutableArray addObject: thing]; // this calls [thing retain]
[thing release];
You may also want to try to do this:
MyObject *obj = [[MyObject alloc] initWithParam: [MyParameter parameter]];
where:
+ (id) parameter
{
return [[[self alloc] init] autorelease];
}
that way you don't have to worry about it. This is the same as
[NSData data];
[NSArray array];
I hope that helps. Generally, it isn't a good idea to use init during another method call (like a setter or another init). Hiding it behind a Class Method (+ (id) parameter) means the user knows it'll be autorelease'd.
If you're ever unclear about how many retain's or release's something has, you can always do something like this:
[EDIT]
Caveat: Apparently you should never use -retainCount. I find it useful for teaching learners the basics of retain'd Memory Management, but the point is well taken.
Never Use it in actual code or for performance testing. This is only used to learn what retain does (and I believe it functions properly in this case). It will never give you an intelligent answer for an object which is autorelease'd or further retain'd by a NSArray or Other Foundation/AppKit/UIKit Classes
MyParameter *param = [[MyParam alloc] init];
NSLog(#"param retain count: %d",[param retainCount]); // should be 1
MyObject *obj = [[MyObject alloc] initWithParam:param];
NSLog(#"param retain count: %d",[param retainCount]); // should be 2, if MyObject retains it.
[param release];
NSLog(#"param retain count: %d",[param retainCount]); // should be 1
Also, when you dealloc MyObject, you'll need to release param if you retain'd it during initialization.
The following guide put out by Apple should help you to understand Objective-C Memory Management a little better.
MyThing *thing = [[MyThing alloc] init];
[otherThing methodWithAThing:thing];
[thing release];
or:
[otherThing methodWithAThing:[[[MyThing alloc] init] autorelease]];
or (if there is a "convenience constructor" on the class you're using):
[otherThing methodWithAThing:[MyThing thing]];
MyObject *myObject = [[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]];
should be ok, if there is no release in the init (there should definitely not be a release in the init). I often make a class method which makes a autoreleased object. So the code would be:
// using it:
MyObject *myObject = [[MyObject alloc] init:[MyParameterObject defaultParameters];
// in the class implementation of MyParameterObject
+ (MyParameterObject*) defaultParameters{
MyParameterObject* out = [[MyParameterObject alloc] init];
// set some values
return [out autorelease];
}
[[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]]
Without knowing what's going on in the init method, this seems fine.
NB, though, that it's more Objective-Cish to spell this "initWithParameterObject:". Though they gag people new to the language, Obj-C's descriptive method names are actually really helpful for code readability.
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'm working on an app and I'd like to make sure that I'm managing memory properly and releasing everything that I should. In my viewDidLoad method I allocate some variables in determining which background to apply to the view (for internationalization) and the app works fine if I don't release them.
The problem is that if I release the variables the app will crash. Code from viewDidLoad is below:
// Set the background image based on the phone's preferred language
NSString *language = [[NSLocale preferredLanguages] objectAtIndex:0];
NSString *backgroundImageName = [[NSString alloc] init];
backgroundImageName = [NSString stringWithFormat:#"background-%#.png",language];
self.view.backgroundColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:backgroundImageName]];
... do some more initialization stuff ...
// IF THE FOLLOWING ARE RELEASED THE APP WILL CRASH!!!
//[backgroundImageName release];
//[language release];
Why would releasing the backgroundImageName and language variables cause the app to crash?
NSString *language = [[NSLocale preferredLanguages] objectAtIndex:0];
Here, language does not need to be released because objectAtIndex: autoreleases it for you. By convention, you own an object if you've alloced, newed, or copyed it, otherwise you don't.
self.view.backgroundColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:backgroundImageName]];
Here, the UIColor object does need to be released (because you alloced it).
NSString *backgroundImageName = [[NSString alloc] init];
backgroundImageName = [NSString stringWithFormat:#"background-%#.png",language];
Here the string returned by [[NSString alloc] init] does need to be released (because you've alloced it). However, the next line changes backgroundImageName to point to that a new autoreleased string, losing the last reference to the original string without releasing it (a memory leak). backgroundImageName should not be released because it is already autoreleased.
You can avoid the leaks by releasing the UIColor and eliminating the unused string. For example:
NSString *backgroundImageName = [NSString stringWithFormat:#"background-%#.png",language];
... and ...
UIColor* backgroundColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:backgroundImageName]];
self.view.backgroundColor = backgroundColor;
[backgroundColor release];
short answer :
when you create an object using constructors that dont have the word init then you are not responsible for releasing it
see this for more explanation
also the memory management guide is an excellent resource to know more about memory management in objective c
You're not creating the language string; you're just getting back a reference. Only methods that have "new", "copy", or "alloc" in them (by convention) return non-autoreleased objects. For all other methods, it's assumed that you'll discard the variable, so if you want to keep it around, you MUST retain it. The flip side of this is: you should not release these returned objects unless YOU retained them.
The other problem in this code is that backgroundImageName is being assigned twice. The first initialization is being lost. Get rid of it, and just keep the second one, and get rid of both -release calls, they're not needed.