Qt quick 与 C++通信（一） Signal 和slot

.message.h

#ifndef MESSAGE_H
#define MESSAGE_H

#include <QObject>
#include <QQuickItem>

class Message : public QObject
{
        Q_OBJECT
    public:
        explicit Message(QObject *parent = 0);
    public slots:
        void doMessageChange();
    signals:
        void messageChanged(QString value);

    private:
        int m_counter;
        QString m_message;
        explicit Message(const Message & rhs) = delete;
        Message& operator = (const Message& rhs) = delete;
};

#endif // MESSAGE_H

message.cpp

#include "message.h"
#include <iostream>


Message::Message(QObject *parent):
    QObject (parent),
    m_counter(0),
    m_message("Hello New World! %1")
{

}

void Message::doMessageChange()
{
    ++m_counter;
    emit messageChanged(m_message.arg(m_counter));
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "message.h"
int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    Message my_msg;
    auto root_context = engine.rootContext();
    root_context->setContextProperty("messageClasee",&my_msg);


    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.Window 2.12
import QtQuick.Controls 2.5
Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Connections{
        target:messageClasee
        onMessageChanged: textId.text = value;
    }

    Column{
        Text {
            id :textId
            text: qsTr("Hellow New World")
            font.pointSize: 20

        }
        Button{
            text:"Change Text"
            onClicked: messageClasee.doMessageChange()
        }
    }
}