iOS学习笔记 strong与copy 深浅复制

</pre><p></p><pre name="code" class="objc">

strong copy 对一般的对象没有什么区别，但是对于array string 有一些注意的地方

1.当strong与copy用在NSArray对于对象来说没有太大的区别

@interface ViewController ()
@property (nonatomic, strong) NSArray *arrayS;
@property (nonatomic, copy) NSArray *arrayC;
@property (nonatomic, strong) NSMutableArray *arrayMS;
@property (nonatomic, strong) NSString *str;
@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
NSArray *a = [[NSArray alloc] initWithObjects:@"hello", nil];
self.arrayC = a;
self.arrayS = a;

NSLog(@"数组a ---%p -- %@", a,a);
NSLog(@"arraryC ---%p -- %@", self.arrayC,self.arrayC);
NSLog(@"arraryS ---%p -- %@", self.arrayS,self.arrayS);

}

结果：

2016-08-15 16:28:18.571 copydemo[64461:12400898] 数组a ---0x7fe140518c10 -- (
hello
)
2016-08-15 16:28:18.571 copydemo[64461:12400898] arraryC ---0x7fe140518c10 -- (
hello
)
2016-08-15 16:28:18.571 copydemo[64461:12400898] arraryS ---0x7fe140518c10 -- (
hello
)

由结果可知都是指向同一个对象地址a，此刻a的retainCount＝3

2.在指向NSMutableArray

@interface ViewController ()
@property (nonatomic, strong) NSArray *arrayS;
@property (nonatomic, copy) NSArray *arrayC;
@property (nonatomic, strong) NSMutableArray *arrayMS;
@property (nonatomic, strong) NSString *str;
@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
NSMutableArray *a = [[NSMutableArray alloc] initWithObjects:@"hello", nil];
self.arrayC = a;
self.arrayS = a;

NSLog(@"数组a ---%p -- %@", a, a);
NSLog(@"arraryC ---%p -- %@", self.arrayC,self.arrayC);
NSLog(@"arraryS ---%p -- %@", self.arrayS,self.arrayS);
[a addObject:@"world"];
NSLog(@"数组a ---%p -- %@", a, a);
NSLog(@"arraryC ---%p -- %@", self.arrayC,self.arrayC);   //copy 深复制， a变化不会影响arrayC

执行结果：

2016-08-15 16:31:35.410 copydemo[64478:12421035] 数组a ---0x7feda1619fc0 -- (
hello
)
2016-08-15 16:31:35.410 copydemo[64478:12421035] arraryC ---0x7feda161ab60 -- (
hello
)
2016-08-15 16:31:35.410 copydemo[64478:12421035] arraryS ---0x7feda1619fc0 -- (
hello
)
2016-08-15 16:31:35.410 copydemo[64478:12421035] 数组a ---0x7feda1619fc0 -- (
hello,
world
)
2016-08-15 16:31:35.410 copydemo[64478:12421035] arraryC ---0x7feda161ab60 -- (
hello
)
2016-08-15 16:31:35.410 copydemo[64478:12421035] arraryS ---0x7feda1619fc0 -- (
hello,
world
)

有结果可知：

copy是进行了一次深复制对这次引用，而strong还是指向原来的对象浅复制

3.对于 ［a copy］［a mutableCopy］区别

如果a是NSArray 则［a copy］是浅复制，［a mutableCopy］是深复制

如果a是NSMutableArray 则［a copy］［a mutableCopy］都是深复制