“+”之间的区别和“ - ”在Objective-C中的函数名之前 [英] Difference between "+" and "-" before function name in Objective-C

问题描述

在Objective-C程序的函数名接口声明之前，+和 - 之间有什么区别。例子：

   - （void）continueSpeaking; 
 
 +（NSArray *）availableVoices; 
  

有什么区别？

解决方法 定义了一个类方法

类方法属于类本身，而不是实例。

示例： [AppDelegate someMethod]
$ - 定义一个实例方法

示例 [[[UIApplication sharedApplication] delegate] someMethod]

描述差异的一种方法是 - 方法对对象操作，而 + 方法对类本身进行操作。

假定你的类被命名为 MyClass ，并且你创建了它的一个实例并将它存储到一个名为 myInstance ：
$ b - （void）continueSpeaking 可以这样调用： [myInstance但是，方法 +（NSArray *）avai

lableVoices 只能这样调用： [MyClass availableVoices]

What is the difference between "+" and "-" before the function name interface declaration in an Objective-C program. Example:

- (void)continueSpeaking;

+ (NSArray *)availableVoices;

What's the difference?

解决方案

+ defines a class method

Class methods belong to the class itself, not instances of the class.

Example: [AppDelegate someMethod]

- defines an instance method

Example [[[UIApplication sharedApplication] delegate] someMethod]

One way to describe the difference is that - methods operate on objects, while + methods operate on the class itself.

Say your class was named MyClass, and you created an instance of it and stored it into a variable called myInstance:

- (void)continueSpeaking can be called like so: [myInstance continueSpeaking].

However, the method + (NSArray *)availableVoices can only be called like so: [MyClass availableVoices]

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