在 Ruby 中调用另一个类中的类中的方法
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Call a method in a class in another class in Ruby
提问by Pabi
I was wondering how I could call a method in an instance of a class in another class.
我想知道如何在另一个类的类的实例中调用方法。
This is what I came up with
这是我想出的
class ClassA
def method
return "This is a method_from_class_A"
end
end
class ClassB
def initialize
@method_from_class_A=instance.method
end
def method_calls_method
@method_from_class_A
end
end
instance=ClassA.new
instance2=ClassB.new
puts instance2.method_calls_method
But I get this error:
但我收到此错误：
Testing.rb:9:in
initialize': undefined local variable or methodinstance' for # (NameError) from Testing.rb:19:innew' from Testing.rb:19:in'
Testing.rb:9:in
initialize': undefined local variable or methodinstance' for # (NameError) from Testing.rb:19:innew' from Testing.rb:19:in'
How could I fix it?
我怎么能修好呢？
Thank you for your response.
谢谢您的答复。
采纳答案by Mori
From your description this seems to be what you're going for:
从你的描述来看，这似乎是你想要的：
class ClassB
def initialize
@instance_of_class_a = ClassA.new
end
def method_calls_method
@instance_of_class_a.method
end
end
Or to pass in the ClassAinstance (this is called dependency injection):
或者传入ClassA实例（这称为依赖注入）：
class ClassB
def initialize(class_a_instance)
@instance_of_class_a = class_a_instance
end
def method_calls_method
@instance_of_class_a.method
end
end
instance_a = ClassA.new
instance_b = ClassB.new(instance_a)
puts instance_b.method_calls_method
回答by timthez
Another Option would be to take a look at class methods: https://rubymonk.com/learning/books/4-ruby-primer-ascent/chapters/45-more-classes/lessons/113-class-variables
另一种选择是查看类方法：https: //rubymonk.com/learning/books/4-ruby-primer-ascent/chapters/45-more-classes/lessons/113-class-variables
So in your code it would look similar to this:
因此，在您的代码中，它看起来类似于：
class ClassA
def self.method
return "This is a method_from_class_A"
end
end
class ClassB
def method_calls_method
ClassA.method
end
end
instance=ClassB.new
puts instance.method_calls_method
*Notice the self.in ClassA to signify a class method. This is similar to a static method in other languages.
*注意self.ClassA 中的 表示类方法。这类似于其他语言中的静态方法。
According to wikipedia: https://en.wikipedia.org/wiki/Method_(computer_programming)#Static_methods
根据维基百科：https://en.wikipedia.org/wiki/Method_(computer_programming)#Static_methods
Class(static) methods are meant to be relevant to all the instances of a class rather than to any specific instance.
类（静态）方法旨在与类的所有实例相关，而不是与任何特定实例相关。
You see class methods used a lot in the ruby Math class: http://ruby-doc.org/core-2.2.2/Math.html
您会看到 ruby Math 类中大量使用的类方法：http: //ruby-doc.org/core-2.2.2/Math.html
For example taking a square root of a number in is done by using the class method Math.sqrt. This is different from an instance method which would look like object.methodinstead Class.method. There are a lot of resources and tutorials out that explains this concept in more detail and probably clearer.
例如，使用类方法对 in 取一个数的平方根Math.sqrt。这是一个实例方法，它看起来像不同的object.method代替Class.method。有很多资源和教程更详细地解释了这个概念，可能更清楚。
