无法使qmlRegisterType工作 [英] Unable to make qmlRegisterType work

问题描述

我在互联网上找到了qmlRegisterType的一些示例，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:

I've found some examples of qmlRegisterType on the internet but just can't make it work. I create a new Qt Quick 2 project and add the following contents:

这是我的.pro文件:

This is my .pro file:

#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):

This is my code file (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):

This is my QML file (main.qml):

import QtQuick 2.0
import testlib 1.0

Rectangle {

  TestClass {
    id:testobj
  }

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

但是我遇到了多个链接错误:

• 未定义对"vClass for TestClass"的引用
• 对"TestClass :: staticMetaObject"的未定义引用
• 对`TestClass :: metaObject()const'的未定义引用
• 对`TestClass :: qt_metacast(char const *)'的未定义引用
• 对`TestClass :: qt_metacall(QMetaObject :: Call，int，void **)'的未定义引用

我使用的是MinGW 4.8稳定版随附的Qt 5.2.1.这些错误意味着链接器找不到包含方法实现(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上可以吗?

I'm using Qt 5.2.1 shipped with MinGW 4.8 stable. These errors mean the linker can not find library files which contain method implementations (stated above). What happened? May be fail to compile on Qt 5 but ok on Qt 4?

推荐答案

有关使用Qt进行编译的说明:

Notes about compilation with Qt:

(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

有关创建自定义QML组件(以下称为"CustomCom")的注意事项:

Notes about creating a custom QML component (herefrom called 'CustomCom'):

(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. 

示例标头代码:

[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();
}

QML示例:

[main.qml]
import QtQuick 2.0
import CustomLib 1.0

Rectangle {
  width:640; height:360;

  CustomCom {
    id:customcom;
  }

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

问题的解决方案(面向对vtable的未定义引用"):

Solution to the question (facing 'Undefined reference to vtable'):

• 合并"TestClass.hpp"和将"TestClass.cpp"转换为"TestClass.hpp"文件
• 将"TestClass.hpp"的内容移至"main.hpp"

该问题是由使用主标头文件引起的.仅在需要时放置#include即可解决问题.

The problem was caused by using master header file. Putting the #include(s) only when needed solves the problem.

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