NSString属性何时用strong何时用copy？

前言

我们在声明一个nsstring属性时，对于其内存相关特性，通常有两种选择(基于arc环境)：strong与copy。那这两者有什么区别呢？什么时候该用strong，什么时候该用copy呢？让我们先来看个例子。

代码验证

@property (nonatomic, strong) nsstring *mystrongstring;

@property (nonatomic, copy) nsstring *mycopystring;

- (void)stringtest {

nsmutablestring *mutablestr = [nsmutablestring stringwithformat:@"https://"];

self.mystrongstring = mutablestr;

self.mycopystring = mutablestr;

nslog(@"mutablestr:%p,%p", mutablestr,&mutablestr);

nslog(@"strongstring:%p,%p", _mystrongstring, &_mystrongstring);

nslog(@"copystring:%p,%p", _mycopystring, &_mycopystring);

//---------------分割线---------------------

[mutablestr appendstring:@"devthinking.com"];

nslog(@"strongstring:%p,%p", _mystrongstring, &_mystrongstring);

nslog(@"copystring:%p,%p", _mycopystring, &_mycopystring);

}

打印日志如下：