I have property like this:
#property(nonatomic,retain) NSString *porpertyList;
#synthesize porpertyList = _porpertyList;
- (void)dealloc
{
[_porpertyList release];
}
And if i do this _porpertyList = #""; in my app. Property is released ?
//Edited
Now i don't understand when i should use this #synthesize porpertyList = _porpertyList; ?
Depends on what memory model you are using. If you are using ARC, there's no need to write a dealloc to release retained properties, this is done for you. If you are not using ARC, you want to release the variables for the retained properties:
- (void) dealloc {
[_propertyList release];
[super dealloc];
}
Two things to note here:
You want to release the variable here, not set the property to nil. This avoids side-effects that could occur when using setters (custom behavior, kvo notifications).
Don't forget to call [super dealloc];
If you access property like this
self.property=#"";
you are in fact using setter method( which is auto-created thanks to #synthesize). So, in this case, the old object is released and new one is assigned and retained.
If you synthesized your property using
#synthesize property= _property;
then if you call
_property=#"";
then you just assign new value to the property. Nothing is being released then.
So, in your dealloc method you have some choices:
-(void)dealloc
{
self.property=#"";//old value released, new value is #""
self.property=nil;//old value released, new value is nil
[_property release]; //old value released
[super dealloc];
}
#synthesize porpertyList = _porpertyList;
Whenever you synthesize an property... you up its retain count by 1..so that's why you have release in your dealloc.
Using self.propertyList = something
and
porpertyList = something
are very different things and the latter one should be avoided when using properties..
That is why porpertyList = _porpertyList; is there..so that you don't use propertyList instead of self.porpertyList
The reason is ..that popertyList is a pointer..
when you do self.porperty = something ..you make a separate copy of that object for yourself(not in case of #"")
but if you do popertyList = something .. you make it point to another object thus messing with the whole retain count it had initially which can make your program behave strangely..
if you use the #property option for variable name you should assign to it using the
self.propertyList = #"" rather then _propertyList = #"". using self.propertyList will release any previous memory it was using when u assign to it
_porpertyList = #"" will not release anything. If you want to release, you can use self. porpertyList = nil. This will release it properly.
Related
I'm a little confused about synthesized properties. I have an array that I want to be accessible from other classes so this is my code:
MyClass.h
#interface MyClass : CCLayer {
NSMutableArray *myArray;
}
#property (nonatomic, retain) NSMutableArray *myArray;
MyClass.m
#synthesize myArray;
-(id)init
{
myArray = [[NSMutableArray alloc] init];
}
-(void)dealloc
{
[myArray release];
myArray = nil;
}
I am a little confused now..is myArray the same as self.myArray? Do I have to release self.myArray as well? Thanks.
You declared your property as retain, it means that it will be retained automatically if you will set is using self.myArray. So, you can simply create autoreleased array in your init method and set it as
myArray = [NSMutableArray array];
self.myArray = myArray;
in this case you are not have to release it in the dealloc method or anything else. And as dasblinkenlight said you have to use #synthesize if you want to be sure that self.myArray is linked with your myArray instance.
Assuming that your #synthesize directive looks like this
#synthesize myArray;
you do not need to do anything in addition to what you are already doing: your property stores its value in the instance variable of the same name.
EDITED : Removed the alternative that suggests setting self.myArray in the dealloc method.
Yes you do, the best method is to set the property nil and release your variable.
-(void)dealloc{
self.myArray = nil;
[myArray release];
[super dealloc];
}
The code you provided is not really correct.
No, accessing a property and accessing the field itself are not the same.
My guess is that you are looking at old obj C examples where it was necessary to create the field with the property.
You also have no #synthesize directive in your code.
In current obj C code there is no need to declare a field to back the property, the field and the getter and setter will be autosynthesized (generated by the compiler) for you.
The default field generation is the name of your property with an underscore in front of it.
When you access the field directly via _myArray you will bypass any retain or release code that is contained in the generated getter/setter and have to manually manage memory in a non ARC project.
So to sum up, you dont need your field definition, and you dont need a synthesize directive.
You access your field directly with _myArray, or the property via self.myArray
They are not the same thing, one goes through generated code which obeys your property definition as to retain, assign, copy and accessing the field directly bypasses these semantics altogether.
If you define your property as retain you will need to release it in dealloc
You can use either
self.myArray = nil;
which will handle the release or
[_myArray release];
_myArray = nil;
Although someone in a previous post said setting the property to nil in dealloc might cause a problem Ive never seen it actually happen in my apps, ymmv
To answer your questions:
I am a little confused now..is myArray the same as self.myArray?
Yes, but no. Both point to the same object, the same area in memory. If you read myArray or self.myArray, they're identical in behavior minus the message send overhead for self.myArray.
However if you assign to myArray, the object will not be retained. It will only be retained if you assign to self.myArray.
Do I have to release self.myArray as well?
No.
You can also choose to either release or set the property to nil. As long as the property is #synthesize'd both examples do the same thing:
-(void) dealloc
{
[super dealloc];
[myArray release];
}
-(void) dealloc
{
[super dealloc];
self.myArray = nil;
}
See here for a discussion of the pros/cons to each approach.
From the question I think you're the developer who should really be using ARC. You'll have less to learn and fewer technical problems down the road. I can't understate how important using ARC is in these days, specifically if you don't have much ObjC experience. Read this how to enable ARC for cocos2d or just use Kobold2D to be able to work with an ARC-enabled cocos2d out of the box.
This is one of my method.
- (void)getSearchResultsByKeyword:(NSString *)keyword
searchOptions:(NSArray *)searchOptions
searchGroupsInResult:(NSArray *)searchGroupsInResult
{
_searchKeyword = [keyword retain];
_searchOptions = [searchOptions retain];
_searchGroupsInResult = [searchGroupsInResult retain];
[_searchResultsGroups removeAllObjects];
[_searchResultsGroupsIndexToNameMap removeAllObjects];
_pageNo = 1;
[[NSNotificationCenter defaultCenter] postNotificationOnMainThreadName:SearchResultsRetrievingStartLodingNotification
object:self];
[_dataProvider startGettingSearchResultsByKeyword:self.searchKeyword
searchOptions:_searchOptions
searchGroupsInResult:_searchGroupsInResult
pageNo:_pageNo
delegate:self];
}
In my method I have called retain on the objects which are parameters. So I have owned the object and has increased the retain count. So my problem is, how do I decrease the retain count after the
[_dataProvider startGettingSearchResultsByKeyword:self.searchKeyword
searchOptions:_searchOptions
searchGroupsInResult:_searchGroupsInResult
pageNo:_pageNo
delegate:self];
call. ( [keyword release] or [_searchKeyword release] ) ??
In my header file I have declared the _searchOptions as a private instance and _searchKeyword as a readonly property. In my implementation file, I have released both instances in dealloc.
I ran Analyze tool and it did not show this thing as an issue. But I have a doubt on it.
So, please show me a necessary way to work on this thing.
I'm working on XCode4 and iOS 4.3.
Thanks.
jaydee3's answer is correct. I would add that you really should use #properties with synthesized accessors. Then, instead of setting your instance variables directly, use the accessor methods. That way you can encapsulate all of the memory management of your instance variables in the accessor methods. This has the advantage of being more readable, much less error prone, and makes your code easier to modify in the future.
So, in your .h (or in a class extension in your .m if the properties should be "private"):
#property (nonatomic, copy) NSString *searchKeyword;
In your .m:
- (void)dealloc
{
self.searchKeyword = nil;
[super dealloc];
}
#synthesize searchKeyword = _searchKeyword;
Finally, in your -getSearchResultsByKeyword:searchOptions:searchGroupsInResult: method:
self.searchKeyword = keyword;
instead of
_searchKeyword = [keyword retain];
Now you don't have to worry about releasing or retaining searchKeyword. The setter method generated by the #synthesize directive will take care of it for you. I suggest reading Apple's documentation on Declared Properties.
Since you are assigning to an ivar, you have to retain it. This is correct.
Releasing it within dealloc is also correct. But thats not enough. Two things:
1) It's better to copy strings, rather than retain them. So use _searchKeyword = [keyword copy];. (This is also retained. So the retainCount is 1 after that.)
2) Also there is a problem, when you call your method the second time. That is the point, where you do have a leak. You are assigning a new value to your ivar `_searchKeyword', dismissing the pointer to the old keyword, which is still retained. So before assigning the new one, release the old one also.
Example:
[_searchKeyword release];
_searchKeyword = [keyword copy];
If you copy it, this is good, but if you only retain, it would be even better to do it like that (in case both reference the same object):
[keyword retain];
[_searchKeyword release];
_searchKeyword = keyword;
When there are two objects that are pointers to the same thing, it doesn't matter which one you call release on. The thing pointed at is where the reference count gets decremented.
Given you've released it in one place, and the analyzer isn't complaining, you don't have a problem.
What difference does it make in memory management to define a variable as a property? For instance:
#interface foo {
NSString *theStr;
}
#end
#implementation foo
- (void)bar {
NSLog(theStr);
}
#end
Versus:
#interface foo {
NSString *theStr;
}
#property(retain) NSString *theStr;
#end
#implementation foo
#synthesize theStr;
- (void)bar {
NSLog(theStr);
}
#end
It seems like the first is autoreleased or something similar, while the second is retained throughout the life of the class. Is that the case, or what is the difference?
If you define a variable just in the interface without defining it as a property (as in your first example) means that you'll have to take care of everything related to memory management yourself. Assigning something to that variable will not retain it automatically, not will setting the variable to something else release the previous value.
Defining it as a property creates getter and setter methods under the hood. Most importantly, if you use it with the "retain" keyword, your setter method will retain the new value (and release the old one if there was one).
Note that the setter method will only be invoked if you use the dot notation, e.g., self.myStr = #"new string", or the method call, e.g., [self setMyStr:#"new string"]. If you just call myStr = #"new string" the setter method will not be called and you need to release the old value yourself and retain the new one.
I don't think the first case shows an autoreleased object, it would all depend on how you managed the creation and the destruction of that particular object. If for instance when you create that object you call:
//This string will indeed be autoreleased
theStr=[NSString stringWithString:#"Jibber jabber"];
//Or even
theStr=#"Jibber jabber";
But you have to take charge of the memory management if you create it in the following way:
//Manage my memory
theStr=[[NSString alloc] init];
//You have to release this property on the dealloc method
-(void)dealloc{
[theStr release];
[super dealloc];
}
On your second example, you create a setter and a getter method for the property theStr and by adding the nonatomic attribute, you make your property not thread safety, meaning that a thread can begin to modify your property while another one is already editing it. And by setting the retain attribute to your property, the setter method will be synthesized the following way:
- (void) setTheStr:(NSString *) newString {
[newString retain];
[theStr release];
theStr = newSupervisor;
}
You can consult more about this in one of my favorite books, Learning Objective-C 2.0 in chapter 12.
Maybe someone could explain the difference between property:
in .h file
#property(nonatomic,retain) NSString *someString;
#property(nonatomic,retain) NSString *someString2;
in .m file
#synthesize someString = _someString;
or
#synthesize someString2;
what is the difference for _someString and self.someString2 using in controller?
and in dealloc how i should release these property's
[_someString release];
AND
[self.someString2 release];
OR
_someString = nil;
_someString2 = nil;
synthesize someString = _someString;
This says synthesize the property someString but for direct access, use _somestring.
synthesize someString2;
This says synthesize the property someString2 but for direct access, use someString2.
Think of it as if the compiler is generating the iVars for you but in the first case the iVar is called _someString and the second is called someString2
This is a common usage (I recently moved to it) so that when you are dealing with the object directly (such as initialisers or in dealloc, where you should't use self) you can see instantly that when you write _someString = #"aString"; you are not going through the property methods that would apply the memory management types (such as retain, or copy). It used to be common that people would assign values directly, and then wonder why they weren't being retained.
[_someString release];
[_someString2 release];
Is sending the release method directly to the object.
self.someString = nil;
self.someString2 = nil;
Sends release through the property. In this case, There is no difference. There would be a difference if you were allocating objects: for example:
_someString = someOtherString;
Is a leak (except under ARC, which I will come to later), because you are just putting in a new object to the store, without releasing the current object.
self.someString = someOtherString;
does not leak anything, because the sythesized setter will release the current object before setting (and retaining) the new object.
I said I'd come to ARC. In which case you can't call release anyway, so the questions don't arise, but _someString = someOtherString is not a leak, because the compiler will deal with releasing the current object for you.
After:
property(nonatomic,retain) NSString *someString;
property(nonatomic,retain) NSString *someString2;
and:
#synthesize someString = _someString;
#synthesize someString2;
someString is a property backed by the instance variable _someString. Memory retention and release is managed by Obj-C.
Assignments to someString should use the form self.someString within the class, and must use <reference>.someString outside of it. Except within an initializer there should never be any assignments to a plain _someString.
Reading the value can use simply _someString within the class, but self.someString is also valid, and must use <reference>.someString outside of it.
Releasing the value must use the form self.someString = nil within the class, and <reference>.someString = nil outside of it.
someString2 is similar except it is backed by an automatically named instance variable, which happens to be called someString2.
#synthesize someString = _someString; Means you're making a property with a different name then the member variable it's associated with. This is fine. Typically they are same name. Here's an example when that isn't the case. So someString would be your property and _someString is your member variable.
As for [_someString release]; and [self.someString2 release]; what you're seeing is release being called on the member variable of your class(Which is _someString). [self.someString2 release] calls release on whatever the property returns. Keep in mind that properties can do more then just simply get and set. They are methods just like any other you might right.
Also, don't do [self.someString2 release]; Instead do self.someString2 = nil; That will release it on your behalf. That way it nils out the string. That will protect you from accessing bad memory incase the string is actually deallocated.
_someString = nil won't release your property.
In this case _someString and self._someString point to the exact same object, so you can release using either.
[_someString release];
AND
[self.someString2 release];
releases twice, that's wrong. Use
_someString = nil;
_someString2 = nil;
simply sets your ivars to nil, it doesn't release them, so that's again wrong.
Correct: either
self.someString = nil;
self.someString2 = nil;
or
[_someString release];
[_someString2 release];
I'd recommend the first one (dot-notation), as it does the right thing (you don't know what kind of code does a compiler generate when synthesizing your accessors...)
Basically I have this scenario going on:
//in interface header
#property(nonatomic,retain)OtherClass *otherClass;
//implementation
- (id)initWithOtherClassInstance:(OtherClass*)otherClass
{
if (self != [super init])
return self;
self.otherClass = otherClass;
return self;
}
- (void)dealloc
{
//Do I need to release otherClass ?
[otherClass release];
[super dealloc];
}
I'm wondering whether I should release an instance variable on which not explicitly alloc, new or copy was called? The memory management guides say I shoud not, but what I'm worrying about is that self.otherClass = otherClass would retain the instance variable and thus cause a leak when I would decide to not release it in the dealloc method.
Moreover releasing the instance variable in the dealloc method does not generate an exception, which it would in case it was overreleased.
Does my reasoning here make any sense, and what is the best thing to do in a case like this ?
Yes you do need to release this, as other answers suggest. But I find that explicitly calling [foo release] on an ivar that you retained via property setter to be a little unbalanced. I prefer setting self.otherClass = nil; in these scenarios.
Of course under the hood it will do a release for you, but it just looks more balanced and clean.
You are doing this right, the rule you mentioned is the 'create' rule. You still need to match all your retains with releases as well.
Your init method is wrong. You need to assign the result of [super init] to self.
Other than that, assuming that self.otherClass is a retain property, what you have done is sort of OK. If you insist on using the property in -init you should assign the property to nil in dealloc, as Ben says, because then whether the property is assign, retain or copy, the right thing will happen.
However,
it is recommended that you do not use accessors in the -init and -dealloc methods. This is because subclasses may override them to do things you don't expect and KVO observers might get notified in dealloc. So you should probably just set and retain the ivar in init and release it in dealloc.
Note that
self.otherClass = otherClass
is the same as
[self setOtherClass:otherClass]
The default implementation on setOtherClass: looks like
- (void) setOtherClass:(OtherClass*)other
{
[other retain];
[otherClass release];
otherClass = other;
}
As you can see, it retains the object, so you have to release it somewhere.
If you don't like explicit release without explicit alloc, new or copy, then you can do the next in dealloc:
- (void) dealloc
{
[self setOtherClass:nil];
[super dealloc];
}