c++ - 使用双击事件创建 QLabel 时出现链接器错误

Question

我正在创建一个 QLabel 子类，它向其中添加了 DoubleClickEvent。我创建了以下内容，但出现了一些奇怪的链接器错误，也许有人可以指出我做错了什么？

//Header
#ifndef IMAGE_LABEL_H
#define IMAGE_LABEL_H

#include <QLabel>
#include <QMouseEvent>

class image_label : public QLabel
{
    Q_OBJECT
public:
image_label(QWidget* parent = 0);
~image_label();

signals:
    void doubleClicked();

protected:
    void mouseDoubleClickEvent(QMouseEvent * e);

};


#endif


//CPP 

#include "image_label.h"
#include <QMouseEvent>

image_label::image_label(QWidget* parent) : QLabel(parent)
{
}

image_label::~image_label()
{
}

void image_label::mouseDoubleClickEvent(QMouseEvent* e)
{
    if (e->button() == Qt::LeftButton)
    {
        emit doubleClicked();
        QLabel::mouseDoubleClickEvent(e);
    }
}

编译时出现以下链接器错误:

 image_label.obj : error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __thiscall image_label::metaObject(void)const " (?metaObject@image_label@@UBEPBUQMetaObject@@XZ)

  image_label.obj : error LNK2001: unresolved external symbol "public: virtual void * __thiscall image_label::qt_metacast(char const *)" (?qt_metacast@image_label@@UAEPAXPBD@Z)

  image_label.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall image_label::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@image_label@@UAEHW4Call@QMetaObject@@HPAPAX@Z)

  image_label.obj : error LNK2019: unresolved external symbol "protected: void __thiscall image_label::doubleClicked(void)" (?doubleClicked@image_label@@IAEXXZ) referenced in function "protected: virtual void __thiscall image_label::mouseDoubleClickEvent(class QMouseEvent *)" (?mouseDoubleClickEvent@image_label@@MAEXPAVQMouseEvent@@@Z)

谁能帮我解释为什么会出现这些错误？

Answer 1

您必须在文件 image_label.h 上运行 MOC 预处理器。这会生成一个文件 moc_image_label.cpp，您必须将其包含在构建中。错误消息表明您还没有这样做。 (错误信息中提到的image_label::metaObject等符号在moc_image_label.cpp中定义。)