设计模式（九）————外观模式（Facade Pattern）

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本文深入解析了外观模式的设计理念，通过C++和C#两种语言的实际代码，展示了如何创建统一的接口来简化子系统的访问。通过Shape抽象类及其派生类Circle、Sphere和Cube的具体实现，配合Context类的使用，清晰地说明了外观模式的应用场景和优势。

定义：定义一个统一的接口，用来访问子系统中的一群接口。外观定义了一个高层接口，让子系统更容易使用。

UML类图：

C++实现：

#include<iostream>
using namespace std;

class Shape
{
	virtual void Draw() = 0;
public:
	virtual ~Shape() = default;
};
class Circle :public Shape
{
public:
	// 通过 Shape 继承
	virtual void Draw() override
	{
		cout << "Draw Circle!" << endl;
	}
	virtual ~Circle() {}
};
class Sphere :public Shape
{
public:
	// 通过 Shape 继承
	virtual void Draw() override
	{
		cout << "Draw Sphere!" << endl;
	}
	virtual ~Sphere() {}
};
class Cube :public Shape
{
public:
	// 通过 Shape 继承
	virtual void Draw() override
	{
		cout << "Draw Cube!" << endl;
	}
	virtual ~Cube() {}
};
class Context
{
	Circle* circle;
	Sphere* sphere;
	Cube* cube;

public:
	Context()
	{
		circle = new Circle();
		sphere = new Sphere();
		cube = new Cube();
	}
	void DrawCircle()
	{
		circle->Draw();
	}
	void DrawSphere()
	{
		sphere->Draw();
	}
	void DrawCube()
	{
		cube->Draw();
	}
	~Context()
	{
		delete circle;
		delete sphere;
		delete cube;
	}
};
int main()
{
	Context* context = new Context();
	context->DrawCircle();
	context->DrawSphere();
	context->DrawCube();
	delete context;
	return 0;
}

C#实现：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml;
using static System.Console;

namespace ConsoleApp1
{

    public interface Shape
    {
        void Draw();
    }
    public class Circle:Shape
    {
        public void Draw()
        {
            WriteLine("Draw Circle!");
        }
    }
    public class Sphere : Shape
    {
        public void Draw()
        {
            WriteLine("Draw Sphere!");
        }
    }
    public class Cube : Shape
    {
        public void Draw()
        {
            WriteLine("Draw Cube!");
        }
    }
    public class Context
    {
       private Circle circle;
       private Sphere sphere;
       private Cube cube;

       public Context()
       {
            circle = new Circle();
            sphere = new Sphere();
            cube = new Cube();
       }

       public void DrawCircle()
       {
            circle.Draw();
       }
       public void DrawSphere()
       {
            sphere.Draw();
       }
       public void DrawCube()
       {
            cube.Draw();
       }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Context context = new Context();
            context.DrawCircle();
            context.DrawCube();
            context.DrawSphere();
        }
    }
}