Question

In UITabBar.h, a propery signed copy

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

It’s a array
And what “copy” means?
copy NSArray container obj?
copy every obj NSArray contains?
or something.

so there’s a test

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

item:0x96aa230,2

array:0x96aa280,1

that item:0x96aa230,2

testBar.items:0x96aa280,6

why neither container array nor obj in array has been “copied”?

Answer 1

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.

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