方法旁边的Objective-C中的正号和负号是什么意思? [英] What do the plus and minus signs mean in Objective-C next to a method?

问题描述

在Objective-C中，我想知道方法定义旁边的+和-符号是什么意思.

In Objective-C, I would like to know what the + and - signs next to a method definition mean.

- (void)loadPluginsAtPath:(NSString*)pluginPath errors:(NSArray **)errors;

推荐答案

+用于类方法，而-用于实例方法.

+ is for a class method and - is for an instance method.

例如

// Not actually Apple's code.
@interface NSArray : NSObject {
}
+ (NSArray *)array;
- (id)objectAtIndex:(NSUInteger)index;
@end

// somewhere else:

id myArray = [NSArray array];         // see how the message is sent to NSArray?
id obj = [myArray objectAtIndex:4];   // here the message is sent to myArray

// Btw, in production code one uses "NSArray *myArray" instead of only "id".

还有另一个有关类和实例方法之间差异的问题.

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