This document discusses property and memory management in Objective-C. It covers properties, including attributes like accessor, writability, and atomicity. It then discusses object ownership and memory management, comparing manual reference counting (MRC) to automatic reference counting (ARC). ARC provides automatic memory management of Objective-C objects and avoids issues like retain cycles seen in MRC. The document provides examples and references for further reading.

1. Property And Memory Management
in Objective-C
By Yoyo Chen

2. AGENDA
• 1.Property
• 2.Object ownership
• 3.Memory Management

3. PROPERTY
• Objective-C properties ;
a way to encapsulate an object’s values
Ref: http://rypress.com/tutorials/objective-c/properties.html

4. Property Attribute
Attribute Usage
Accessor Getter/Setter method
Writablity readwrite, readonly
Semantics Without ARC retain/assign/copy
With ARC strong/weak/copy/unsafe_unretained
Atomicity atomic / nonatomic; Default:atomic

5. ACCESSOR
• Use Accessor Methods to Get or Set Property Values
• Accessor methods are synthesized automatically by the compiler
@property float heightInMeters;
@synthesize heightInMeters;
Getter method : heightInMeters
Setter method : setHeightInMeters
[person setHeightInMeters:1.9];
float height = [person heightInMeters];

6. DOT SYNTAX
• A concise Alternative to Accessor Method Calls
• float height = person.heightInMeters;
• person.heightInMeters = 1.9;

7. Atomic v.s nonatomic (1)
Atomic
• Is default behavior
• Use in multi-threaded code
Non-Atomic
• Make setter method faster than atomic
• Not thread safe
• May result in unexpected behavior, when two different process access the same
variable at the same time
Advice: I don’t think you will write multi-threaded code anytime soon. And when you do, I
don’t think atomic setter methods are going to help.
1.Objective-C Programming: The Big Nerd Ranch Guide :page 220
2. http://stackoverflow.com/questions/588866/atomic-vs-nonatomic-properties

8. Atomic v.s nonatomic (2)
Advice:
I don’t think you will write multi-threaded code anytime soon.
And when you do, I don’t think atomic setter methods are going to help.
Objective-C Programming: The Big Nerd Ranch Guide :page 220

9. • Memory Management
1.MRC(manual reference counting)
2.ARC(automatic reference counting)

10. http://en.wikipedia.org/wiki/Automatic_Reference_Counting#Property_Declarations

11. MRC (Manual Reference Counting)
https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/MemoryMg

12. Automatic Reference Counting (ARC)
• A compiler feature that provides automatic memory management of Objective-C objects.
• Rather than having to think about retain and release operations, ARC allows you to
concentrate on the interesting code.
• ARC is supported in Xcode 4.2 or later,
Mac OS X 10.6 or later, and iOS 4.0 or later(partially support), .

13. Transitioning to Automatic Reference Counting (ARC)
https://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introdu

14. ARC (Automatic Referencing Counting)
• Pointers keep objects alive
• If fisrName is a strong pointer , firstName is the owner of @”Ray” object
• weak pointer, not the owner
Ref:http://www.raywenderlich.com/5677/beginning-arc-in-ios-5-part-1

15. EX.

16. • Revise First Name

17. • Click update
http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/ProgrammingWithObjectiveC/Encaps

18. • Zeroing Weak References
Only available in Mac OS X ≥ 10.7 and iOS ≥ 5
Ref:http://www.raywenderlich.com/5677/beginning-arc-in-ios-5-part-1

19. • Avoid Retain Cycle
Ref :http://ios.sodas.tw/ntumpp-2012f/files/Lecture-2-iOS-in-Developers-view.pdf

20. • Avoid Retain Cycle
Ref :http://ios.sodas.tw/ntumpp-2012f/files/Lecture-2-iOS-in-Developers-view.pdf

21. Ref :http://ios.sodas.tw/ntumpp-2012f/files/Lecture-2-iOS-in-Developers-view.pdf

22. ARC limitation
• ARC does not automate malloc/free, management of the lifetime of Core Foundation
objects, file descriptors, and so on, you still free such resources by writing
a dealloc method.
http://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduct

24. DEMO
• Memory leak: retain cycle

25. Objective-C Programming: The Big Nerd Ranch Guide :page 125

26. • Product  Profiler ->
http://developer.apple.com/library/ios/#documentation/DeveloperTools/Conceptual/InstrumentsUserGuide/Mem