iOS属性声明澄清

问题描述

这是一个两部分的问题，希望我能够更深入地了解这个主题。

1）在我看来，在目标c 中，有两个选项用于声明类的属性。一个是将属性添加到标题的类体例如。

  @interface MyClass：NSObject {
 NSArray * myArray ; 
} 
  

也可以在 @interface 正文和 @end 语句之前。

  @interface MyClass：NSObject {
 // 
} 
 
 @property（nonatomic，retain）NSArray * myArray; 
  

这两种样式有什么区别，以及何时选择 @property 之后，您可以找到之类的选项>（nonatomic，retain）。

解决方案

这里是唯一的Xcode可识别的属性修饰符：

• 非原子属性，主要用于整个程序中只使用一个线程时）


• atomic （默认）


• 保留 / strong （自动保留/释放集合上的值，确保值不会意外释放）（默认值为ARC和对象类型）


• readonly （不能设置属性）


• readwrite
  
• assign / unsafe_unretained （不使用此属性进行内存管理，手动分配值）（如果不是ARC或对象类型，则为默认值）


• copy


• weak （自动将零值设置为零）引用应该释放对象，并且不保留传递的值）


• getter = method 此属性的值）


• setter = method （设置用于设置此属性值的选择器）

This is a two part question in hopes that I can understand more about the topic.

1) It seems to me that you have two popular options for declaring a property for a class in objective c. One is to add the property to the header's class body eg.

@interface MyClass : NSObject {
    NSArray *myArray;
}

Or you can add it after the @interface body and before the @end statement like so.

@interface MyClass : NSObject {
    //
}

@property (nonatomic, retain) NSArray *myArray;

What is the difference between these two "styles" and when do you choose one over the other?

2) after the @property you find options such as (nonatomic, retain). What are those for and why/when do you use different options?

解决方案

Here are the only property modifiers that Xcode recognizes:

• nonatomic (does not enforce thread safety on the property, mainly for use when only one thread shall be used throughout a program)
• atomic (enforces thread safety on the property, mainly for use when multiple threads shall be used throughout a program) (default)
• retain / strong (automatically retains / releases values on set, makes sure values do not deallocate unexpectedly) (default if ARC and object type)
• readonly (cannot set property)
• readwrite (can both set and get property) (default)
• assign / unsafe_unretained (no memory management shall be done with this property, it is handled manually by the person assigning the value) (default if not ARC or object type)
• copy (copies the object before setting it, in cases where the value set must not change due to external factors (strings, arrays, etc).
• weak (automatically zeroes the reference should the object be deallocated, and does not retain the value passed in)
• getter=method (sets the selector used for getting the value of this property)
• setter= method (set the selector used for setting the value of this property)

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