QML与C++几种交互方式

QML调用CPP函数

要求：

• 使用 Q_OBJECT 宏需要继承 QObject 类。Q_OBJECT能够启用信号和槽机制、使用动态属性系统。（使用 Q_OBJECT 宏的类需要通过Qt的元对象编译器（moc）进行处理。）
• 使用 Q_INVOKABLE 修饰要暴露给 QML 的函数。

1.在main.cpp中进行注册

 // 注册c++类到qml  参数分别为导入的 模块名称  主版本号  次版本号  模块名称
 qmlRegisterType<CppObject>("CppObject",1,0,"CppObject");

2.在qml中导入

import CppObject 1.0
 CppObject{
       id:cppobj
   }

3.通过id+方法名的方式调用

   // 加上这个宏，当前函数就可以被qml访问调用
    Q_INVOKABLE void func();

//test.h
#ifndef TEST_H
#define TEST_H

#include <QObject>
#include "QDebug"
class CppObject : public QObject
{
    Q_OBJECT
public:
    explicit CppObject(QObject *parent = nullptr);
    //通过宏定义在qml使用cpp类中的函数
    Q_INVOKABLE void print_(QString str)
    {
        qDebug()  << str;
    }

};
#endif // TEST_H

//main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include <QLocale>
#include <QTranslator>
#include "test.h"
int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
    QGuiApplication app(argc, argv);

    QTranslator translator;
    const QStringList uiLanguages = QLocale::system().uiLanguages();
    for (const QString &locale : uiLanguages) {
        const QString baseName = "untitled_" + QLocale(locale).name();
        if (translator.load(":/i18n/" + baseName)) {
            app.installTranslator(&translator);
            break;
        }
    }

	//主要是这里其他的都是默认的
    // 注册c++类到qml  参数分别为导入的 模块名称  主版本号  次版本号  模块名称
    qmlRegisterType<CppObject>("CppObject",1,0,"CppObject");



    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreated,
        &app,
        [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        },
        Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

//main.qml
import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15
import CppObject 1.0

Window {
    id: win
    width: 800
    height: 600
    visible: true
    title: qsTr("Hello World")

    CppObject{
            id:cppobj
        }

    Button{
            width: 50
            height: 50
            background: Rectangle{
                color:"red"
            }
            onClicked: {
                //obj.printMsg()
                cppobj.print_("test")
            }
        }

}

定义全局变量，注册到上下文

样例：

#include <QQmlContext>
QQmlApplicationEngine engine;
//这两句是重点，设置全局变量
QQmlContext *context = engine.rootContext();
context->setContextProperty("SCREEN_WIDTH", 800);

也可以用此方法将类对象暴露给QMLsetContextProperty两个参数表示的意义为:

• 第一个参数表示 qml 可以识别的对象名
• 第二个参数表示 C++ 对象

#include <QtQml/QQmlContext>
#include "vacUdpClient.h"
 
/*** main.cpp ***/
vacUdpClient udpclient;
QQmlContext* context = engine.rootContext();
context->setContextProperty("udpclient", &udpclient);

使用时候当变量用就行，SCREEN_WIDTH为变量名

//main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QLocale>
#include <QTranslator>
//全局变量必须得头文件
#include <QQmlContext>

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
    QGuiApplication app(argc, argv);

    QTranslator translator;
    const QStringList uiLanguages = QLocale::system().uiLanguages();
    for (const QString &locale : uiLanguages) {
        const QString baseName = "untitled_" + QLocale(locale).name();
        if (translator.load(":/i18n/" + baseName)) {
            app.installTranslator(&translator);
            break;
        }
    }

    QQmlApplicationEngine engine;
    //这两句是重点，设置全局变量
    QQmlContext *context = engine.rootContext();
    context->setContextProperty("SCREEN_WIDTH", 800);



    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreated,
        &app,
        [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        },
        Qt::QueuedConnection);
    engine.load(url);
    return app.exec();
}

//main.qml
import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15
Window {
    id: window
    visible: true
    //使用全局变量
    width: SCREEN_WIDTH
    height: 500
    title: qsTr("Hello World")

    Button{
        width: 100
        height: 100
        background: {
            color:"black"
        }
    }
}

CPP访问QML函数

//main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QLocale>
#include <QTranslator>


int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
    QGuiApplication app(argc, argv);

    QTranslator translator;
    const QStringList uiLanguages = QLocale::system().uiLanguages();
    for (const QString &locale : uiLanguages) {
        const QString baseName = "untitled_" + QLocale(locale).name();
        if (translator.load(":/i18n/" + baseName)) {
            app.installTranslator(&translator);
            break;
        }
    }

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreated,
        &app,
        [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        },
        Qt::QueuedConnection);
    engine.load(url);


    //重点
    auto list = engine.rootObjects();
    auto window = list.first();
    QVariant res;
    QVariant arg_1 = 123;
    QVariant arg_2 = "zhangsan";
    QMetaObject::invokeMethod(window, "qmlFunc",Q_RETURN_ARG(QVariant, res),Q_ARG(QVariant, arg_1),Q_ARG(QVariant, arg_2));

    qDebug() << "res = " << res;


    return app.exec();
}

//main.qml
import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15


Window {
    id: window
    visible: true
    width: SCREEN_WIDTH
    height: 500
    title: qsTr("Hello World")


    //供C++端调用的函数
    function qmlFunc(i, s) {
            return "success"
        }

   
}

单实例注册类

main.cpp文件里加这个

 // qml单实例注册
qmlRegisterSingletonInstance("PersonMudle", 1, 0, "MyPerson", &person);

以下这样使用

import PersonMudle 1.0
	Button {
            objectName: "qml_button"
            text: "QML button"
            font.pixelSize: 25
 
            onClicked: {
                MyPerson.showInfo()
            }
        }

信号与槽

	//加在main.cpp中
   // engine 加载完成后 load以后
   auto list = engine.rootObjects();
   //auto objName = list.first()->objectName(); // 获取第一个objname
   //auto mybuttonObj = list.first()->findChild<QObject *>("mybutton");
   auto window = list.first();
	
	//槽函数链接
	// 第一个参数为组件
	// 第二个为信号名
	// 第三个为类的实例化
	// 第三个为槽函数
   QObject::connect(window,SIGNAL(qmlSig(int,QString)),
                    CppObject::getInstance(),SLOT(cppSlot(int,QString)));

例子：

	//类
	Person person("张三", 18);
	//上下文: 将类对象注册到QML的上下文背景中
    auto ctext = engine.rootContext();
    ctext->setContextProperty("OtPerson", &person);
 
    //cpp获取qml中的指定对象
    auto rootObj = engine.rootObjects();
    // rootObj.first()获取所有对象列表
    auto button = rootObj.first()->findChild<QObject*>("qml_button");
    // 使用QT4的方式绑定信号和槽： qml的信号，cpp的槽
    QObject::connect(button, SIGNAL(clicked()), &person, SLOT(clickButton()));
    QObject::connect(button, SIGNAL(coutNum(int)), &person, SLOT(clickCal(int)));
    /*
    // 使用QT5的方式绑定信号和槽不可行，此处button is nullptr
    auto button = rootObj.first()->findChild<QPushButton*>("qml_button");
    if (!button) {
        qDebug() << "button is nullptr";
    }
    QObject::connect(button, &QAbstractButton::clicked, &person, &Person::clieckButton);
    */

//main.qml
import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15 as QtCtrl
import QtQuick.Layouts 1.0
 
 
Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("qml和cpp交互总结")
 
    Item {
        id: item
        anchors.fill: parent
 
        QtCtrl.Button {
            objectName: "qml_button"
            text: "QML button"
            font.pixelSize: 25
            property int cal: 1
            // qml中自定义信号
            signal coutNum(int num)
 
            onClicked: {
                OtPerson.showInfo()
                if (0 == cal++ % 10) {
                    coutNum(cal)
                }
            }
        }
    }
 
}

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