如何从 C++ 设置 QML 属性

Question

I'm trying to do a simple task as changing a property (text: ) of some QML object from C++ yet I'm failing miserably. Any help appreciated.

I'm not getting any errors, the window shows up, just the text property doesn't change as (at least I think) it should. Is even anything I'm NOT doing wrong here?!!

What I was trying is this:

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickView>
#include <QQuickItem>
#include <QQmlEngine>
#include <QQmlComponent>
#include <QString>

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

    QQmlApplicationEngine engine;


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

     engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    QString thisString = "Dr. Perry Cox";

    object->setProperty("text", thisString);  //<--- tried  instead of thisString putting "Dr. ..." but nope.
    delete object;



    return app.exec();
}

main.qml

import QtQuick 2.2
import QtQuick.Window 2.1

Window {
    visible: true
    width: 360
    height: 360

    MouseArea {
        anchors.fill: parent
        onClicked: {
            Qt.quit();
        }
    }

    Text {
        id: whot
        text: ""
        anchors.centerIn: parent
        font.pixelSize: 20
        color: "green"
    }
}

Answer 1

When you call QObject *object = component.create(); you get access to the root context, which is the Window component and its properties.

To get access to Text properties, you can create property alias like this:

Window {
    property alias text: whot.text
    ...
    Text {
        id: whot
        text: ""
        ...
    }
}

That will give you access to whot 's text property from within the Window 's context.

There is another slightly more round-about way. Assign objectName property instead of id (or both if you still need id ) to whot :

Text {
    id: whot // <--- optional
    objectName: "whot" // <--- required
    text: ""
    ...
 }

Now you can do this in code:

QObject *whot = object->findChild<QObject*>("whot");
if (whot)
    whot->setProperty("text", thisString);

On a side note: I don't think you are supposed to delete the object until after calling app.exec() . Otherwise, it will ... well, be deleted. :)

Answer 2

#include <QQmlContext>
#include <qquickview.h>
#include <qdir.h>

QQmlApplicationEngine engine;
QString root = QCoreApplication::applicationDirPath();
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
        return -1;
QObject *topLevel = engine.rootObjects().value(0);
QQuickWindow *window = qobject_cast<QQuickWindow*>(topLevel);
window->setProperty("root", root);

for qml

ApplicationWindow  {
    property string root
    onRootChanged: {
        console.log("root : "+ root);
    }
}

Answer 3

对于 QML 属性，您应该改用QQmlProperty ：

QQmlProperty::write(whot, "text", thisString);