设计模式总结 通过命令模式

注：

文档内容基本上来自于网上，并加上自己的理解而成。有的觉得网友总结得非常好，就完全照搬下来，供学习之用。然而，有的摘抄并没有加上原链接和出处，请谅解。

通过命令模式，通过在客户端和具体的命令之间添加一层Invoker，剪断了客户端和具体服务提供者之间的耦合，降低了两者之间的耦合度，同时也增加了灵活性，比如我们可以灵活的某一个请求的服务提供者，通过单独的服务提供者Command类，可以很方便的提供redo和undo的功能等等，这些都是命令模式的优势。

在软件系统中，“行为请求者”与“行为实现者”通常呈现一种“紧耦合”。但在某些场合，比如要对行为进行“记录、撤销/重做、事务”等处理，这种无法抵御变化的紧耦合是不合适的。在这种情况下，如何将“行为请求者”与“行为实现者”解耦？将一组行为抽象为对象，实现二者之间的松耦合。这就是命令模式（Command Pattern）

即命令模式的核心是要解决“行为请求者”和“行为实现”都之间的耦合，以达到灵活多变的效果。

目标：

客户只需要发命令，而不需要管命令是如何被执行的！Command pattern

From Wikipedia,the free encyclopedia

In object-oriented programming,the command pattern is

the method and values for the method parameters.

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[edit]Uses

[edit]Structure

UPDATE:The explanation for the Receiver block above should be

"The actual work to be done by the command(action)"

[edit]Terminology

1.Ambiguity.

2.The term command is

ambiguous.For

example,move up,move

up may refer to a single

5.Client,Source,Invoker:the

button,toolbar button,or

menu item clicked,the

shortcut key pressed by the

user.

mand Object,Routed

Command Object,Action

Object:a singleton object

(e.g.there is only one

CopyCommand object),

which knows about shortcut

keys,button images,

command text,etc.related

to the command.A

source/invoker object calls

the Command/Action

object's

execute/performAction

method.The

Command/Action object

notifies the appropriate

source/invoker objects

when the availability of a

command/action has

changed.This allows

buttons and menu items to

become inactive(grayed out) when a command/action

cannot be

executed/performed.

7.Receiver,Target Object:

the object that is about to

be copied,pasted,moved,

etc.The receiver object

owns the method that is

called by the

command's execute method.

The receiver is typically also

the target object.For

example,if the receiver object is a cursor and the method is called moveUp,

then one would expect that

the cursor is the target of

the moveUp action.On the

other hand,if the code is

defined by the command

object itself,the target

object will be a different

object entirely.

mand Object,routed

event args,event object:

the object that is passed

from the source to the

Command/Action object,to

the Target object to the

code that does the work.

Each button click or

shortcut key results in a new

command/event object.