ARC下strong和copy修饰数组的区别

ARC模式新加入了strong修饰符,strong相当于MRC下的Retain,不过strong是强引用.下面介绍一下strong和copy的区别,具体看代码

@interface People : NSObject

@property (nonatomic,copy)NSString *name;


@end

@implementation People

@synthesize name;

@end

@interface ViewController ()

@property (nonatomic,copy)NSArray *copyarr;
@property (nonatomic,weak)NSArray *strongarr;

@end

创建People类,在VC中声明2个属性,一个是copy修饰的数组,一个是strong修饰的数组;

    People *p1 = [[People alloc] init];
    p1.name = @"张三";
    People *p2 = [[People alloc] init];
    p2.name = @"李四";
    NSMutableArray *arr = [NSMutableArray arrayWithArray:@[p1,p2]];;
    self.copyarr = arr;
    self.strongarr = arr;
    
    People *p3 = [[People alloc] init];
    p3.name = @"王五";
    
    [arr addObject:p3];

创建3个people对象,设置不同的name,创建一个可变数组arr,将p1,p2,加入arr中,让copyarr和strongarr分别指向arr,

再将p3加入arr数组.copy会将数组复制一份,strong则是将指针指向数组,为了验证,添加打印

    NSLog(@"copyarr:%p",self.copyarr);
    NSLog(@"strongarr:%p",self.strongarr);
    NSLog(@"arr:%p",arr);
    
    for (People *p in self.copyarr) {
        NSLog(@"copyarr:%@,%p",p.name,p);
    }
    
    for (People *p in self.strongarr) {
        NSLog(@"strongarr:%@,%p",p.name,p);
    }
    

打印结果如下

2015-12-29 10:28:20.134 Testdemo2Delete[1174:43789] copyarr:0x7fb1d9579e00
2015-12-29 10:28:20.134 Testdemo2Delete[1174:43789] strongarr:0x7fb1d9510260
2015-12-29 10:28:20.135 Testdemo2Delete[1174:43789] arr:0x7fb1d9510260
2015-12-29 10:28:20.135 Testdemo2Delete[1174:43789] copyarr:张三,0x7fb1d9514c00
2015-12-29 10:28:20.135 Testdemo2Delete[1174:43789] copyarr:李四,0x7fb1d95158d0
2015-12-29 10:28:20.135 Testdemo2Delete[1174:43789] strongarr:张三,0x7fb1d9514c00
2015-12-29 10:28:20.135 Testdemo2Delete[1174:43789] strongarr:李四,0x7fb1d95158d0
2015-12-29 10:28:20.135 Testdemo2Delete[1174:43789] strongarr:王五,0x7fb1d9578500

可以看到,copy修饰的数组地址和arr(源数组)的地址不一样,并且copyarr中只用p1和p2, 可以证明copy是将源数组copy了一份(重新开辟了空间)并将指针指向新的空间;strong的地址和arr的地址一样,可以知道,strong指向的还是源数组,对象是一样的.