Searching for XML attributes with special parent in with Qt

Question

How can I manage that my XML reader, searching for attributes with a special parent element?

e.g. my XML file:

    <section name="aPoly">
        <attribute key="id" type="int">1</attribute>
        <attribute key="label" type="String">2</attribute>
        <section name="graphic">
            <attribute key="x" type="double">780.0</attribute>
            <attribute key="y" type="double">240.0</attribute>
            <attribute key="w" type="double">78.0</attribute>
            <attribute key="h" type="double">78.0</attribute>
        </section>
    </section>
    ...
    ...
    <section name="line">
        <attribute key="source" type="int">0</attribute>
        <attribute key="target" type="int">4</attribute>
        <section name="graphic">
            <attribute key="fill" type="String">#000000</attribute>
            <section name="poly">
                <section name="pt">
                    <attribute key="x" type="double">377.0</attribute>
                    <attribute key="y" type="double">240.0</attribute>
                </section>
                <section name="pt">
                    <attribute key="x" type="double">570.0</attribute>
                    <attribute key="y" type="double">240.0</attribute>
                </section>
                <section name="pt">
                    <attribute key="x" type="double">570.0</attribute>
                    <attribute key="y" type="double">330.0</attribute>
                </section>
            </section>
        </section>
    </section>

There are multiple attributes with key = "x". I want to save the x values of section name="aPoly" in one array and the x values of section name="line" into another array.

I am searching for attributes and save it to a QVector. (Search all X attributes).

  QDomElement root = document.documentElement();
  QDomNodeList key = root.elementsByTagName("attribute");
   for(int i = 0; i < key.count(); i++)
{

    QDomNode keynode = key.at(i);
    if(keynode.isElement())
    {
        QDomElement att = keynode.toElement();

        if (att.attribute("key") == "x"){

            xarray.push_back(att.text());

        }else if (att.attribute("key") =="y") {

            yarray.push_back(att.text());

        }...

What can I change to achieve this?

Edit:

Why he dont fill my array? Its always empty? Where is my mistake?

 QXmlQuery query;
if (query.setFocus(&file))
{
    query.setQuery(QString("section/section/section[@name='aPoly']/section/attribute[@key='x']"));
    if (query.isValid())
    {
        QString result;
        query.evaluateTo(&result);
        QDomDocument dom;
        dom.setContent(QString("<Data>%1</Data>").arg(result));
        QDomNodeList children = dom.documentElement().childNodes();
        for (int i = 0; i < children.count(); i++)
        {
            QDomNode nod = children.at(i);

            if(nod.isElement())
            {
            QDomElement art = nod.toElement();
            Newarray.push_back(art.text());
            }
        }

    }
}
  qDebug() << "\r\nNewArray : " <<QList<QString>::fromVector(Newarray);

Answer 1

You can use XQuery for this. XPath similar to following can be used for your purpose assuming section elements are inside a sections element and it is the root of your xml document.

"sections/section[@name='aPoly']/attribute[@key='x']"

Eg.

QXmlQuery query;
if (query.setFocus(yourXmlString)
{
    query.setQuery("sections/section[@name='aPoly']/attribute[@key='x']");
    if (query.isValid())
    {
        QString result;
        query.evaluateTo(&result);
        QDomDocument dom;
        dom.setContent(QString("<Data>%1</Data>").arg(result));
        QDomNodeList children = dom.documentElement().childNodes();
        for (int i = 0; i < children.count(); ++i) 
        {
            //children.at(i) is an attribute element which matches your criteria.
        }
    }
}