Come posso utilizzare QXMLQuery QT per eseguire query XPath su un file locale?
Domanda
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 ++.
Soluzione
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).