使用函数指针来代替switch语句

使用函数指针来代替
Switch

语句【以下是公司项目中部分的
videoSwitchAgent

】



使用一个单件的工程，将要创建的实体用不同的函数来表示，在这个工厂里面用一个
map
来保存所有创建实体的方法。由于
map
是可以链表结构没有大小限制，这样就可以做到便于扩充。

 

代码如下：

// EntityCreationFactory.h

namespace TA_IRS_App

{

    class EntityCreationFactory

    {

    public:

        typedef TA_Base_Bus::IEntity* ( *CreatorFunction )( TA_Base_Core::IEntityDataPtr entityData );

    static EntityCreationFactory& getInstance();

        void registerFunction( const std::string& type, CreatorFunction function );

        TA_Base_Bus::IEntity* createEntity( TA_Base_Core::IEntityDataPtr entityData );

    private:

        EntityCreationFactory();

        virtual ~EntityCreationFactory() {};

        EntityCreationFactory( const EntityCreationFactory& theEntityCreationFactory );

        EntityCreationFactory& operator=( const EntityCreationFactory& theEntityCreationFactory );

    static TA_Base_Bus::IEntity* createCamera( TA_Base_Core::IEntityDataPtr entityData );

        static TA_Base_Bus::IEntity* createVideoMonitor( TA_Base_Core::IEntityDataPtr entityData );

        static TA_Base_Bus::IEntity* createVideoOutputGroup( TA_Base_Core::IEntityDataPtr entityData );

        static TA_Base_Bus::IEntity* createQuad( TA_Base_Core::IEntityDataPtr entityData );

        static TA_Base_Bus::IEntity* createBVSStage( TA_Base_Core::IEntityDataPtr entityData );

        static TA_Base_Bus::IEntity* createSequence( TA_Base_Core::IEntityDataPtr entityData );

        static TA_Base_Bus::IEntity* createRecordingUnit( TA_Base_Core::IEntityDataPtr entityData );

    typedef std::map< std::string, CreatorFunction > FunctionMap;

        FunctionMap m_functions;

    static EntityCreationFactory*    s_singleton;

    static TA_Base_Core::ReEntrantThreadLockable    s_singletonLock

    }; // EntityCreationFactory

} // TA_IRS_App

//EntityCreeationFactory.cpp

namespace TA_IRS_App

{

    EntityCreationFactory* EntityCreationFactory::s_singleton = NULL;

    TA_Base_Core::ReEntrantThreadLockable EntityCreationFactory::s_singletonLock;

    EntityCreationFactory& EntityCreationFactory::getInstance()

    {

        if ( s_singleton == NULL )

        {

            TA_Base_Core::ThreadGuard guard( s_singletonLock );

            if ( s_singleton == NULL )

            {

                s_singleton = new EntityCreationFactory();

            }

        }

        return *s_singleton;

  }

    EntityCreationFactory::EntityCreationFactory()

    {

        registerFunction( TA_Base_Core::Camera::getStaticType(), createCamera );

        registerFunction( TA_Base_Core::VideoMonitor::getStaticType(), createVideoMonitor );

        registerFunction( TA_Base_Core::VideoOutputGroup::getStaticType(), createVideoOutputGroup );

        registerFunction( TA_Base_Core::Quad::getStaticType(), createQuad );

        registerFunction( TA_Base_Core::BVSStage::getStaticType(), createBVSStage );

        registerFunction( TA_Base_Core::Sequence::getStaticType(), createSequence );

        registerFunction( TA_Base_Core::RecordingUnit::getStaticType(), createRecordingUnit );

    }

    void EntityCreationFactory::registerFunction( const std::string& type, CreatorFunction function )

    {

        TA_ASSERT( m_functions.end() == m_functions.find( type ),

            "A function is already registered for this type." );

        m_functions[ type ] = function;

    }

    TA_Base_Bus::IEntity* EntityCreationFactory::createEntity( TA_Base_Core::IEntityDataPtr entityData )

    {

        std::string type = entityData->getType();

       

        LOG_GENERIC(SourceInfo, TA_Base_Core::DebugUtil::DebugInfo, "the type is %s", type.c_str());

        FunctionMap::iterator it = m_functions.find( type );

        if ( m_functions.end() == it )

        {

            LOG_GENERIC( SourceInfo, TA_Base_Core::DebugUtil::DebugInfo,

                "Entity could not be created because it is of an unrecognised type: %s", type.c_str() );

            return 0;

        }

        return it->second( entityData );

    }

    // Private methods

    TA_Base_Bus::IEntity* EntityCreationFactory::createCamera( TA_Base_Core::IEntityDataPtr entityData )

    {

        TA_Base_Bus::IEntity *pResult = NULL;

        return pResult;

    }

    // Private methods

    TA_Base_Bus::IEntity* EntityCreationFactory::createCamera( TA_Base_Core::IEntityDataPtr entityData )

    {

        TA_Base_Bus::IEntity *pResult = NULL;

        return pResult;

    }

} // end TA_IRS_App

// client

TA_Base_Bus::IEntity *pEntity = EntityAccessFactory::getInstance().createEntity();