设计模式-门面 2022-02-23

门面模式(Facade Pattern)是一种结构型设计模式，能为程序库、框架或其他复杂类提供一个简单的接口。

门面模式 UML

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适用场景

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1. 如果你需要一个指向复杂子系统的直接接口，且该接口的功能有限，则可以使用外观模式
2. 如果需要将子系统组织为多层结构，可以使用外观

代码示例

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using System;
namespace FacadePatternDemo 
{
    public class Facade
    {
        protected Subsystem1 _subsystem1;
        
        protected Subsystem2 _subsystem2;

        public Facade(Subsystem1 subsystem1, Subsystem2 subsystem2)
        {
            this._subsystem1 = subsystem1;
            this._subsystem2 = subsystem2;
        }
        
        public string Operation()
        {
            string result = "Facade initializes subsystems:\n";
            result += this._subsystem1.operation1();
            result += this._subsystem2.operation1();
            result += "Facade orders subsystems to perform the action:\n";
            result += this._subsystem1.operationN();
            result += this._subsystem2.operationZ();
            return result;
        }
    }
    
    public class Subsystem1
    {
        public string operation1()
        {
            return "Subsystem1: Ready!\n";
        }

        public string operationN()
        {
            return "Subsystem1: Go!\n";
        }
    }
    
    public class Subsystem2
    {
        public string operation1()
        {
            return "Subsystem2: Get ready!\n";
        }

        public string operationZ()
        {
            return "Subsystem2: Fire!\n";
        }
    }

    class Client
    {
        public static void ClientCode(Facade facade)
        {
            Console.Write(facade.Operation());
        }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            Subsystem1 subsystem1 = new Subsystem1();
            Subsystem2 subsystem2 = new Subsystem2();
            Facade facade = new Facade(subsystem1, subsystem2);
            Client.ClientCode(facade);
            // output

            // Facade initializes subsystems:
            // Subsystem1: Ready!
            // Subsystem2: Get ready!
            // Facade orders subsystems to perform the action:
            // Subsystem1: Go!
            // Subsystem2: Fire!
        }
    }
}