Ruby 命令模式讲解和代码示例
命令是一种行为设计模式， 它可将请求或简单操作转换为一个对象。
此类转换让你能够延迟进行或远程执行请求， 还可将其放入队列中。
复杂度：
流行度：
使用示例： 命令模式在 Ruby 代码中很常见。 大部分情况下， 它被用于代替包含行为的参数化 UI 元素的回调函数， 此外还被用于对任务进行排序和记录操作历史记录等。
识别方法： 命令模式可以通过抽象或接口类型 （发送者） 中的行为方法来识别， 该类型调用另一个不同的抽象或接口类型 （接收者） 实现中的方法， 该实现则是在创建时由命令模式的实现封装。 命令类通常仅限于一些特殊行为。
概念示例
本例说明了命令设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
main.rb: 概念示例
# The Command interface declares a method for executing a command.
class Command
# @abstract
def execute
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
end
# Some commands can implement simple operations on their own.
class SimpleCommand < Command
# @param [String] payload
def initialize(payload)
@payload = payload
end
def execute
puts "SimpleCommand: See, I can do simple things like printing (#{@payload})"
end
end
# However, some commands can delegate more complex operations to other objects,
# called "receivers".
class ComplexCommand < Command
# Complex commands can accept one or several receiver objects along with any
# context data via the constructor.
def initialize(receiver, a, b)
@receiver = receiver
@a = a
@b = b
end
# Commands can delegate to any methods of a receiver.
def execute
print 'ComplexCommand: Complex stuff should be done by a receiver object'
@receiver.do_something(@a)
@receiver.do_something_else(@b)
end
end
# The Receiver classes contain some important business logic. They know how to
# perform all kinds of operations, associated with carrying out a request. In
# fact, any class may serve as a Receiver.
class Receiver
# @param [String] a
def do_something(a)
print "\nReceiver: Working on (#{a}.)"
end
# @param [String] b
def do_something_else(b)
print "\nReceiver: Also working on (#{b}.)"
end
end
# The Invoker is associated with one or several commands. It sends a request to
# the command.
class Invoker
# Initialize commands.
# @param [Command] command
def on_start=(command)
@on_start = command
end
# @param [Command] command
def on_finish=(command)
@on_finish = command
end
# The Invoker does not depend on concrete command or receiver classes. The
# Invoker passes a request to a receiver indirectly, by executing a command.
def do_something_important
puts 'Invoker: Does anybody want something done before I begin?'
@on_start.execute if @on_start.is_a? Command
puts 'Invoker: ...doing something really important...'
puts 'Invoker: Does anybody want something done after I finish?'
@on_finish.execute if @on_finish.is_a? Command
end
end
# The client code can parameterize an invoker with any commands.
invoker = Invoker.new
invoker.on_start = SimpleCommand.new('Say Hi!')
receiver = Receiver.new
invoker.on_finish = ComplexCommand.new(receiver, 'Send email', 'Save report')
invoker.do_something_important
output.txt: 执行结果
Invoker: Does anybody want something done before I begin?
SimpleCommand: See, I can do simple things like printing (Say Hi!)
Invoker: ...doing something really important...
Invoker: Does anybody want something done after I finish?
ComplexCommand: Complex stuff should be done by a receiver object
Receiver: Working on (Send email.)
Receiver: Also working on (Save report.)
