QML与C++的信号连接（C++发送信号）

1、不采用在.qml文件中实例化C++类的方式，因此在main.cpp中注册单例

#include"myobject.h"

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QScreen>
#include <QObject>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    //注册单例
    qmlRegisterSingletonInstance<MyObject>("MyObj", 1, 0, "MyObject", MyObject::getInstance());

    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreationFailed,
        &app,
        []() { QCoreApplication::exit(-1); },
        Qt::QueuedConnection);
    engine.loadFromModule("updatePublisher", "Main");

    return app.exec();
}

此时在cpp类中发送信号

void MyObject::func()
{
    emit cppSig(101, "hello");
}

在.qml中控制cpp类发送信号，并在.qml中使用Connections建立连接

import QtQuick
import QtQuick.Controls
import MyObj 1.0

Window {
    id: window
    objectName: "window"
    width: 480
    height: 480
    visible: true
    title: qsTr("Hello World")

    //槽函数
    function qmlSlot(i, s) {
        console.log("qml", i, s)
    }

    Button {
        id: btn
        objectName: "button"
        signal qmlSig(int i, string s)

        //按下按钮后，调用cpp类的func函数，在函数中发送信号
        onClicked: {
            MyObject.func()
        }
    }

    //建立信号槽连接
    Connections {
        target: MyObject
        function onCppSig(i, s) {
            qmlSlot(i, s)
        }
    }
}

2、在main.cpp中建立连接

#include"myobject.h"

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QScreen>
#include <QObject>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    qmlRegisterSingletonInstance<MyObject>("MyObj", 1, 0, "MyObject", MyObject::getInstance());

    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreationFailed,
        &app,
        []() { QCoreApplication::exit(-1); },
        Qt::QueuedConnection);
    engine.loadFromModule("updatePublisher", "Main");

    auto list = engine.rootObjects();
    auto window = list.first();

    //参数类型一定要用QVariant
    QObject::connect(MyObject::getInstance(), SIGNAL(cppSig(QVariant, QVariant)), window, SLOT(qmlSlot(QVariant, QVariant)));

    return app.exec();
}