Come posso utilizzare QXMLQuery QT per eseguire query XPath su un file locale?

Question

Sto cercando di afferrare le coordinate da file .kml che sembrano qualcosa del genere:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.0">
    <Document>
        <name>Name</name><Style id="roadStyle"><LineStyle><color>7fcf0064</color><width>6</width></LineStyle></Style><Snippet><![CDATA[<font size=+1><a href="http://example.com/">Printable view</a></font>]]></Snippet>
        <Placemark>
            <name>Example</name>
            <description><![CDATA[example]]></description><address>100 Example St</address><StyleMap><Pair><key>normal</key><Style><IconStyle><Icon><href>http://example.com</href></Icon><hotSpot x="0.000000" y="0.000000" xunits="fraction" yunits="fraction" /></IconStyle><ListStyle><ItemIcon><href>http://example.com</href></ItemIcon></ListStyle></Style></Pair><Pair><key>highlight</key><Style><IconStyle><scale>1.000000</scale><Icon><href>http://example.com</href></Icon><hotSpot x="0.000000" y="0.000000" xunits="fraction" yunits="fraction" /></IconStyle><ListStyle><ItemIcon><href>http://example.com</href></ItemIcon></ListStyle></Style></Pair></StyleMap><Point><coordinates>0.000000,0.000000,0</coordinates></Point><LookAt><longitude>0.000000</longitude><latitude>0.000000</latitude><range>100.000000</range><tilt>45.000000</tilt><heading>0.000000</heading></LookAt>
        </Placemark>
        <Placemark>
            <name>Route</name>
            <description><![CDATA[Example]]></description>
            <GeometryCollection>
                <LineString>
                    <coordinates>0.000000,0.000000,0.000000 0.000000,0.000000,0.000000 0.000000,0.000000,0.000000 0.000000,0.000000,0.000000 0.000000,0.000000,0.000000 0.000000,0.000000,0.000000 0.000000,0.000000,0.000000</coordinates>
                </LineString>
            </GeometryCollection>
            <styleUrl>#roadStyle</styleUrl>
        </Placemark>
    </Document>
</kml>

.

Sto cercando di usare qxmlquery per recuperare le coordinate con una stringa XPath simile a questo:

kml/Document/Placemark[last()]/GeometryCollection/LineString/coordinates

.

Ho testato che qui e confermato funziona, finora così bene.Ma ho avuto un orribile tempo a farlo funzionare in Qt.Ho provato molte cose, compresi i suggerimenti in altri post qui su così, senza fortuna.Ecco un coppia esempi che mostrano le variazioni:

void testQuery1(QString &filename) {
    QXmlQuery query;
    query.bindVariable("kmlFile", QVariant(filename));
    query.setQuery("declare default element namespace \"http://earth.google.com/kml/2.0\"; declare variable $kmlFile external; doc($kmlFile)//coordinates");

    QStringList results;
    query.evaluateTo(&results);

    qDebug() << results.size();
}

void testQuery2(QString &filename) {
    QFile file(filename);
    file.open(QIODevice::ReadOnly);

    QXmlQuery query;
    query.setFocus(&file);
    query.setQuery("kml/Document/Placemark[last()]/GeometryCollection/LineString/coordinates");

    QString result;
    query.evaluateTo(&result);

    qDebug() << result;
}

.

Io ottengo 0 e " \n" da ciascuno di quelli, rispettivamente.Dove sto andando male qui e cosa devo fare per risolverlo?Sono aperto ad altri approcci finché rimangono all'interno di QT (sto usando 4.7) e standard C ++.

Answer 1

Dopo molte sperimentazioni, mi sembra di aver colpito la ricetta magica:

void testQuery(QString &filename) {
    QFile file(filename);
    file.open(QIODevice::ReadOnly);

    QXmlQuery query;
    query.bindVariable("kmlFile", &file);
    query.setQuery("declare default element namespace \"http://earth.google.com/kml/2.0\"; declare variable $kmlFile external; doc($kmlFile)/kml/Document/Placemark[last()]/GeometryCollection/LineString/coordinates/text()");

    QString result;
    query.evaluateTo(&result);

    qDebug() << result;

    file.close();
}

.

che mi dà la mia stringa di zero (o qualunque sia la coordinata).