工程結構：

原始碼：

-----------------PluginPerson.pro---------------

TEMPLATE = subdirs

SUBDIRS += xiaoming \
    person

-----------------person.pro-------------------

#-------------------------------------------------
#
# Project created by QtCreator 2015-07-27T11:41:44
#
#-------------------------------------------------

QT       += core
QT       -= gui

DESTDIR = ../../PluginPerson/exe

TARGET = person
CONFIG   += console
CONFIG   -= app_bundle

TEMPLATE = app

SOURCES += main.cpp

HEADERS += \
    personinterface.h
 

---------------personinterface.h-----------------

#ifndef PERSONINTERFACE_H
#define PERSONINTERFACE_H

#include <QString>
#include <QtPlugin>

#define PersonInterface_IID "org.qt-project.Qt.Person"

class PersonInterface
{
public:
    virtual QString name()=0;
    virtual int age()=0;
    virtual void sing()=0;
};

Q_DECLARE_INTERFACE(PersonInterface, PersonInterface_IID)

#endif // PERSONINTERFACE_H
 

------------main.cpp------------

#include <QCoreApplication>
#include <QDebug>

#include <QPluginLoader>
#include <QFile>

#include "../person/personinterface.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    qDebug()<<"person....";

    QPluginLoader loader(QCoreApplication::applicationDirPath().append("/xiaoming.dll"));

    QObject *obj=qobject_cast<QObject *>(loader.instance());
    if(obj){
        PersonInterface *person=qobject_cast<PersonInterface *>(obj);
        if(person){
            qDebug()<<"load success!";
            qDebug()<<"name="<<person->name()<<", age="<<person->age();
            person->sing();
        }else{
            qDebug()<<"person error!";
        }
    }else{
        qDebug()<<"object error!";
    }

    return 0;
}
 

-----------------xiaoming.pro-----------------

#-------------------------------------------------
#
# Project created by QtCreator 2015-07-27T14:05:56
#
#-------------------------------------------------

QT       -= gui

TARGET = xiaoming
TEMPLATE = lib

DESTDIR = ../../PluginPerson/exe

SOURCES += xiaoming.cpp

HEADERS += xiaoming.h

unix {
    target.path = /usr/lib
    INSTALLS += target
}

OTHER_FILES += \
    Person.json

----------------xiaoming.h------------------

#ifndef XIAOMING_H
#define XIAOMING_H

#include "../person/personinterface.h"

class Xiaoming : public QObject, PersonInterface
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID PersonInterface_IID FILE "Person.json")
    Q_INTERFACES(PersonInterface)
public:
    QString name();
    int age();
    void sing();
};

#endif // XIAOMING_H

---------------xiaoming.cpp--------------

#include "xiaoming.h"

#include <QDebug>

QString Xiaoming::name()
{
    return "xiaoming";
}

int Xiaoming::age()
{
    return 10;
}

void Xiaoming::sing()
{
    qDebug()<<"xiaoming sing ...";
}

--------------Person.json是一個空檔案--------------

執行效果：

 附：

下面是Qt官方文件上的一個例子

class FilterInterface
{
public:
    virtual ~FilterInterface() {}

    virtual QStringList filters() const = 0;
    virtual QImage filterImage(const QString &filter, const QImage &image,
                               QWidget *parent) = 0;
};

#include <QObject>
#include <QtPlugin>
#include <QStringList>
#include <QImage>

#include <plugandpaint/interfaces.h>

class ExtraFiltersPlugin : public QObject, public FilterInterface
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.Examples.PlugAndPaint.FilterInterface" FILE "extrafilters.json")
    Q_INTERFACES(FilterInterface)

public:
    QStringList filters() const;
    QImage filterImage(const QString &filter, const QImage &image,
                       QWidget *parent);
};

注意：經過測試，在Qt5中Q_PLUGIN_METADATA這一行是必須有的，否則外掛會載入不上。

（-----------完---------）