如何从NSMutableString取出NSString？ [英] How to take an NSString out of an NSMutableString?

问题描述

这有点混乱。 NSMutableString继承自NSString，但是这也意味着我可以在任何地方安全地传递一个NSMutableString，而实际上是一个NSString。我可以分配NSString到NSMutableString吗？

That's somewhat confusing. NSMutableString inherits from NSString, but does that also mean that I can pass an NSMutableString anywhere safely where actually an NSString is wanted? And can I assign an NSString to an NSMutableString? How would I get an NSString out of an NSMutableString to avoid problems, if any?

推荐答案

1. 如果有NSString从NSMutableString中获取NSString， p>是的，您可以为 NSString 传递 NSMutableString 。但是，请注意，如果传递给它的对象存储对此对象的引用，它将看到您对可变字符串对象所做的所有更改。

1. Yes, you can pass an NSMutableString for an NSString. However, be aware that if the object you pass it to stores a reference to this object, it will "see" all the changes you make to the mutable string object. This is not always desirable.

不，不可能。如果你有一个 NSMutableString 指针指向 NSString 并调用，例如， appendString： / code>，对象不知道如何处理调用。

No, not possible. If you had a NSMutableString pointer pointing to an NSString and called, say, appendString: on it, the object wouldn't know how to process the call.

（前两个是OO包含多态性基础）

(the first two are OO inclusion polymorphism basics)

如果要从可变变量字符串中获取不可变字符串，请使用 [mutableString copy] p>

If you want to get a non-mutable string from a mutable one, use [mutableString copy].

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