• 一、QML访问C++方法
  1. Qt元对象系统中注册C++类，在QML中实例化、访问。
  2. C++中实例化并设置为QML上下文属性，在QML中直接使用。

比较：方法1可以使C++类在QML中作为一个数据类型，例如函数参数类型或属性类型，也可以使用其枚举类型、单例等，功能更强大。

  • 二、QML访问C++条件
  1. 派生自QObject类或QObject类的子类
  2. 使用Q_OBJECT宏
  • 三、QML访问C++举例

使用方法1

信号与槽

#ifndef GEMINI_H  #define GEMINI_H  #include   #include   class Gemini : public QObject  {      Q_OBJECT  signals:    //1、先定义“信号”    void begin();   public slots:  //1、先定义“槽”    void doSomething() {          qDebug() << "Gemini::doSomething() called";      }  };  #endif 
#include   #include   #include   #include   int main(int argc, char *argv[])  {      QGuiApplication app(argc, argv);      qmlRegisterType("Union.Lotto.Gemini", 1, 0, "Gemini");  //一.注册c++类    QQmlApplicationEngine engine;      engine.load(QUrl(QStringLiteral("qrc:///main.qml")));      return app.exec();  }
import QtQuick 2.2  import QtQuick.Window 2.1  import Union.Lotto.Gemini 1.0  //二.导入Window {      visible: true      width: 360; height: 360      title: "Union Lotto Game"      color: "white"      MouseArea {          anchors.fill: parent          onClicked: {              gemini.begin()  //2.调用类信号        }      }      Gemini {          id: gemini          onBegin: doSomething()  //2.调用类槽    }  }

2、枚举类型

#ifndef GEMINI_H  #define GEMINI_H  #include   #include   class Gemini : public QObject  {      Q_OBJECT      Q_ENUMS(BALL_COLOR)  //1、先定义。枚举类型在QML中使用，就用到了Q_ENUMS()宏public:      Gemini() : m_ballColor(BALL_COLOR_YELLOW) {          qDebug() << "Gemini::Gemini() called";      }      enum BALL_COLOR {          BALL_COLOR_YELLOW,          BALL_COLOR_RED,          BALL_COLOR_BLUE,          BALL_COLOR_ALL      };  signals:      void begin();  public slots:      void doSomething(BALL_COLOR ballColor) {          qDebug() << "Gemini::doSomething() called with" << ballColor;          if(ballColor != m_ballColor) {              m_ballColor = ballColor;              qDebug() << "ball color changed";          }      }  private:      BALL_COLOR m_ballColor;  };  #endif 
import QtQuick 2.2  import QtQuick.Window 2.1  import Union.Lotto.Gemini 1.0  Window {      visible: true      width: 360; height: 360      title: "Union Lotto Game"      color: "white"      MouseArea {          anchors.fill: parent          onClicked: {              gemini.begin()          }      }      Gemini {          id: gemini          onBegin: doSomething(Gemini.BALL_COLOR_RED)  //2.调用，在QML中使用枚举类型的方式是.    }  }

3、成员函数

#ifndef GEMINI_H  #define GEMINI_H  #include   #include   class Gemini : public QObject  {      Q_OBJECT      Q_ENUMS(BALL_COLOR)  public:      Gemini() : m_ballColor(BALL_COLOR_YELLOW) {          qDebug() << "Gemini::Gemini() called";      }      enum BALL_COLOR {          BALL_COLOR_YELLOW,          BALL_COLOR_RED,          BALL_COLOR_BLUE,          BALL_COLOR_ALL      };      Q_INVOKABLE void stop() {  //1、定义。访问的前提是public或protected成员函数，且使用Q_INVOKABLE宏        qDebug() << "Gemini::stop() called";      }  signals:      void begin();  public slots:      void doSomething(BALL_COLOR ballColor) {          qDebug() << "Gemini::doSomething() called with" << ballColor;          if(ballColor != m_ballColor) {              m_ballColor = ballColor;              qDebug() << "ball color changed";          }      }  private:      BALL_COLOR m_ballColor;  };  #endif 
import QtQuick 2.2  import QtQuick.Window 2.1  import Union.Lotto.Gemini 1.0  Window {      visible: true      width: 360; height: 360      title: "Union Lotto Game"      color: "white"      MouseArea {          anchors.fill: parent          onClicked: {              gemini.begin()              gemini.stop()  //2、调用，在QML中访问C++的成员函数的形式是.        }      }      Gemini {          id: gemini          onBegin: doSomething(Gemini.BALL_COLOR_RED)      }  }

4、C++类的属性

#ifndef GEMINI_H  #define GEMINI_H  #include   #include   class Gemini : public QObject  {      Q_OBJECT      Q_ENUMS(BALL_COLOR)      Q_PROPERTY(unsigned int ballNumber READ ballNumber WRITE setBallNumber NOTIFY ballNumberChanged)  //1、定义，Q_PROPERTY()宏，用来在QObject派生类中声明属性。public:      Gemini() : m_ballColor(BALL_COLOR_YELLOW), m_ballNumber(0) {          qDebug() << "Gemini::Gemini() called";      }      enum BALL_COLOR {          BALL_COLOR_YELLOW,          BALL_COLOR_RED,          BALL_COLOR_BLUE,          BALL_COLOR_ALL      };      unsigned int ballNumber() const {          return m_ballNumber;      }      void setBallNumber(const unsigned int &ballNumber) {          if(ballNumber != m_ballNumber) {              m_ballNumber = ballNumber;              emit ballNumberChanged();          }      }      Q_INVOKABLE void stop() {          qDebug() << "Gemini::stop() called";      }  signals:      void begin();      void ballNumberChanged();  public slots:      void doSomething(BALL_COLOR ballColor) {          qDebug() << "Gemini::doSomething() called with" << ballColor;          if(ballColor != m_ballColor) {              m_ballColor = ballColor;              qDebug() << "ball color changed";          }      }  private:      BALL_COLOR m_ballColor;      unsigned int m_ballNumber;  };  #endif
import QtQuick 2.2  import QtQuick.Window 2.1  import Union.Lotto.Gemini 1.0  Window {      visible: true      width: 360; height: 360      title: "Union Lotto Game"      color: "white"      MouseArea {          anchors.fill: parent          onClicked: {              gemini.begin()              gemini.stop()              gemini.ballNumber = 10  //2、调用，Gemini类中的ballNumber属性可以在QML中访问、修改，访问时调用了ballNumber()函数，
                                    //        修改时调用了setBallNumber()函数，同时还发送了一个信号来自动更新这个属性值。        }      }      Gemini {          id: gemini          onBegin: doSomething(Gemini.BALL_COLOR_RED)          onBallNumberChanged: console.log("new ball number is", ballNumber) // 10          Component.onCompleted: console.log("default ball number is", ballNumber) // 0      }  }

备注：1、参考网址：https://zhuanlan.zhihu.com/p/633999343

2、本文只为个人学习笔记，其他第三方可以任意使用。