什么是属性复制意味着在Cocoa的框架？（像UITabBar的items属性） [英] what's property copy means in Cocoa's Framework?(like UITabBar's items property)

问题描述

在UITabBar.h中，一个签名的副本

In UITabBar.h, a propery signed copy

@property（nonatomic，copy）NSArray * items; // get / set visible

@property(nonatomic,copy) NSArray *items; // get/set visible

这是一个数组
copy是什么意思？
copy NSArray container obj？
copy每个obj NSArray包含？
或某事。

It's a array And what "copy" means? copy NSArray container obj? copy every obj NSArray contains? or something.

UITabBar* testBar = [[UITabBar alloc] init];
UITabBarItem* item = [[UITabBarItem alloc] init];
NSArray* array = [[NSArray alloc] initWithObjects:item, nil];

NSLog(@"bar:%p,%d", testBar, testBar.retainCount);
NSLog(@"item:%p,%d", item, item.retainCount);
NSLog(@"array:%p,%d", array, array.retainCount);

testBar.items = array;

NSLog(@"that item:%p,%d", [testBar.items lastObject], [[testBar.items lastObject] retainCount]);
NSLog(@"testBar.items:%p,%d", testBar.items, testBar.items.retainCount);

result

bar：0x96a9750,1

result

bar:0x96a9750,1

项目：0x96aa230,2

item:0x96aa230,2

array：0x96aa280,1

array:0x96aa280,1

该项目：0x96aa230,2

that item:0x96aa230,2

testBar.items：0x96aa280,6

testBar.items:0x96aa280,6

推荐答案

在这种情况下，没有复制的原因是 NSArray 是 immutable 。你不需要做一个副本，以防止对数组的更改，因为这样的更改不能做;

The reason the copy has not been made in this case is that NSArray is immutable. You do not need to make a copy of it to guard against changes to the array, because such changes cannot be made; it is sufficient to retain the same immutable array.

如果你使用 NSMutableArray 尝试这个实验，你会得到一个不可变的数组。不同的结果。

If you try this experiment with NSMutableArray, you will get a different result.

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