在 C++ 中获取 ApplicationWindow 的大小

Question

如何在 C++ 中获取 QML ApplicationWindow 的大小？

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

if (engine.rootObjects().isEmpty())
    return -1;

QObject *application_object = engine.rootObjects().first();

// Throws ApplicationWindow_QMLTYPE_11::height(int), no such signal
QObject::connect(application_object, SIGNAL(height(int)), &my_obj_here, SLOT(set_game_height(int)));
QObject::connect(application_object, SIGNAL(width(int)), &my_obj_here, SLOT(set_game_width(int)));

return app.exec();

我意识到我也没有获取 ApplicationWindow 内容的大小（减去工具栏、菜单栏等），但我如何访问它？

正在尝试使用 property 方法 returns 空指针访问 window_object 上的 window 属性。

Answer 1

一个可能的解决方案是用QQmlProperty获取QQuickItem，然后连接信号heightChanged和widthChanged，这些信号只通知属性变了但不表示值，所以必须用height()和width().

的方法

QObject *topLevel = engine.rootObjects().first();
QQuickItem *contentItem =qvariant_cast<QQuickItem *>(QQmlProperty::read(topLevel, "contentItem"));
if(contentItem){
    QObject::connect(contentItem, &QQuickItem::heightChanged,
                     [&my_obj_here, contentItem](){
        my_obj_here.set_game_height(contentItem->height());
    });
    QObject::connect(contentItem, &QQuickItem::widthChanged, 
                     [&my_obj_here, contentItem](){
        my_obj_here.set_game_width(contentItem->width());
    });
}

另一个解决方案是在 QML 端建立连接，为此您必须创建 q-property:

class GameObject: public QObject{
    Q_OBJECT
    Q_PROPERTY(int game_width READ game_width WRITE set_game_width NOTIFY game_widthChanged)
    Q_PROPERTY(int game_height READ game_height WRITE set_game_height NOTIFY game_heightChanged)
public:
    using QObject::QObject;
    int game_width() const{
        return m_width;
    }
    void set_game_width(int width){

        if(width == m_width)
            return;
        m_width = width;
        emit game_widthChanged();
    }
    int game_height() const{
        return m_height;
    }
    void set_game_height(int height){
        if(height == m_height)
            return;
        m_height = height;
        emit game_heightChanged();
    }
signals:
    void game_widthChanged();
    void game_heightChanged();
private:
    int m_width;
    int m_height;
};

main.cpp

...
GameObject my_obj_here;

QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("my_obj_here", &my_obj_here);
...

main.qml

ApplicationWindow{


    Connections{
        target: contentItem
        onHeightChanged:
            my_obj_here.game_height = height
        onWidthChanged:
            my_obj_here.game_width = width
    }
    ...

在 C++ 中获取 ApplicationWindow 的大小

Get Size of ApplicationWindow in C++

c++

qt

applicationwindow

qml

qt5