QObject的setUserData和setProperty——Qt

QObjectUserData* userData(uint id) const;
void QObject::setUserData(uint id, QObjectUserData* data)
{
    Q_D(QObject);
    if (!d->extraData)
        d->extraData = new QObjectPrivate::ExtraData;
 
    if (d->extraData->userData.size() <= (int) id)
        d->extraData->userData.resize((int) id + 1);
    d->extraData->userData[id] = data;
}
 
 
QVariant property(const char *name) const;
bool QObject::setProperty(const char *name, const QVariant &value)
{
    Q_D(QObject);
    const QMetaObject* meta = metaObject();
    if (!name || !meta)
        return false;
 
    int id = meta->indexOfProperty(name);
    if (id < 0) {
        if (!d->extraData)
            d->extraData = new QObjectPrivate::ExtraData;
 
        const int idx = d->extraData->propertyNames.indexOf(name);
 
        if (!value.isValid()) {
            if (idx == -1)
                return false;
            d->extraData->propertyNames.removeAt(idx);
            d->extraData->propertyValues.removeAt(idx);
        } else {
            if (idx == -1) {
                d->extraData->propertyNames.append(name);
                d->extraData->propertyValues.append(value);
            } else {
                if (value.userType() == d->extraData->propertyValues.at(idx).userType()
                        && value == d->extraData->propertyValues.at(idx))
                    return false;
                d->extraData->propertyValues[idx] = value;
            }
        }
 
        QDynamicPropertyChangeEvent ev(name);
        QCoreApplication::sendEvent(this, &ev);
 
        return false;
    }
    QMetaProperty p = meta->property(id);
#ifndef QT_NO_DEBUG
    if (!p.isWritable())
        qWarning("%s::setProperty: Property \"%s\" invalid,"
                 " read-only or does not exist", metaObject()->className(), name);
#endif
    return p.write(this, value);
}