I found that the iphone have viewDidUnload, and dealloc. I want to release the object. Which method should I use to release the object? What's the different between them?
Send release or autorelease to release an object. You shouldn't send dealloc; the Obj-C runtime will do that.
If you're asking where you should release an owned object, read: "When should I release objects in -(void)viewDidUnload rather than in -dealloc?"
Do not call dealloc. Use the retain-release model for memory management, and Objective-C will take care of deallocating memory for you.
See this link for a good explanation of how retain-release works.
The difference is that viewDidUnload is used to release "spare" objects in low memory situations while dealloc is used to release all objects when the view is no longer needed.
This means that you will almost always have a dealloc method but have a viewDidUnload method only where it makes sense.
Related
I am new to iphone and I want to know when does -(void) dealloc method call. I know it is used to release objects but can we release any kind of object using dealloc method? And is it necessry to add this method and why we write [suped dealloc] in dealooc method?
share your views.
Here is the explanation straight from APPLE's Docs
The NSObject class defines a method, dealloc, that is invoked
automatically when an object has no owners and its memory is
reclaimed—in Cocoa terminology it is “freed” or “deallocated.”.
Important
Never invoke another object’s dealloc method directly.
Here is the answer why we call [super dealloc]?
You must invoke the superclass’s implementation at the end of your
implementation. You should not tie management of system resources to
object lifetimes
When an application terminates, objects may not be sent a dealloc
message. Because the process’s memory is automatically cleared on
exit, it is more efficient simply to allow the operating system to
clean up resources than to invoke all the memory management methods.
You Can release object those which is allocted, copy, or retain by you this is simple to understand. You can not release object those are not allocating by you means autorelease object, which ios detect for no more use in memory ,that time autorelease pool drain that time those object released from memory automatically.
And object dealloc method called when object retain count becomes zero.
You never send a dealloc message directly. Instead, an object’s dealloc method is invoked indirectly through the release NSObject protocol method (if the release message results in the receiver's retain count becoming 0). See Memory Management Programming Guide for more details on the use of these methods.
Subclasses must implement their own versions of dealloc to allow the release of any additional memory consumed by the object—such as dynamically allocated storage for data or object instance variables owned by the deallocated object. After performing the class-specific deallocation, the subclass method should incorporate superclass versions of dealloc through a message to super:
Refer this Link
Should I implement dealloc in my app delegate and release my ivars there? As I understand it, when an app gets terminated, all the memory associated with it gets freed automatically. So basically, there's no need to release any ivars yourself at termination.
I've found this question here already: Does it make any sense to release ivars in appdelegate's dealloc?
One of the answers says that objects might have clean up code in dealloc, so you might want to release ivars yourself at termination. But when I put an NSLog in the dealloc of my app delegate, it's never called. My assumption is there's no use at all for it so I don't even have to implement it, am I right?
It may be necessary in future iOS releases. For the sake of forward compatibility, and since Apple seems to recommend it I would release those ivars.
You are right, you don't need to release your ivars in dealloc (The example templates that come with the SDK do have a -dealloc though). The OS will reclaim any memory associated with you app. If anything, it will just add a small amount of overhead. Also, as far as I know, there isn't any guarantee by the environment that the -dealloc in your app delegate will ever get called, so it may never even execute.
Iam having a very basic doubt in memory management. If suppose iam allocating memory for an object in viewWillAppear method. Should i release the object in viewWillDisappear method or in the release all the objects in the de
It's dependent when you want to release the object. You don't have to release on viewWillDisappear. But, you can, just think about when you need it and when you don't. Technically, either one is fine. Depending on the situation though I would think: if you need the object for multiple views don't dealloc in viewWillDisappear, if you need it only for that view and you don't need it again, dealloc in viewWillDisappear.
Here's a very easy to learn tutorial on objective-c memory management.
http://cocoadevcentral.com/d/learn_objectivec/
You'll learn a lot about retaining and releasing variables. In general variables are defined according to scope (i.e where they will be used) For example, you may want to initialize a variable that's used throughout a class in viewDidLoad and release it in dealloc. It all depends on where you need to store data and for how long.
I'm developing an iPhone application, and I very new on iPhone development.
I've created some custom classes with instance variables (NSArray, NSString, etc.). All classes inherits from NSObject.
Should I create a dealloc method to release all instance variables?
Thank you.
Yes, you definitely need a dealloc if you are keeping instance variables that are objects. You will also probably need to retain or copy those as well, depending on how your object creates/uses them.
Check out this article on memory management. I think it explains it pretty well. You must also read the Memory Management Programming Guide for Cocoa. Even if you don't fully understand everything, read the whole thing through, then read the article, then do some work, get some crashes and read it again :) eventually it should all click.
In iPhone development its pretty much SOP to have a dealloc since there is no garbage collection.
You have to release any object your class has ownership for. That means, yes you have to overwrite the dealloc method and release the objects there.
Normally you have ownership over values (objects) in instance variables, but it also depends own how you create them.
You should definitely read the Memory Management Programming Guide, it describes pretty well when you gain ownership.
Yes, having a dealloc method is normally the best way.
If you want to reclaim memory used by your instance variables you will have to release them when you are done with them. You could add a method to do this clean up:-
- (void)cleanUp {
[myArray release];
[myString release];
}
Call it when you no longer need the instances.
Now, the chances are that the point in time when you want to release these variables is the point in time when their parent object is destroyed (parent object is gone, so instance variables are no longer needed). As -dealloc is automatically called for you when the parent object is going to be destroyed - it makes more sense to put the cleanup code in dealloc than in our -cleanup method that we have to call at the right time.
If you don't want to reuse the memory, eg. if you are never going to be finished with the instance variables, then you don't need to release them and might not need a -dealloc.
I am wondering what the difference is between release and dealloc? After reading, the memory management rules (See below)., I am thinking most of the time I will be using release. However, I wanted to know what to do for properties.
#property(retain)....
I have been using dealloc but after reading this article I am not sure that is correct.
You take ownership of an object if you create it using a method whose name begins with “alloc” or “new” or contains “copy” (for example, alloc, newObject, or mutableCopy), or if you send it a retain message. You are responsible for relinquishing ownership of objects you own using release or autorelease. Any other time you receive an object, you must not release it.
You should never call dealloc on anything other than super.
The only time you will be calling dealloc is in the dealloc method of a custom inherited object, and it will be [super dealloc].
When the retain count of an object goes down to zero, dealloc will automatically be called for you, so in order to manage memory properly, you need to call retain and release when appropriate.
If this isn't clear to you or you'd like details about how memory is managed in Cocoa, you should read the Memory Management Programing Guide.
You never call dealloc directly. It is invoked by the system when the retainCount of the object goes to 0. Every time you do a retain, the retainCount is incremented with 1. Every time you do a release, it gets decremented. This way, by balancing your retains and releases, you ensure than when the retainCount gets to 0, dealloc will be automatically called, and your object freed.
As Ben S noted, the only time and place you would call dealloc is in in the dealloc method of an inherited object.
When you use #property(retain) and then #synthesize to generate the property code, you do not need to do any manual memory management on the property. The other answers are correct in that you shouldn't be using dealloc except in your own override of a parent class dealloc.