<?xml version="1.0" encoding="UTF-8"?>
<Parameters>
<para1>1</para1>
<para2>2</para2>
<para3>3</para3>
</Parameters>

void QtMainWindow::on_actionSave_triggered() {
QString filename = QFileDialog::getSaveFileName(this,
tr("Save Xml"), ".",
tr("Xml files (*.xml)"));
QFile file(filename);
file.open(QIODevice::WriteOnly);
QXmlStreamWriter xmlWriter(&file);
xmlWriter.setAutoFormatting(true);
xmlWriter.writeStartDocument();
xmlWriter.writeStartElement("Parameters");
xmlWriter.writeTextElement("para1",QString::number(1));
xmlWriter.writeTextElement("para2",QString::number(2));
xmlWriter.writeTextElement("para3",QString::number(3));
xmlWriter.writeEndElement();
xmlWriter.writeEndDocument();
file.close();
}

void QtMainWindow::on_actionLoad_triggered() {
    QString filename = QFileDialog::getOpenFileName(this,
        tr("Open Xml"), ".",
        tr("Xml files (*.xml)"));
    QFile file(filename);
    if (!file.open(QFile::ReadOnly | QFile::Text)) {
        std::cerr << "Error: Cannot read file " << qPrintable(filename)
            << ": " << qPrintable(file.errorString())
            << std::endl;
    }
    QXmlStreamReader xmlReader(&file);
    xmlReader.readNext();
    while(!xmlReader.atEnd()) {
        if(xmlReader.isStartElement()) {
            if(xmlReader.name() == "Parameters") {
                xmlReader.readNext();
            } else if (xmlReader.name() == "para1") {
                int para1 = xmlReader.readElementText().toInt();
                xmlReader.readNext();
            } else if (xmlReader.name() == "preFilterCap") {
                int para2 = xmlReader.readElementText().toInt();
                xmlReader.readNext();
            } else if (xmlReader.name() == "SADWindowSize") {
                int para3 = xmlReader.readElementText().toInt();
                xmlReader.readNext();
            } else {
                xmlReader.raiseError(QObject::tr("Not a options file"));
            }
        } else {
            xmlReader.readNext();
        }
        file.close();
        if (xmlReader.hasError()) {
            std::cerr << "Error: Failed to parse file "
                << qPrintable(filename) << ": "
                << qPrintable(xmlReader.errorString()) << std::endl;
        } else if (file.error() != QFile::NoError) {
            std::cerr << "Error: Cannot read file " << qPrintable(filename)
                << ": " << qPrintable(file.errorString())
                << std::endl;
        }
    }
}