问QXmlQuery和Xpath :不能提取节点的文本或参数的值

EN

#include <QApplication>
#include <QFile>
#include <QDebug>
#include <QXmlQuery>
#include <QXmlSerializer>
#include <QXmlFormatter>
#include <QBuffer>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QString xmlContent =
            "<nodes>"
                "<node1 param='x1'>"
                    "<value>text1</value>"
                "</node1>"
                "<node2 param='x2'>"
                    "<value>text2</value>"
                "</node2>"
            "</nodes>";

    QBuffer device;
    device.setData(QByteArray(xmlContent.toUtf8().constData()));
    device.open(QIODevice::ReadOnly);

    QXmlQuery query;
    query.bindVariable("inputDocument", &device);

    // Extracting "text1"
    query.setQuery(QString("doc($inputDocument)/nodes/node1/value[text()]"));

    // Exracting "x1"
    //query.setQuery(QString("doc($inputDocument)/nodes/node1/@param"));

    // Output value
    QByteArray outArray;
    QBuffer buffer(&outArray);
    buffer.open(QIODevice::ReadWrite);

    QXmlSerializer serializer(query, &buffer);
    query.evaluateTo(&serializer);

    buffer.close();
    qWarning() << "Exracted value : " << QString::fromUtf8(outArray.constData());

    exit(0);

    return a.exec(&#41;;
}