我在 Internet 上找到了一些 qmlRegisterType 的示例，但无法使其正常工作。我创建一个新的 Qt Quick 2 项目并添加以下内容:

这是我的 .pro 文件:

#Add more folders to ship with the application, here
folder_01.source = qml/testlib
folder_01.target = qml
DEPLOYMENTFOLDERS = folder_01

#Libraries
QT += core gui widgets

#Additional import path used to resolve QML modules in Creator's code model
QML_IMPORT_PATH =

#Header files
HEADERS += main.hpp

#The .cpp file which was generated for your project. Feel free to hack it.
SOURCES += main.cpp

#Installation path
#target.path =

#Please do not modify the following two lines. Required for deployment.
include(qtquick2applicationviewer/qtquick2applicationviewer.pri)
qtcAddDeployment()

这是我的代码文件(main.cpp):

#include <QtQml>
#include <QtWidgets/QApplication>
#include "qtquick2applicationviewer.h"

//test class
class TestClass:public QObject {
  Q_OBJECT

  public:
    TestClass(QObject* parent=0):QObject(parent){}

  public slots:
    void test() {
      qDebug("test!");
    }
};

//entry point
int main(int argc, char *argv[]) {

  //create application
  QApplication app(argc, argv);

  //register custom qml component
  qmlRegisterType<TestClass>("testlib",1,0,"TestClass");

  //create and show qml viewer
  QtQuick2ApplicationViewer viewer;
  viewer.setMainQmlFile(QStringLiteral("qml/testlib/main.qml"));
  viewer.showExpanded();

  //back to OS
  return app.exec();
}

这是我的 QML 文件 (main.qml):

import QtQuick 2.0
import testlib 1.0

Rectangle {

  TestClass {
    id:testobj
  }

  Component.onCompleted: {
    testobj.test();
  }
}

但我遇到多个链接错误:

• 对“TestClass 的 vtable”的 undefined reference
• 对“TestClass::staticMetaObject”的 undefined reference
• 对“TestClass::metaObject() const”的 undefined reference
• 对“TestClass::qt_metacast(char const*)”的 undefined reference
• 对 `TestClass::qt_metacall(QMetaObject::Call, int, void**)' 的 undefined reference

我正在使用 MinGW 4.8 稳定版附带的 Qt 5.2.1。这些错误意味着链接器无法找到包含方法实现(如上所述)的库文件。 发生了什么事？可能无法在 Qt 5 上编译但在 Qt 4 上正常？

最佳答案

Qt编译注意事项:

(1) Use 'QT +=' in .pro file for Qt headers & Qt libraries

(2) Use 'HEADERS +=' and 'SOURCES +=' in .pro file for 
project level headers and source codes

关于创建自定义 QML 组件(以下称为“CustomCom”)的注意事项:

(1) Inherit publically 'CustomCom' from QQuickItem: 

class CustomCom:public QQuickItem {}

(2) Put the Q_OBJECT macro right after first line of 
class 'CustomCom' declaration.

(3) Inherit the constructor:

public: CustomCom(QQuickItem* parent=0):QQuickItem(parent){}

(4) Put the methods to be called by JS after "public slots:"

(5) Call 'qmlRegisterType' after creation of 'QApplication' and
before creating any QML view or viewer.

(6) IMPORTANT: If you fail to compile with error 
'undefined reference to vtable...", just put the code of 'CustomCom.cpp'
nested inside the 'CustomCom.hpp' file, and put the whole code 
of the class 'CustomCom.hpp' in the main header file because of
something wrong in header referencing. 

示例 header 代码:

[main.hpp]
class CustomCom:public QQuickItem {
  Q_OBJECT

  public:
    CustomCom(QQuickItem* parent=0):QQuickItem(parent){}

  public slots:
    void test() {
      qDebug("Test!");
    }
};

示例源代码:

[main.cpp]
int main(int argc,char** args) {
  QApplication* app = new QApplication(argc,args);

  //call before any qml may use the custom component
  qmlRegisterType<CustomCom>("CustomLib",1,0,"CustomCom");

  //class 'QtQuick2ApplicationViewer' is generated by Qt Creator
  //when creating new Quick 2 project. The path to 'main.qml'
  //may be different
  QtQuick2ApplicationViewer* viewer = new QtQuick2ApplicationViewer();
  viewer->setMainQmlFile("qml/project/main.qml");
  viewer->showExpanded();
}

示例 QML:

[main.qml]
import QtQuick 2.0
import CustomLib 1.0

Rectangle {
  width:640; height:360;

  CustomCom {
    id:customcom;
  }

  Component.onCompleted: {
    customcom.test();
  }
}

题解(面对'Undefined reference to vtable'):

• 将“TestClass.hpp”和“TestClass.cpp”合并为“TestClass.hpp”文件
• 将'TestClass.hpp'的内容移动到'main.hpp'

问题是使用master头文件引起的。仅在需要时放置#include(s) 可以解决问题。

关于c++ - 无法使 qmlRegisterType 工作，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22240421/