I am trying to convert an old code to an ARC code.
However, i am getting a build error at the following line
[[token retain] autorelease];
I get 3 errors in the following order:
-'autorelease' is unavailable: not available in automatic reference counting mode
-[rewriter] it is not safe to remove an unused 'autorelease' message; its receiver may be destroyed immediately
-ARC forbids explicit message send of 'autorelease'
If i remove this particular line, then the code compiles correctly
If that is all that is on the line, you can probably just remove it. That code claims a reference to the object but also says you don't want to worry about releasing later, but with ARC you don't have to worry about it.
I am guessing that Xcode did not get rid of it automatically because of lack of context. If it had been in a more common location, such as in a return statement, it would be obvious what the intent was. When it is all by itself, it could be, but probably is not, something more complicated.
ARC manages your memory for you, so you don't need to call "autorelease", "release", "retain" etc. With ARC the compiler retain and release objects as necessary for you so you don't have to explicitly make these calls. If you want to manually manage your memory disable ARC, or you can use the compiler flag "-fno-objc-arc" to disable ARC on a specific class.
ARC means you don't have to use release, retain or those other pesky memory management things. ARC add them all for you automatically when you compile the app. Read more here
If you have old code where it would not be the best solution to remove all the memory management calls, then check this answer to disable ARC for particular files
Related
when i'm trying to build my project I have a new error where objc_retainedObject() is used.
I have the error message objc_retianedObject is unavailable: use CFBridgingRelease() or a (__bridge_transfer id) cast instead.
I replaced the usages of objc_retainedObject() by CFBridgingRelease and there are no longer errors and I can run the app, but when the app is going to display my QRCode-scanning view, it crashed without messages.
It is the same when I put #define objc_retainedObject(o) ((__bridge_transfer id)(objc_objectptr_t)(o)) which was supposed to be a solution.
I believe that it is an XCode configuration or a missing library problem. Any ideas?
Do not recreate objc_retainedObject. It was removed on purpose. CFBridgingRelease and CFBridgingRetain are the correct tools for moving CF objects into ARC. (__bridge is the tool for dealing with CF objects that you don't need to transfer to ARC because you aren't storing them.)
If your program is crashing, you're probably managing memory incorrectly. It is likely that objc_retainedObject was incorrect (even if you happened to get away with it). See when should you use __bridge vs. CFBridgingRelease/CFBridgingRetain? for correct memory management when transferring CF objects to ARC.
Without knowing more about the code, I can't guess exactly where you've made a mistake, but you probably are calling CFBridgingRelease on an object that you didn't acquire via the Create Rule. You don't just throw CFBridgingRelease on every CF object you encounter. You need to make sure you're balancing an existing retain.
Coming from the world of managed memory, wondering what would be the proper way to clean up objects when using ARC.
For example: if declaring an instance variable in C#, .NET will allow the GC to pick it up once it leaves scope (method/loop body, etc)
What's the proper way to clean-up in Objective-C? Just set the reference/pointer to nil or call dealloc or will ARC detect that no external references are pointing to the instance once execution leaves scope and do the job for you?
ARC means "Automatic Reference Counting" and is just a way to let the compiler add the calls to retain/release/autorelease for you. It's not the same as GC but in most cases, you can consider that objects lifetime is automatically managed for you, like in GC.
If you want more information, you should read LLVM document on ARC
Last note: never call dealloc yourself. dealloc is the object's finalizer which is called once the ObjC runtime determines that the object reference count has reached 0. This method is only meant to be overriden by subclasses. In ARC mode, you generally don't need to do that, except if your object references non-object ivars that need to be finalized once the object itself is finalized.
will ARC detect that no external references are pointing to the
instance once execution leaves scope and do the job for you
Basically, yes, that's exactly what ARC will do. You don't need to clean up objects when you're using ARC; in fact, you can't (it stops you from trying to perform manual memory management).
You might want to consult the relevant discussion in my book:
http://www.apeth.com/iOSBook/ch12.html#_memory_management
It explains what's really happening behind the scenes (how memory is actually managed) and then goes on to describe how ARC shields you from most of it.
Note that (as I explain in the URL referenced above) it mostly isn't done by anything like garbage collection: it's done by inserting invisible explicit memory management throughout your code.
Well, in the past, iOS programmers were responsible for telling the system when they were done using an object that they allocated by sending the object a release message. That was done in accordance with a memory management system known as manual reference counting. As of Xcode 4.2, programmers no longer have to worry about this and can rely on the system to take care of releasing memory as necessary. This is done through a mechanism known as Automatic Reference Counting, or ARC for short. ARC is enabled by default when you compile new applications using Xcode 4.2 or later.
You can also disable ARC, in your Xcode interface, go to your main project (not main.h) your actual Xcode project, and select it, you should see a window in Xcode that displays the settings for your project, there will be one that says 'Objective-C Automatic Reference Counting' and it will be set to 'Yes', deactivate it (to 'No') and you shouldn't worry about the ARC, if you come from the world of data management and memory as you said, but keep in mind that it would be easier to you to keep updated to the iOS new features system, that are easier to the programmer to program, it just makes our life easier.
And now, the 'proper way to clean-up in Xcode' with ARC is with 'alloc' and 'init'.
With ARC in Xcode you do not need to worry for 'cleaning' that's the job of Xcode now, you just need to:
1) Create a variable.
2) Allocate.
3) Initialize.
That's it.
An example here:
int main (int argc, char * argv[])
{
#autoreleasepool {
Variable *myVariable;
// Create an instance of a Variable and initialize it
myVariable = [Variable alloc];
myVariable = [myVariable init];
// Set variable to 4/20
[myVariable setNumerator: 4];
[myVariable setDenominator: 20];
// Display the variable using the print method
NSLog (#"The value of myVariable is:");
[myVariable print];
}
return 0;
}
Just allocate and then initialize, yo do not need to do any thing else.
Keep in mind getters and setters.
I believe I successfully converted by app to ARC using the 'Refactor -> Convert to Objective-C ARC' tool but only one of my project targets has the setting:
And if I create anything using IB it is still generating retain / release / dealloc code?
Also I now have crashes I did not before because of memory use, so I am wondering if my project is in a half converted state that is causing me random memory issues.
How do I get these other targets to use ARC - or make sure they are using ARC?
Manually change the flags to say YES. Also want to check and make sure that none of the files have the compiler flag "-fno-objc-arc" set. (I've run into projects that were half converted this way.)
If you're still running into memory issues, run the Leaks Instrument. Even with ARC, you can still have memory leaks like retain cycles where parent-child relationships retain each other. In such a case, you need to use weak pointers.
I just downloaded an Xcode project, and I get all these errors about "ARC Restrictions." What are these, and how can I remove them?
There are basically two versions of memory management in objective-c. ARC and... well, "Not ARC" :-) You probably downloaded a project, which doesn't use ARC already. Simplest way of resolving your problem is to instruct the compiler to treat your sources as "Not ARC". Explained here.
And here is a good tutorial that should get you started with ARC.
ARC automatically keep track of memory release and retain so you can not release and retain any memory manually.
ARC also doesn't allow any method to be get called at compile time which prototype is not declared in interfaces.
It has also introduced new #autoreleasepool block. so it doesn't not allow older autorelease of an object automatically
However it has allowed dealloc method to be written, but it doesn't allowed [super dealloc] to be get called.
There are much more written about ARC at this blog you can checkt it here
You can covert your project to ARC using xcode in following way.
Go to Edit -> Refactor -> Convert to objective c arc.
However it has some compatibility issue with git repository so it does not convert when .git folders are there in projects. so you will have to remove it first and then convert it. check this link
When trying to use -retain, -release, and -dealloc while building my application using automatic reference counting in Xcode 4.2, I get an error like the following:
Automatic Reference Counting forbids
explicit message send of 'dealloc'
Why am I seeing this error? Are -retain, -release, and -dealloc no longer allowed under automatic reference counting?
Basically:
When using ARC, it's all or nothing. Either the compiler is managing all of the retains/releases/deallocs for you, or it is doing nothing. You cannot intersperse your own calls to them, because the compiler wants to do it all itself. It can make absurd optimizations by doing this (for example, a method that returned an autoreleased object under Manual Memory Management may now produce an object that never ends up in an autorelease pool). If you were to start sprinkling in your own calls to retain and release, then the compiler would have to work with these and wouldn't be able to perform a lot of the optimizations that it wants (and that you should want).
And as an added bonus, invoking -retainCount is now a compiler error! OH HAPPY DAY!
in response to AliSoftware: we CNA mix ARTC and not-ARC frameworks, and also arc and not-ARC source.
(I did it..)
The basic ideas are:
1) compiler will insert/remove calls as a very-very-good cocoa programmer can do
2) cocoa is ANYWAY C code, so we have separate compilations, so the linker CAN link binaries produced by multiple sources. Think it as we can mix asm and cocoa, or C and pascal...
in main opinion the Appleadvantege over c# / java is here: we are alway allows to mix, and, using a COMPILER technique 8non a runtime..) we can rush performance beyond.
Under automatic reference counting, retain, release, and dealloc are not allowed.
If you have an existing code, you can keep using it as is with the -fno-objc-arc you can selectively disable ARC on any file.
If you want to disable ARC on MULTIPLE files:
Select desired files at Target/Build Phases/Compile Sources in Xcode
PRESS ENTER. (double click selects only one file)
Type -fno-objc-arc
Press Enter or Done
As I have pointed out in my answer on Xcode ARC, you can compile specific source files as non-ARC. Dave DeLong's answer is a bit off. It doesn't include the fact that you can instruct the compiler to compile source as non-ARC in an ARC-enabled project (as explained here).