Cocoa 框架中的属性副本是什么意思?(如 UITabBar 的 items 属性)

what#39;s property copy means in Cocoa#39;s Framework?(like UITabBar#39;s items property)(Cocoa 框架中的属性副本是什么意思?(如 UITabBar 的 items 属性))

问题描述

在 UITabBar.h 中，一个属性签名的副本

In UITabBar.h, a propery signed copy

@property(nonatomic,copy) NSArray *items;//获取/设置可见

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

这是一个数组复制"是什么意思?复制 NSArray 容器 obj?复制每个 obj NSArray 包含的内容?什么的.

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);

结果

栏:0x96a9750,1

result

bar:0x96a9750,1

项目:0x96aa230,2

item:0x96aa230,2

数组:0x96aa280,1

array:0x96aa280,1

那个项目:0x96aa230,2

that item:0x96aa230,2

testBar.items:0x96aa280,6

testBar.items:0x96aa280,6

为什么容器数组和数组中的obj都没有被复制"?

why neither container array nor obj in array has been "copied"?

推荐答案

这种情况下没有复制的原因是NSArray是不可变的.您不需要复制它来防止对数组进行更改，因为无法进行此类更改；保留相同的不可变数组就足够了.

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.

如果你用 NSMutableArray 尝试这个实验，你会得到不同的结果.

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

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