cpp-access-nested-property.org

在QML中，我常常寫類似這樣的東西：

Item {
    id: settings
    property alias snapshot: snapshot
    Item {
        id: snapshot
        property string saveDirectory: "~/hello/world/"
  }
}

這樣就可以透過 settings.snapshot.saveDirectory 來存取資料，但想要用C++做類似的事情遇到問題了orz

state.cpp

// =============================================================
/// Settings為根項目

class Settings : public QObject
{
    Q_OBJECT
    Q_PROPERTY(SnapshotSettings* snapshot READ snapshot)  // <- this property is a pointer! very important!
public:
    explicit Settings(QObject *parent=0) : m_snapshot_settings(new SnapshotSettings) {}
private:
    SnapshotSettings* m_snapshot_settings;
}

// =============================================================

class SnapshotSettings : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString saveDirectory READ saveDirectory)
public:
    explicit Settings(QObject *parent=0) : m_save_directory("~/hello/world/") {}
private:
    QUrl m_save_directory;
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQml>
#include <QQmlContext>
#include "state.cpp"

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

    Settings settings;
    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("settings", &settings);
    engine.addImportPath(QStringLiteral(":/qml"));
    engine.load(QUrl("qrc:/qml/main.qml"));

    return app.exec();
}

但這樣沒辦法在QML中存取到 settings.snapshot.saveDirectory ，會說

QMetaProperty::read: Unable to handle unregistered datatype 'SnapshotSettings' for property 'Settings::snapshot'
main.qml:52: TypeError: Cannot read property saveDirectory' of undefined

，所以我幹了這樣的事情：

// #include balabala....
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    Settings settings;
    QQmlApplicationEngine engine;

    qRegisterMetaType<SnapshotSettings*>("SnapshotSettings");        // added

    engine.rootContext()->setContextProperty("settings", &settings);
    engine.addImportPath(QStringLiteral(":/qml"));
    engine.load(QUrl("qrc:/qml/main.qml"));

    return app.exec();
}

現在可以用了，但沒辦法自動補全到第二層。就是我輸入 settings. QtCreator 能夠跳出 snapshot ，但 saveDirectory 就跳不出來了。不知有沒有大大對此問題有解。

kuanyui/cpp-access-nested-property.org

state.cpp

main.cpp