Qt代码举例-单例模式

使用Qt方便的实现单例模式

单例类的实现，其中qCallOnce函数是确保该函数只执行一次：

#ifndef SINGLETON
#define SINGLETON

#include <QtGlobal>
#include <QScopedPointer>
#include "call_once.h"

template <class T>
class Singleton
{
public:
    static T& instance()
    {
        qCallOnce(init, flag);
        return *tptr;
    }

    static void init()
    {
        tptr.reset(new T);
    }

private:
    Singleton() {}
    ~Singleton() {}
    Q_DISABLE_COPY(Singleton)

    static QScopedPointer<T> tptr;
    static QBasicAtomicInt flag;
};

template<class T> QScopedPointer<T> Singleton<T>::tptr(0);
template<class T> QBasicAtomicInt Singleton<T>::flag = Q_BASIC_ATOMIC_INITIALIZER(CallOnce::CO_Request);

#endif // SINGLETON

使用举例：

class TestClass : public QObject
{
};
#define TestClassInstance Singleton<TestClass >::instance()

 还有一种更简单的：

#include <QMutexLocker>

class TestClass
{
public:
    inline static TestClass* nstance()
    {
        QMutexLocker locker(&mutex);
        if (NULL == m_instance)
        {
            m_instance = new TestClass();
        }
        return m_instance;
    }
    
private:
    static QMutex mutex;
    static TestClass* m_instance;
};