IOS review notes 9: ARC function, ios review notes arc

IOS review notes 9: ARC function, ios review notes arc
1. Introduction to ARC
ARC is a function of the editor.
It will automatically release the alloc objects.
It automatically generates the release in dealloc for variables using the retain attribute;

When you select the ARC function when creating a project, you cannot call it:
Retain
RetainCount
Release
Autorelease
[Super dealloc]


Second ARC judgment criteria
1 criterion: as long as there is no strong pointer object, the object will be destroyed.


2 pointers are divided into two types:
1 strong pointer: _ strong. By default, all pointers are strong pointers.
2. weak pointer: _ weak. If the weak Pointer Points to an object that does not exist, it will be cleared.


Example of code with three strong pointers:

Person * p = [[Person] init]; p = nil; // clear the pointer. If no strong pointer points to the memory object, the object will be released.

Or

P = [[Person] init]; // The Pointer Points to another object. The previously allocated memory object is released.

Person * person1 = [[Person] init]; Person * person2 = person1; person1 = nil; // destroyed after the function is executed

Example of weak pointer code:

Person * person1 = [[Person] init] ;__ weak Person person2 = p; person1 = nil; // destroy the object

Note the following incorrect syntax:

_ Weak Person * person1 = [[Person] init]; // There is a warning that the created object will be immediately released

Four property Parameters
1 strong: used for OC objects. It is a "strong" pointer for member variables.
Strong replaces retain and does not need to be release in dealloc. The function is the same as retain.
For example:
@ Property (nonatomic, strong) Book * book;


2 weak: used for OC objects. The "weak" pointer in member variables
Strong replaces assign. When the book points to the object for destruction, it is automatically cleared.
@ Property (nonatomic, weak) Book * book;


3 assign: used for basic data types


V. ARC Conversion Function of Xcode
1 Project to ARC
Edit-> Refactor-> Convert to Object-c arc, check, next;
A preview is displayed. We can see that release and autorelease are deleted,
The retain of property becomes strong.
Click Save and Enable.



2 compatible with non-ARC
Click project-> Build Phases: Complie Source to view the Source files in the project,
Press enter, and enter:
-Fno-objc-arc
In this way, you can use non-ARC-related items in this file.


3. ARC compatibility with non-ARC Projects
In 2, enter:
-F-objc-arc
In this way, the ARC files can be compatible in non-ARC projects.


Circular references in section 6 ARC
Mutual objects, set the property with a short life cycle to weak