strong和copy

//定義Person類
@interface Person : NSObject
@property (nonatomic, strong) NSArray *array1;
@property (nonatomic, copy) NSArray *array2;
@end

//在ViewController中
@implementation ViewController
- (void)viewDidLoad {
	[super
 
 viewDidLoad];
	
	NSMutableArray *arrayM = [NSMutableArray arrayWithObject:@"one"];

	Person *person = [[Person alloc] init];
	person.array1 = arrayM;
	person.array2 = arrayM;
	
	[arrayM addObject:@"two"];
	
	NSLog(@"\n array1:%@ \n array2:%@ \n", person.array1, person.array2);
}
@end

最終列印結果為:

array1:
 
(
	one,
	two
)
array2:(
	one
)

當使用strong時,array1和arrayM都指向同一塊記憶體區域,當arrayM改變時,array1的內容也會改變,兩者是一樣的
當使用copy時,array2在賦值之前,將arrayM內容複製,建立一塊新的記憶體空間,所以兩者不同,不會隨它改變

歸根結底,不同修飾符,對應的setter方法不同
strong對應的setter方法,是將_property先release([_property release]),然後將引數retain([property retain]),最後_property = property