strong，copy有何不同？实践出真知！上代码
strong
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic,strong)NSString *name;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
NSMutableString *string = [[NSMutableString alloc] initWithString:@"张三"];
self.name = string;
NSLog(@"string:%@, 地址:%p", string, string);
NSLog(@"self.name:%@, 地址%p", self.name, self.name);
[string appendString:@"1"];
NSLog(@"string:%@, 地址:%p", string, string);
NSLog(@"self.name:%@, 地址%p", self.name, self.name);
}
@end
运行结果
2021-06-04 22:54:17.867578+0800 iOSDemo[1557:53589] string:张三, 地址:0x6000008aecd0
2021-06-04 22:54:17.867716+0800 iOSDemo[1557:53589] self.name:张三, 地址0x6000008aecd0
2021-06-04 22:54:17.867810+0800 iOSDemo[1557:53589] string:张三1, 地址:0x6000008aecd0
2021-06-04 22:54:17.867893+0800 iOSDemo[1557:53589] self.name:张三1, 地址0x6000008aecd0
copy
//
// ViewController.m
// iOSDemo
//
// Created by 彭之耀 on 2021/6/4.
//
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic,copy)NSString *name;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
NSMutableString *string = [[NSMutableString alloc] initWithString:@"张三"];
self.name = string;
NSLog(@"string:%@, 地址:%p", string, string);
NSLog(@"self.name:%@, 地址%p", self.name, self.name);
[string appendString:@"1"];
NSLog(@"string:%@, 地址:%p", string, string);
NSLog(@"self.name:%@, 地址%p", self.name, self.name);
}
@end
运行结果
2021-06-04 22:56:08.281057+0800 iOSDemo[1582:54701] string:张三, 地址:0x6000008c5110
2021-06-04 22:56:08.281187+0800 iOSDemo[1582:54701] self.name:张三, 地址0x6000006b6240
2021-06-04 22:56:08.281303+0800 iOSDemo[1582:54701] string:张三1, 地址:0x6000008c5110
2021-06-04 22:56:08.281394+0800 iOSDemo[1582:54701] self.name:张三, 地址0x6000006b6240
分析
- 当我们进行赋值的时候，
strong是直接将地址值传递给了对象的属性，而copy是开辟了新的空间，并把值赋值给对象的属性。 -
NSString类型的属性推荐使用 copy，因为NSMutableString是NSString的子类，若将NSMutableString类型的对象赋值给NSString类型的属性，当对象变化时，属性值会发生改变，所以NSString推荐使用copy修饰。（面试重点😂） - 深拷贝、浅拷贝的区别在上面也有体现，浅拷贝是拷贝地址，深拷贝是拷贝值。
