我的Design Pattern之旅[6]：Adapter Pattern(OO)(7)

Example

在(原創) 我的Design Pattern之旅[1]：Strategy Pattern (OO) (Design Pattern) (C?C++) (template) (.NET) (C#)中Grapher使用了Strategy Pattern，為了可動態載入畫Triangle，畫Circle，畫Squre的算法，我們定了IDrawStrategy interface，並且寫了Triangle、Circle、Square三個class實現IDrawStrategy interface，但今天發現在某個framwork/library中(如.NET Framework中的GDI+或DirectX)，已經存在畫Triangle、Circle、Square的算法了，所以不需重新自己寫，但因為interface不同，所以Grapher無法使用，且我們又沒有該framework/library的source code，根本無法修改成實現IDrawStrategy interface(如我們根本沒有DirectX或.Net Framework的source code)，所以我們只好寫一個DrawAdapter，讓Grapher可以使用之。

Class Adapter

IDrawStrategy interface定的是draw()，但IPaint interface定的是paint()，所以Grapher無法使用，因為無法修改IPaint interface和Triangle class、Circle class、Square class(因為可能在其他Framework內，無source code可修改)，所以只好加上TriangleDrawAdapter，CircleDrawAdapter和SquareDrawAdapter做轉換。

ISO C++

/**//*
(C) OOMusou 2007 http://oomusou.cnblogs.com

Filename　　: DP_AdpaterPattern_Strategy_Class.cpp
Compiler　　: Visual C++ 8.0 / BCB 6.0 / gcc 3.4.2 / ISO C++
Description : Demo how to use Strategy Pattern with Adapter Pattern (Class).
Release　　 : 07/15/2007 1.0
*/
#include <iOStream>
using namespace std;

class IDrawStrategy {
public:
　virtual void draw() const = 0;
};

class Grapher {
public:
　Grapher(IDrawStrategy* drawStrategy = 0) : _drawStrategy(drawStrategy) {}

public:
　void drawShape() const;
　void setShape(IDrawStrategy* drawStrategy);

protected:
　IDrawStrategy* _drawStrategy;
};

void Grapher::drawShape() const {
　if (_drawStrategy)
　　　_drawStrategy->draw();
}

void Grapher::setShape(IDrawStrategy* drawStrategy) {
　_drawStrategy = drawStrategy;
}

class IPaint {
public:
　virtual void paint() const = 0;
};

class Triangle : public IPaint {
public:
　void paint() const;
};

void Triangle::paint() const {
　cout << "Draw Triangle" << endl;
}

class Circle : public IPaint {
public:
　void paint() const;
};

void Circle::paint() const {
　cout << "Draw Circle" << endl;
}

class Square : public IPaint {
public:
　void paint() const;
};

void Square::paint() const {
　cout << "Draw Square" << endl;
}

class TriangleDrawAdapter : public IDrawStrategy, private Triangle {
public:
　virtual void draw() const;
};

void TriangleDrawAdapter::draw() const {
　paint();
}

class CircleDrawAdapter : public IDrawStrategy, private Circle {
public:
　virtual void draw() const;
};

void CircleDrawAdapter::draw() const {
　paint();
}

class SquareDrawAdapter : public IDrawStrategy, private Square {
public:
　virtual void draw() const;
};

void SquareDrawAdapter::draw() const {
　paint();
}

int main() {
　Grapher grapher(&TriangleDrawAdapter());
　grapher.drawShape();

　grapher.setShape(&CircleDrawAdapter());
　grapher.drawShape();

　grapher.setShape(&SquareDrawAdapter());
　grapher.drawShape();
}