Qt 单例模式：本身就提供了专门的宏 Q_GLOBAL_STATIC 通过这个宏不但定义简单，还可以获得线程安全性

单例模式

很多人洋洋洒洒写了一大堆

但是Qt本身就提供了专门的宏 Q_GLOBAL_STATIC

通过这个宏不但定义简单，还可以获得线程安全性。

rule.h

#ifndef RULE_H
#define RULE_H

class Rule
{
public:
    static Rule* instance();
};

#endif // RULE_H

rule.cpp

#include "rule.h"

Q_GLOBAL_STATIC(Rule, rule)

Rule* Rule::instance()
{
    return rule();
}

写法很简单，用法也很简单

在任何地方，引用头文件 include "rule.h"

就可以 Rule::instance()->xxxxxx()

---

抽象工厂模式

主要是利用 Q_INVOKABLE 和 QMetaObject::newInstance

比如说你有一个Card类 card.h 和 2个派生的类

class Card : public QObject
{
   Q_OBJECT
public:
   explicit Card();
};
class CentaurWarrunner : public Card
{
   Q_OBJECT
public:
   Q_INVOKABLE CentaurWarrunner();
};
class KeeperoftheLight : public Card
{
   Q_OBJECT
public:
   Q_INVOKABLE KeeperoftheLight();
};

然后你写一个 engine.h 和 engine.cpp

#ifndef ENGINE_H
#define ENGINE_H

#include <QHash>
#include <QList>
#include <QMetaObject>

class Card;

class Engine
{
public:
    static Engine* instance();
    void loadAllCards();
    Card* cloneCard(int ISDN);

private:
    QHash<int, const QMetaObject*> metaobjects;
    QList<Card*> allcards;
};

#endif // ENGINE_H

#include "engine.h"
#include "card.h"

Q_GLOBAL_STATIC(Engine, engine)

Engine* Engine::instance()
{
   return engine();
}

void Engine::loadAllCards()
{
   allcards << new CentaurWarrunner()
            << new KeeperoftheLight();
   for (Card* card : allcards)
   {
       metaobjects.insert(card->getISDN(), card->metaObject());
   }
}

Card* Engine::cloneCard(int ISDN)
{
   const QMetaObject* meta = metaobjects.value(ISDN);
   if(meta == nullptr)
   {
       return nullptr;
   }
   return qobject_cast<Card*>(meta->newInstance());
}

这时，你就可以在其他cpp里通过 Card* card = Engine::instance()->cloneCard(ISDN);

从不同的int值得到不同的Card类型的对象