类方法和实例方法有什么区别? [英] What is the difference between class and instance methods?

问题描述

类方法和实例方法有什么区别?

What's the difference between a class method and an instance method?

实例方法是访问器(getter 和 setter)，而类方法几乎是其他所有东西吗?

Are instance methods the accessors (getters and setters) while class methods are pretty much everything else?

推荐答案

就像大多数其他答案所说的那样，实例方法使用类的实例，而类方法可以只使用类名.在 Objective-C 中，它们是这样定义的:

Like most of the other answers have said, instance methods use an instance of a class, whereas a class method can be used with just the class name. In Objective-C they are defined thusly:

@interface MyClass : NSObject

+ (void)aClassMethod;
- (void)anInstanceMethod;

@end

然后可以像这样使用它们:

They could then be used like so:

[MyClass aClassMethod];

MyClass *object = [[MyClass alloc] init];
[object anInstanceMethod];

类方法的一些真实示例是许多基础类中的便捷方法，例如 NSString 的 +stringWithFormat: 或 NSArray 的+arrayWithArray:.一个实例方法是 NSArray 的 -count 方法.

Some real world examples of class methods are the convenience methods on many Foundation classes like NSString's +stringWithFormat: or NSArray's +arrayWithArray:. An instance method would be NSArray's -count method.

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