Question

我想实现一个抽象工厂模式，但也希望成为一个单例。

class WindowFactory {
protected:
    virtual Scrollbar* createScrollbar() = 0;
};

class MacWindowFactory: public WindowFactory {
    virtual Scrollbar* createScrollbar() {
        //return a instance
    }
    ;
};

class LinuxWindowFactory: public WindowFactory {
    virtual ScrollBar* createScrollbar() {
        //return a instance
    }
    ;
};

有人可以帮我提供一些制作这个抽象工厂单身的示例代码吗？

提前致谢。

Answer 1

我设法提出了更优雅的解决方案（截至目前没有错误检查）。请让我知道你的想法

#include<iostream>
#include<map>

class AbstractFactory
{
private:
    typedef std::map< std::string, AbstractFactory* > ClientMap;
    static ClientMap s_clientMap;
public:
    void virtual createScrollbar() = 0;
    void virtual createWindow() = 0;
    static AbstractFactory* createInstance( std::string client );
protected:
    void Register( std::string, AbstractFactory* );
};

AbstractFactory::ClientMap AbstractFactory::s_clientMap;

class LinuxFactory: public AbstractFactory
{
public:
    void createScrollbar()
    {
        std::cout<<"Scrollbar for Linux"<<std::endl;
    }

    void createWindow()
    {
        std::cout<<"WIndow for Linux"<<std::endl;
    }
private:
    LinuxFactory()
    {
        Register( "Linux", this );
    }
    LinuxFactory( const LinuxFactory& );
    static LinuxFactory s_LinuxFactory;

};
LinuxFactory LinuxFactory::s_LinuxFactory;

class MacFactory: public AbstractFactory
{
public:
    void createScrollbar()
    {
        std::cout<<"Scrollbar for Mac"<<std::endl;
    }

    void createWindow()
    {
        std::cout<<"WIndow for Mac"<<std::endl;
    }

private:
    MacFactory()
    {
        Register( "Mac", this );
    }
    MacFactory( const MacFactory& );
    static MacFactory s_MacFactory;
};
MacFactory MacFactory::s_MacFactory;

void AbstractFactory::Register( std::string clientName, AbstractFactory* factory )
{
    s_clientMap.insert( ClientMap::value_type( clientName, factory ) );

}
AbstractFactory* AbstractFactory::createInstance( std::string client )
{
return s_clientMap.find( client )->second;

}

int main()
{
AbstractFactory *factory = AbstractFactory::createInstance( "Linux" );
factory->createScrollbar();
factory->createWindow();
}

Answer 2

如果你需要一个实际动态的抽象工厂，你需要以某种方式在运行时设置它。您可以通过选择具有合适功能的所需工厂的功能来设置实际单例。在实际的应用程序中，您可能会有某种注册功能，您可以在其中注册获取工厂实例的功能（工厂工厂功能）。在下面的例子中，我使用了一个简单的设置，在编译时可以知道可用的工厂。

#include <memory>
#include <stdexcept>
#include <string>

class Scrollbar;

class WindowFactory {
public:
    static void setFactory(std::string const&);
    static Scrollbar* createScrollbar();
    virtual ~WindowFactory() {}

private:
    virtual Scrollbar* doCreateScrollbar() = 0;
};

class MacWindowFactory
    : public WindowFactory {
    friend void WindowFactory::setFactory(std::string const&);
    virtual Scrollbar* doCreateScrollbar() {
        return 0;
    }
};

class LinuxWindowFactory
    : public WindowFactory {
    friend void WindowFactory::setFactory(std::string const&);
    virtual Scrollbar* doCreateScrollbar() {
        return 0;
    }
};

// in WindowFactory.cpp

static std::auto_ptr<WindowFactory>& getPointer()
{
    static std::auto_ptr<WindowFactory> pointer;
    return pointer;
}

Scrollbar* WindowFactory::createScrollbar()
{
    return getPointer().get()
        ? getPointer()->doCreateScrollbar()
        : throw std::runtime_error("WindowFactory not set");
}

void WindowFactory::setFactory(std::string const& what)
{
    if (what == "Mac") {
        getPointer() = std::auto_ptr<WindowFactory>(new MacWindowFactory());
    }
    else if (what == "Linux") {
        getPointer() = std::auto_ptr<WindowFactory>(new LinuxWindowFactory());
    }
    else {
        throw std::runtime_error("unknown factory: '" + what + "'");
    }
}

Answer 3

namespace WindowFactory {
      Scrollbar* createScrollbar() {
        #ifdef TARGET_OS_MAC 
         ...
        #elif __linux__ 
         ...
        #endif
      }
};

我就是这样做的。

单身人士抽象工厂模式

3 个答案: