C++和QML之间的通信

Question

此页面显示如何从QML中调用C++函数.

我想要做的是通过C++函数更改Button上的图像(触发状态更改或者完成它).

我怎样才能做到这一点？

UPDATE

我尝试了Radon的方法,但是当我插入这一行时:

    QObject *test = dynamic_cast<QObject *>(viewer.rootObject());

编译器抱怨这样:

    error: cannot dynamic_cast '((QMLCppBinder*)this)->QMLCppBinder::viewer.QDeclarativeView::rootObject()' (of type 'struct QGraphicsObject*') to type 'class QObject*' (source is a pointer to incomplete type)

如果它是相关的,QMLCppBinder是我尝试构建的类,用于封装从几个QML页面到C++代码的连接.这似乎比人们预期的更棘手.

这是一个骨架类,为此提供一些上下文:

    class QMLCppBinder : public QObject
    {
        Q_OBJECT
    public:
        QDeclarativeView viewer;

        QMLCppBinder() {
            viewer.setSource(QUrl("qml/Connect/main.qml"));
            viewer.showFullScreen();
            // ERROR
            QObject *test = dynamic_cast<QObject *>(viewer.rootObject());
        }
    }

Answer 1

如果您objectName为图像设置了一个,您可以很容易地从C++访问它:

main.qml

import QtQuick 1.0

Rectangle {
    height: 100; width: 100

    Image {
        objectName: "theImage"
    }
}

在C++中:

// [...]

QDeclarativeView view(QUrl("main.qml"));
view.show();

// get root object
QObject *rootObject = dynamic_cast<QObject *>(view.rootObject());

// find element by name
QObject *image = rootObject->findChild<QObject *>(QString("theImage"));

if (image) { // element found
    image->setProperty("source", QString("path/to/image"));
} else {
    qDebug() << "'theImage' not found";
}

// [...]

→ QObject.findChild(),QObject.setProperty()

Answer 2

因此,您可以将C++对象设置为C++中QDeclarativeView的上下文属性,如下所示:

QDeclarativeView canvas;
ImageChanger i; // this is the class containing the function which should change the image
canvas.rootContext()->setContextProperty("imgChanger", &i);

在你的ImageChanger班级中,声明一个信号,如:

void updateImage(QVariant imgSrc);

然后,当您想要更改图像时,请致电emit updateImage(imgSrc);.

现在在您的QML中,请按如下方式收听此信号:

Image {
    id: imgToUpdate;
}

Connections {
    target: imgChanger;
    onUpdateImage: {
        imgToUpdate.source = imgSrc;
    }
}

希望这可以帮助.