QT之在QML中使用C++类和对象

　　QML其实是对ECMAScript的扩展，融合了Qt object系统，它是一种新的解释性语言，QML引擎虽然由Qt C++实现，但QML对象的运行环境说到底和C++对象的上下文环境是不通的，是平行的两个世界，如果想在QML中访问C++对象，那么必然要找到一种途径在两个运行环境之间建立沟通的桥梁。

　　Qt提供了两种在QML环境中使用C++对象的方式：

（1）在C++中实现一个类，注册为QML环境的一个类型，在QML环境中使用该类型创建对象

（2）在C++中构造一个对象，将这个对象设置为QML的上下文属性，在QML环境中直接使用该属性

一 类的方式实现在QML中使用C++对象

1. 定义可以导出的C++类

　　要想将一个类或对象导出到QML中，必须满足以下几个条件：

（1）从QObject或QObject的派生类继承

（2）使用Q_OBJECT宏

（3）Q_INVOKABLE宏

　　在定义一个类的成员函数时使用Q_INVOKABLE宏来修饰，就可以让该方法被元对象系统调用，这个宏必须放在返回类型前面

（4）Q_ENUMS宏

　　如果要导出的类定义了想在QML中使用的枚举类型，可以使用Q_ENUM宏将该枚举注册到元对象系统中

（5）Q_PROPERTY宏

　　Q_PROPERTY宏用来定义可以通过元对象系统访问的属性，通过它定义的属性，可以在QML中访问，修改，也可以在属性变化时发射特定的信号

  例子：

#ifndef COLORMAKER_H
#define COLORMAKER_H

#include <QObject>
#include <QColor>
class ColorMaker : public QObject
{
    Q_OBJECT
    Q_ENUMS(GenerateAlgorithm)
    Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY colorChanged)
    Q_PROPERTY(QColor timeColor READ timeColor)
public:
    explicit ColorMaker(QObject *parent = nullptr);
    ~ColorMaker();

    enum GenerateAlgorithm
    {
        RandomRGB,
        RandomRed,
        RandomGreen,
        RandomBlue,
        LinearIcrease
    };

    QColor color() const {return m_currentColor;}
    void setColor(const QColor& color);
    QColor timeColor() const;

    Q_INVOKABLE GenerateAlgorithm alorithm() const;
    Q_INVOKABLE void serAlgorithm(GenerateAlgorithm algorithm);

signals:
    void colorChanged(const QColor& color);
    void currentTime(const QString& strTime);

public slots:
    void start();
    void stop();

protected:
    void timerEvent(QTimerEvent *e);

private:
    GenerateAlgorithm m_algorithm;
    QColor m_currentColor;
    int m_nColorTimer;
};

#endif // COLORMAKER_H

#include "colormaker.h"
#include <QTime>
#include <QTimerEvent>
#include <QDebug>

ColorMaker::ColorMaker(QObject *parent)
    : QObject(parent)
    ,m_algorithm(RandomRGB)
    ,m_currentColor(Qt::black)
    ,m_nColorTimer(0)
{
    qsrand(QDateTime::currentDateTime().toTime_t());
}

ColorMaker::~ColorMaker()
{

}

void ColorMaker::setColor(const QColor &color)
{
    m_currentColor = color;
    emit colorChanged(color);
}

QColor ColorMaker::timeColor() const
{
    QTime time = QTime::currentTime();
    qDebug() << time.toString("yyyy-MM-dd hh:mm:ss");
    int r = time.hour();
    int g = time.minute() * 2;
    int b = time.second() * 4;
    qDebug() << r << ":"<< g << ":"<< b;
    return QColor(r,g,b);
}

ColorMaker::GenerateAlgorithm ColorMaker::alorithm() const
{
    return m_algorithm;
}

void ColorMaker::serAlgorithm(ColorMaker::GenerateAlgorithm algorithm)
{
    m_algorithm = algorithm;
}

void ColorMaker::start()
{
    qDebug() << "ColorMaker start";
    if (m_nColorTimer == 0)
    {
        m_nColorTimer = startTimer(1000);
    }
}

void ColorMaker::stop()
{
    if (m_nColorTimer > 0)
    {
        killTimer(m_nColorTimer);
        m_nColorTimer = 0;
    }
}

void ColorMaker::timerEvent(QTimerEvent *e)
{
    if (e->timerId() == m_nColorTimer)
    {
        switch (m_algorithm) {
        case RandomRGB:
            m_currentColor.setRgb(qrand()%255, qrand()%255,qrand()%255);
            break;
        case RandomRed:
            m_currentColor.setRed(qrand()%255);
            break;
        case RandomGreen:
            m_currentColor.setGreen(qrand()%255);
            break;
        case RandomBlue:
            m_currentColor.setBlue(qrand()%255);
            break;
        case LinearIcrease:
        {
            int r = m_currentColor.red() + 10;
            int g = m_currentColor.green() + 10;
            int b = m_currentColor.blue() + 10;
            m_currentColor.setRgb(r%255,g%255,b%255);
        }
            break;
        default:
            break;
        }
        emit colorChanged(m_currentColor);
        emit currentTime(QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss"));
    }
    else
    {
        return QObject::timerEvent(e);
    }
}

2. 注册QML类型

　　要注册一个QML类型，有多种方法：

　　qmlRegisterSingletonType()注册一个单例类型

　　qmlRegisterType()注册一个非单例类型

　　qmlRegisterTypeNotAvaliable()注册一个类型用来占位

　　qmlRegisterUncreatableType()通常用来注册一个具有附加属性的附加类型，具体参考Qt SDK

　template<typename T>
  int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName);

  template<typename T, int metaObjectRevision>
  int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName);

　　uri 指定唯一的包名

　　qmlname 是QML中可以使用的类名

qmlRegisterType<ColorMaker>("an.qt.ColorMaker", 1, 0, "ColorMaker");

3. 在QML中导入类型

　　一旦你在C++中注册好了QML类型，就可以在QML文档中引入你注册的包，然后使用注册的类型了

import an.qt.ColorMaker 1.0

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickView>
#include <QtQml>
#include "colormaker.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    //QQmlApplicationEngine engine;
    //engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    //if (engine.rootObjects().isEmpty())
    //    return -1;

    qmlRegisterType<ColorMaker>("an.qt.ColorMaker", 1, 0, "ColorMaker");
    QQuickView viewer;
    viewer.setResizeMode(QQuickView::SizeRootObjectToView);
    viewer.setSource(QUrl("qrc:///main.qml"));
    viewer.show();

    return app.exec();
}

4. 在QML中创建由C++导出的类型的实例并使用　　

　　引入包后，你可以在QML中创建 C++导入类型的对象了，与QML内建类型的使用完全一样。

Rectangle
{
     360;
    height: 360;

    ColorMaker
    {
        id:colorMaker;
        color:Qt.green;
    }
}

　　例：

import QtQuick 2.2
import QtQuick.Window 2.2
import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
import QtQuick.Dialogs 1.3
import QtQml 2.11
import an.qt.ColorMaker 1.0

Rectangle
{
     360;
    height: 360;
    Text {
        id: timeLabel;
        anchors.left: parent.left;
        anchors.leftMargin: 4;
        anchors.top : parent.top;
        anchors.topMargin: 4;
        font.pixelSize: 26;
    }

    ColorMaker
    {
        id:colorMaker;
        color:Qt.green;
    }

    Rectangle
    {
        id:colorRect;
        anchors.centerIn: parent;
         200;
        height: 200;
        color: "blue";
    }

    Button
    {
        id:start;
        text:"start";
        anchors.left: parent.left;
        anchors.leftMargin: 4;
        anchors.bottom: parent.bottom;
        anchors.bottomMargin: 4;
        onClicked:
        {
            console.log("start onClicked");
            colorMaker.start();
        }
    }

    Button
    {
        id:stop;
        text:"stop";
        anchors.left: start.right;
        anchors.leftMargin: 4;
        anchors.bottom: start.bottom;
        anchors.bottomMargin: 4;
        onClicked:
        {
            colorMaker.stop();
        }
    }

    function changeAlgorithm(button, algorithm)
    {
        switch(algorithm)
        {
        case 0:
            button.text = "RandomRGB"
            break;
        case 1:
            button.text ="RandomRed";
            break;
        case 2:
            button.text ="RandomGreen";
            break;
        case 3:
            button.text ="RandomBlue";
            break;
        case 4:
            button.text ="LinearIncrease";
            break;
        }
    }

    Button
    {
        id:colorAlgorithm;
        text:"RandomRGB";
        anchors.left:stop.right;
        anchors.leftMargin: 4;
        anchors.bottom: stop.bottom;
        onClicked:
        {
            var algorithm = (colorMaker.alorithm() + 1 ) % 5;
            changeAlgorithm(colorAlgorithm,algorithm);
            colorMaker.serAlgorithm(algorithm);
        }
    }
    Button
    {
        id:quit
        text:"quit"
        anchors.left: colorAlgorithm.right;
        anchors.leftMargin: 4;
        anchors.bottom: colorAlgorithm.bottom;
        onClicked:
        {
            Qt.quit();
        }
    }

    Component.onCompleted:
    {
        colorMaker.color = Qt.rgba(0,180,120,255);
        colorMaker.serAlgorithm(colorMaker.LinearIcrease);
        changeAlgorithm(colorAlgorithm,colorMaker.alorithm());
    }

    Connections
    {
        target: colorMaker;

        onCurrentTime:
        {
            timeLabel.text = strTime;
            console.log("onCurrentTime");
           // timeLabel.color = colorMaker.timeColor;
        }
    }

    Connections
    {
        target: colorMaker;
        onColorChanged:
        {
            colorRect.color = color;
        }
    }
}

/*Rectangle
{
     600
    height: 600

    Image {
        id: imageLabel;
         600;
        height: 540;
        anchors.top: parent.top
        anchors.left: parent.left
        fillMode: Image.PreserveAspectFit
        source: "http://images.cnblogs.com/cnblogs_com/xiaobingqianrui/1185116/o_Image%201.png"
    }

    Button
    {
        id:openBtn
         100;
        height: 40;
        text: "Open";
        anchors.top:imageLabel.bottom
        anchors.topMargin: 10;
        anchors.left: parent.left
        anchors.leftMargin: 10;
        onClicked:fileDialog.open();
    }

    Label
    {
        id:pathLabel;
        text: "Hello world"
        font.pixelSize: 22
        font.italic: true
        color: "steelblue"

        anchors.top:imageLabel.bottom
        anchors.topMargin: 10;
        anchors.left: openBtn.right
        anchors.leftMargin: 10
    }

    FileDialog
    {
        id:fileDialog
        title: "please choose a file"
        nameFilters: ["Image Files (*.jpg *.png *.gif)"]
        onAccepted:
        {
            imageLabel.source=fileDialog.fileUrl;
            console.log(fileDialog.fileUrl);
            var imageFile = new String(fileDialog.fileUrl);
            pathLabel.text=imageFile.slice(8);
        }
    }
}*/

二 对象的方式实现在QML中使用C++对象

1. 注册属性

viewer.rootContext()->setContextProperty("colorMaker", new ColorMaker);

2. 在QML中使用关联到的C++对象的属性

　　一旦调用setContextProperty()导出了属性，就可以在QML中使用了，不需要import语句

import QtQuick 2.2
import QtQuick.Window 2.2
import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
import QtQuick.Dialogs 1.3
import QtQml 2.11
//import an.qt.ColorMaker 1.0

Rectangle
{
     360;
    height: 360;
    Text {
        id: timeLabel;
        anchors.left: parent.left;
        anchors.leftMargin: 4;
        anchors.top : parent.top;
        anchors.topMargin: 4;
        font.pixelSize: 26;
    }

   /* ColorMaker
    {
        id:colorMaker;
        color:Qt.green;
    }*/

    Rectangle
    {
        id:colorRect;
        anchors.centerIn: parent;
         200;
        height: 200;
        color: "blue";
    }

    Button
    {
        id:start;
        text:"start";
        anchors.left: parent.left;
        anchors.leftMargin: 4;
        anchors.bottom: parent.bottom;
        anchors.bottomMargin: 4;
        onClicked:
        {
            console.log("start onClicked");
            colorMaker.start();
        }
    }

    Button
    {
        id:stop;
        text:"stop";
        anchors.left: start.right;
        anchors.leftMargin: 4;
        anchors.bottom: start.bottom;
        anchors.bottomMargin: 4;
        onClicked:
        {
            colorMaker.stop();
        }
    }

    function changeAlgorithm(button, algorithm)
    {
        switch(algorithm)
        {
        case 0:
            button.text = "RandomRGB"
            break;
        case 1:
            button.text ="RandomRed";
            break;
        case 2:
            button.text ="RandomGreen";
            break;
        case 3:
            button.text ="RandomBlue";
            break;
        case 4:
            button.text ="LinearIncrease";
            break;
        }
    }

    Button
    {
        id:colorAlgorithm;
        text:"RandomRGB";
        anchors.left:stop.right;
        anchors.leftMargin: 4;
        anchors.bottom: stop.bottom;
        onClicked:
        {
            var algorithm = (colorMaker.alorithm() + 1 ) % 5;
            changeAlgorithm(colorAlgorithm,algorithm);
            colorMaker.serAlgorithm(algorithm);
        }
    }
    Button
    {
        id:quit
        text:"quit"
        anchors.left: colorAlgorithm.right;
        anchors.leftMargin: 4;
        anchors.bottom: colorAlgorithm.bottom;
        onClicked:
        {
            Qt.quit();
        }
    }

    Component.onCompleted:
    {
        colorMaker.color = Qt.rgba(0,180,120,255);
        //colorMaker.serAlgorithm(colorMaker.LinearIcrease);
        colorMaker.serAlgorithm(2);
        changeAlgorithm(colorAlgorithm,colorMaker.alorithm());
    }

    Connections
    {
        target: colorMaker;

        onCurrentTime:
        {
            timeLabel.text = strTime;
            console.log("onCurrentTime");
           // timeLabel.color = colorMaker.timeColor;
        }
    }

    Connections
    {
        target: colorMaker;
        onColorChanged:
        {
            colorRect.color = color;
        }
    }
}