将 QVariant 从 QML 传递到 C++

Question

我正在尝试将列表从 QML 发送到 c++。我尝试使用字符串和整数成功，但是当我尝试使用 QVariant 时出现错误：

QObject::connect: ../test_2206/main.cpp:31 中没有这样的插槽 MyClass::cppSlot(QVariant)

我的 main.qml

import QtQuick 2.4
import QtQuick.Layouts 1.1
import Material.ListItems 0.1 as ListItem
import Material.Extras 0.1
import QtQuick.Controls 1.3 as QuickControls
import QtQuick.Controls 1.4
import Material 0.2


Window {
    visible: true
    property var listCloud: ["nuage1", "nuage2", "nuage3", "nuage4"]
        id: item
        width: 100; height: 100

        signal qmlSignal(variant msg)

       /* MouseArea {
            anchors.fill: parent
            onClicked: item.qmlSignal("Hello from QML")
        }*/
    Rectangle{
        id:sousRect
        color:"red"
        width:100; height:100
            Button{
                id:buttonTest
                onClicked: {
                     item.qmlSignal(listCloud)
                }
            }
    }

}

我的 main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlProperty>
#include <QQmlComponent>
#include <QDebug>
#include "myclass.h"

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

    QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/main.qml")));
    QObject *object = component.create();

        MyClass myClass;
        QObject::connect(object, SIGNAL(qmlSignal(QVariant)),
                         &myClass, SLOT(cppSlot(QVariant)));


    return app.exec();
}

我的 myclass.h

#ifndef MYCLASS_H
#define MYCLASS_H
#include <QDebug>
#include <QString>
#include <QList>



class MyClass : public QObject
{
    Q_OBJECT
public:
    MyClass(QObject *parent = 0);
signals:
public slots:
    void cppSlot(QVariant &msg);
};

#endif // MYCLASS_H

我的 myclass.cpp

#include "myclass.h"

MyClass::MyClass(QObject *parent):
    QObject(parent)
{

}
void MyClass::cppSlot(QVariant &msg){
    qDebug() << "c++: bien reçu chef " << msg;
}

我不明白为什么我不能在这个信号中加入 QVariant 参数。 欢迎任何帮助:)

Answer 1

更改您的插槽以通过值而不是通过引用接收他的参数。像这样：

    void cppSlot(QVariant msg);

我认为这与 QML 拒绝通过引用传递 Window 的属性有关。无论如何，Qt 经常发送信号 by-value，即使您的信号/槽签名[s] 声明了参数 by-reference。有关该主题的更多信息，请参阅 this 和 that

Answer 2

不要在 QML 和 C++ 之间使用引用，它们不会起作用。

void cppSlot(QVariant & msg);

您还可以在 C++ 中创建 Q_INVOKABLE 函数并直接从 QML 调用它。这是它的样子：

ma​​in.cpp：

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlProperty>
#include <QQmlComponent>
#include <QDebug>
#include "myclass.h"

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

    auto myobject = new MyClass(&app);
    engine.rootContext()->setContextProperty(QStringLiteral("myobject"), myobject);

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
    {
        return -1;
    }

    return app.exec();
}

mycass.h：

#ifndef MYCLASS_H
#define MYCLASS_H
#include <QDebug>
#include <QString>
#include <QList>

class MyClass : public QObject
{
    Q_OBJECT
public:
    MyClass(QObject *parent = 0);

    Q_INVOKABLE void cppSlot(QVariant msg);
};
#endif // MYCLASS_H

myclass.cpp：

#include "myclass.h"

MyClass::MyClass(QObject *parent):QObject(parent){}

void MyClass::cppSlot(QVariant msg)
{
    qDebug() << "c++: bien reçu chef " << msg;
}

ma​​in.qml:

import QtQuick 2.4
import QtQuick.Layouts 1.1
import Material.ListItems 0.1 as ListItem
import Material.Extras 0.1
import QtQuick.Controls 1.3 as QuickControls
import QtQuick.Controls 1.4
import Material 0.2

Window 
{
    visible: true
    property var listCloud: ["nuage1", "nuage2", "nuage3", "nuage4"]
    id: item
    width: 100; height: 100

    Rectangle
    {
        id:sousRect
        color:"red"
        width:100; height:100

        Button
        {
            id:buttonTest
            onClicked: myobject.cppSlot(listCloud)
        }
    }
} 

但如果你喜欢使用 SIGNAL SLOTS，QML 中有 Connections Object。您的 main.qml 将如下所示：

Window 
{
    visible: true
    property var listCloud: ["nuage1", "nuage2", "nuage3", "nuage4"]
    id: item
    width: 100; height: 100

    Connections
    {
        target: buttonTest
        onClicked: myobject.cppSlot(listCloud)
    }

    Rectangle
    {
        id:sousRect
        color:"red"
        width:100; height:100

        Button
        {
            id:buttonTest
        }
    }
}

Q_INVOKABLE 不是别的公共SLOT，它会通过元对象系统调用。