The retainCount is
the number of ownership claims there are outstanding on the object
. 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.
What’s a difference between copy and retain?
Retain increases the retain count of an object by 1
and takes ownership of an object. Whereas copy will copy the data present in the memory location and will assign it to the variable so in the case of copy you are first copying the data from a location assign it to the variable which increases the retain count.
Does copy increase retain count?
No, a copied object will have a retain count of 1
, just like a newly initialized object. I highly recommend you read the Memory Management Guide if you wish to learn more.
What is retain in IOS?
You send an object a retain message when you want to prevent it from being deallocated until you have finished using it. An object is deallocated automatically when its reference count reaches 0 . retain
messages increment the reference count
, and release messages decrement it.
What is copy Objective C?
“The copy attribute is an alternative to strong. Instead of taking ownership of the existing object, it
creates a copy of whatever you assign to the property, then takes ownership of that
. Only objects that conform to the NSCopying protocol can use this attribute…”
What is retain and release?
The
system that Objective-C uses
is called retain/release. The basic premise behind the system is that if you want to hold on to a reference to another object, you need to issue a retain on that object. … When that count reaches zero, the object is released and the memory is recovered.
Why retainCount should never be used in shipping code?
You should never use -retainCount ,
because it never tells you anything useful
. The implementation of the Foundation and AppKit/UIKit frameworks is opaque; you don’t know what’s being retained, why it’s being retained, who’s retaining it, when it was retained, and so on.
What is the difference between assign and retain keywords?
Since
retain
is only for object (instanciated in the Heap), basic C type property (bool, int, float, struct…), since they are instanciate in the Stack, should be mark assign. If you see retain in a piece of code, it’s just that this class is not using ARC and it’s just memory management code.
What is a memory leak iOS?
A memory leak occurs
when allocated memory becomes unreachable and the app can’t deallocate it
. Allowing an allocated-memory pointer to go out of scope without freeing the memory can cause a memory leak. A retain cycle in your app’s object graph can also cause a memory leak.
What is weak and strong in Swift?
In Swift,
strong references are the default
, so to make a reference weak you can use the weak keyword. Unlike strong references, a weak reference
What is a property in Objective-C?
Properties in Objective-C are
used to store data in instances of classes
. They define memory management, type, and access attributes of the values they store such as strong , weak , assign , readonly , readwrite , etc. … strong , weak , assign property attributes define how memory for that property will be managed.
What is assign property in Objective-C?
assign is
a property attribute tells the compiler how to synthesize the property’s setter implementation
.
What is NSCopying?
A protocol that objects adopt to provide functional copies of themselves
.
What is the difference between retain and assign in IOS?
Since
retain
is only for object (instanciated in the Heap), basic C type property (bool, int, float, struct…), since they are instanciate in the Stack, should be mark assign. If you see retain in a piece of code, it’s just that this class is not using ARC and it’s just memory management code.
How do I use Dealloc in Objective C?
dealloc is called as a result of memory management. Once an objects “retainCount” reaches 0 then a dealloc message is automatically sent to that object. You should never call dealloc on objects unless it is a call to [
super dealloc];
at the end of an overridden dealloc.
