Qt 出現“undefined reference to `vtable for”原因總結

今天寫了Qt內建的Demo的一個執行個體，總是會出現undefined reference to `vtable for的錯誤，查了一些網上的資料終於知道哪裡出錯了，自己做個記載，直接放上代碼，代碼中間注釋說明了錯誤的原因

#include <QtCore>#include <QtGui>class Pixmap : public QGraphicsWidget{    Q_OBJECTpublic:    Pixmap(const QPixmap &pix, QGraphicsItem *parent = 0)        : QGraphicsWidget(parent), orig(pix), p(pix)    {    }    void paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)    {        painter->drawPixmap(QPointF(), p);    }    virtual void mousePressEvent(QGraphicsSceneMouseEvent * )    {        emit clicked();    }    virtual void setGeometry(const QRectF &rect)    {        QGraphicsWidget::setGeometry(rect);        if (rect.size().width() > orig.size().width())            p = orig.scaled(rect.size().toSize());        else            p = orig;    }Q_SIGNALS:    void clicked();private:    QPixmap orig;    QPixmap p;};class GraphicsView : public QGraphicsView{    Q_OBJECTpublic:    GraphicsView(QGraphicsScene *scene, QWidget *parent = 0) : QGraphicsView(scene, parent)    {    }    virtual void resizeEvent(QResizeEvent *event)    {        fitInView(sceneRect(), Qt::KeepAspectRatio);    }};void createStates(const QObjectList &objects,                  const QRect &selectedRect, QState *parent){    for (int i = 0; i < objects.size(); ++i) {        QState *state = new QState(parent);        state->assignProperty(objects.at(i), "geometry", selectedRect);        parent->addTransition(objects.at(i), SIGNAL(clicked()), state);    }}void createAnimations(const QObjectList &objects, QStateMachine *machine){    for (int i=0; i<objects.size(); ++i)        machine->addDefaultAnimation(new QPropertyAnimation(objects.at(i), "geometry"));}#include "main.moc"         /*:qmake 不會處理.cpp檔案裡的Q_OBJECT,    *所以,如果在.cpp檔案中有它的話,    *也會產生undefined reference to vtable for "xxx::xxx".     *這時,需要先用moc xxxx.cpp產生相應的moc檔案,再包含到.cpp裡面去,    *才能解決這個問題.    **/int main(int argc, char **argv){    Q_INIT_RESOURCE(appchooser);    QApplication app(argc, argv);    Pixmap *p1 = new Pixmap(QPixmap(":/digikam.png"));    Pixmap *p2 = new Pixmap(QPixmap(":/akregator.png"));    Pixmap *p3 = new Pixmap(QPixmap(":/accessories-dictionary.png"));    Pixmap *p4 = new Pixmap(QPixmap(":/k3b.png"));    p1->setObjectName("p1");    p2->setObjectName("p2");    p3->setObjectName("p3");    p4->setObjectName("p4");    p1->setGeometry(QRectF(  0.0,   0.0, 64.0, 64.0));    p2->setGeometry(QRectF(236.0,   0.0, 64.0, 64.0));    p3->setGeometry(QRectF(236.0, 236.0, 64.0, 64.0));    p4->setGeometry(QRectF(  0.0, 236.0, 64.0, 64.0));    QGraphicsScene scene(0, 0, 300, 300);    scene.setBackgroundBrush(Qt::white);    scene.addItem(p1);    scene.addItem(p2);    scene.addItem(p3);    scene.addItem(p4);    GraphicsView window(&scene);    window.setFrameStyle(0);    window.setAlignment(Qt::AlignLeft | Qt::AlignTop);    window.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);    window.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);    QStateMachine machine;    machine.setGlobalRestorePolicy(QStateMachine::RestoreProperties);    QState *group = new QState(&machine);    group->setObjectName("group");    QRect selectedRect(86, 86, 128, 128);    QState *idleState = new QState(group);    group->setInitialState(idleState);    QObjectList objects;    objects << p1 << p2 << p3 << p4;    createStates(objects, selectedRect, group);    createAnimations(objects, &machine);    machine.setInitialState(group);    machine.start();#if defined(Q_WS_S60) || defined(Q_WS_MAEMO_5)    window.showMaximized();#else    window.resize(300, 300);    window.show();#endif    return app.exec();}

注意 #include “main.moc" 是因為這是main.cpp 所以產生的是main.moc   ， #include"main.moc”  一定要寫在後面，也可以寫在最後的位置，不能寫在開始位置，