QML学习十四：C++访问QML函数

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QML学习十四：C++访问QML函数

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记录C++端如何访问QML端的函数，QML端访问C++端函数只需要声明就可以访问，那么C++端要如何访问QML端函数呢？

举个例子，在main.qml里有个函数qmlFunc()，我们希望C++可以访问这个函数返回success的返回值。

 一、获取对象

通过QMetaObject::invokemethod()来调用QML端的函数，具体函数详细请查询QT助手。

 二、完整代码

1、main.qml 

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12import MyObj 1.0Window {id: windowvisible: truewidth: SCREEN_WIDTHheight: 480objectName: windowtitle: qsTr("Hello World")signal qmlSig(int i, string s)function qmlFunc(i, s) {return "success"}Button {onClicked: {//myobj.cppSig(99, "lisi")MyObject.func();}}//    Connections {
//        target: MyObject
//        function onCppSig(i, s) {
//            qmlSlot(i, s)
//        }
//    }
}

2、main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "myobject.h"int main(int argc, char *argv[])
{QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);QGuiApplication app(argc, argv);app.setOrganizationName("myApp");QQmlApplicationEngine engine;QQmlContext *context = engine.rootContext();context->setContextProperty("SCREEN_WIDTH", 800);//    MyObject obj;
//    context->setContextProperty("MyObject", &obj);//    context->setContextProperty("MyObject", MyObject::getInstance());qmlRegisterType<MyObject>("MyObj", 1, 0, "MyObject");qmlRegisterSingletonInstance("MyObj", 1, 0, "MyObject", MyObject::getInstance());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);// engine 加载完成后 load以后auto list = engine.rootObjects();auto window = list.first();QObject::connect(window, SIGNAL(qmlSig(int, QString)),MyObject::getInstance(), SLOT(cppSlot(int, QString)));QObject::connect(MyObject::getInstance(), SIGNAL(cppSig(int, QString)),window, SLOT(qmlSlot(int, QString)));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();
}

通过代码可以看出，结果打印了返回值，返回类开QVariant。

3、结果

三、总结

在实际项目中，目前为上，C++端调用QML函数很少用到，用到最多的还是单便模式，即QML端访问C++端。

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