Design Pattern C # implementation (15)--Command mode

• • Intention
  • Applicability
  • Structure
  • Realize
  • Effect
  • Reference

Intention

Encapsulates the request as an object, the customer accepts the request parameters, can queue the request or logs the request log, and can support the undo operation

Applicability

• Abstract the action to be executed to parameterize an object. The command pattern is an object-oriented alternative to the callback mechanism.
• Specify, arrange, and execute requests at different times
• Support Cancel operation
• Support for modifying logs
• Support Transactions

Structure

Realize

Remote control of a lamp is realized by using the remote control. The lights are on and off with two operations.

  class  Light{Public   void on()         {Console.WriteLine (" Light was on"); }Public   void Off()         {Console.WriteLine ("Light is Off"); }    }

First, the Operation class or interface is abstracted.

   Public Interface ICommand{ void Execute() ; void Undo() ;//Revoke}

This opens, closes two operation requests to encapsulate, the operation needs an object as the initialization parameter

 class Lightoncommand:ICommand{PrivateLight _light;Public   lightoncommand(light)         { This. _light = Light; }Public   void Execute()         {_light.        On (); }Public   void Undo()         {_light.        Off (); }    }class Lightoffcommand:ICommand{PrivateLight _light;Public   lightoffcommand(light)         { This. _light = Light; }Public   void Execute()         {_light.        Off (); }Public   void Undo()         {_light.        On (); }    }

The remote control accepts the request as an initialization parameter

class Simpleremotecontrol{PrivateICommand _onslot;PrivateICommand _offslot;PrivateICommand _lastcommand;//Record last action request        Public   void setcommand(ICommand oncommand,icommand offcommand)         {_onslot = OnCommand;        _offslot = Offcommand; }Public   void onbuttonwaspressed()         {_onslot.execute ();        _lastcommand = _onslot; }Public   void offbuttonwaspressed()         {_offslot.execute ();        _lastcommand = _offslot; }Public   void Undo()         {_lastcommand.undo (); }    }

Parameterize the customer (remote control) with the encapsulated request, allowing the lamp to be controlled, or to encapsulate more operations so that the remote controls other items

 class  Program{ static void Main(string[] args)         {Simpleremotecontrol remote =NewSimpleremotecontrol (); Light light =NewLight (); Lightoncommand Lighton =NewLightoncommand (light); Lightoffcommand Lightoff =NewLightoffcommand (light); Remote.            SetCommand (Lighton, Lightoff); Remote.            Onbuttonwaspressed (); Remote.            Offbuttonwaspressed (); Remote. Undo ();//Undo Previous actionConsole.readkey (); }    }

Run results

Effect

• Decouple the object that invokes the operation from the object that knows how to implement the operation
• Multiple commands can be assembled into a composite command
• Add a new command without modifying an existing class

Reference

1. "Head First design mode"
2. "Design Mode"

Design Pattern C # implementation (15)--Command mode