第九章：QML中多线程的使用

Connections介绍: https://doc.qt.io/qt-5/qml-qtqml-connections.html

示例：倒计时

 worker.h

#ifndef DISPATCHER_H
#define DISPATCHER_H

#include <QThread>
#include <QDebug>

class Worker : public QThread
{
    Q_OBJECT
    Q_PROPERTY(int data READ getData WRITE setData NOTIFY dataChanged )

public:
    explicit Worker() = default;
    ~Worker() = default;
    void run() {
        qDebug() << "Inside the worker thread!";
        for ( int i = 10; i >= 0; --i ) {
            setData(i);
            sleep( 1 );
        }
    }

    Q_INVOKABLE int getData() const { return data_; }

// TODO: add signals for each type of received message by the worker thread?
signals:
    void dataChanged( const int data );

public slots:
    void setData( const int data ) {
        if ( data != data_ ) {
            data_ = data;
            emit dataChanged( data_ );
        }
    }

private:
    int data_ = 0 ;
};

#endif // DISPATCHER_H

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QThread>
#include <QQmlEngine>
#include <QQmlContext>

#include "worker.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    Worker worker;
    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("theworker", &worker);
    engine.load(QUrl(QLatin1String("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

main.qml

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3

ApplicationWindow {
    id: root
    visible: true
    width: 640
    height: 480
    title: qsTr("线程")

    Rectangle {
        color: "orange"
        anchors.fill: parent
        objectName: "test"
        Text {
            id: thetext
            text: "倒计时"
            verticalAlignment: Text.AlignVCenter
            horizontalAlignment: Text.AlignHCenter
            textFormat: Text.AutoText
            fontSizeMode: Text.FixedSize
            font.pointSize: 40
            anchors.horizontalCenter: parent.horizontalCenter
            anchors.fill: parent

            Button {
                id: startbutton
                x: 503
                y: 406
                text: qsTr("开始")
                onClicked: {
                    theworker.start()  // 开启线程
                }
            }
        }
    }

    Connections {  //连接的目标不在QML中
        target: theworker  //指向发出信号的对象
        onStarted: {
            print('线程开启')
        }

        onDataChanged: {
            print('计时改变: ' + theworker.getData() );
            thetext.text = theworker.getData();
        }
    }

    Component.onDestruction: theworker.terminate();
}