复制vs强大的属性 [英] copy vs strong properties

问题描述

我在iOS中比较新鲜，我想知道我们应该在属性中使用 copy ，例如

I am fresher in iOS and I want to know that when we should use copy in a property, e.g.

@property (nonatomic, retain) NSString* name;

vs

@property (nonatomic, copy) NSString* name;`

有什么区别保留和复制，我何时应该使用一个而不是另一个？

What is the difference between retain and copy, and when should I use one but not the other?

推荐答案

@property (nonatomic, copy) NSString* name;

更好，因为 NSString 是不可变的，它的子类 NSMutableString 是可变的。

is better, as NSString is immutable and it's child class NSMutableString is mutable.

只要您使用 NSString 通过，你不会看到任何差异。但是当你开始使用 NSMutableString 时，事情就会变得有点冒险。

As long as you are using NSString through out, you won't see any difference. But when you start using NSMutableString, things can get little dicey.

NSMutableString *department = [[NSMutableString alloc] initWithString:@"Maths"];

Person *p1 = [Person new];
p1.department = department;

//Here If I play with department then it's not going to affect p1 as the property was copy
//e.g.
[department appendString:@"You're in English dept."];

如果它只是保留它会改变部门的p1 。
因此，在这种情况下，优先考虑复制。

Had it been just retain it would have changed the department of the p1. So having copy is prefered in this case.

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