最小限のRSSリストアプリケーション

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    RSSListing rsslisting(u"https://www.qt.io/blog/rss.xml"_s);
    rsslisting.show();
    return app.exec();
}

class RSSListing : public QWidget
{
    Q_OBJECT
public:
    explicit RSSListing(const QString &url = QString(), QWidget *widget = nullptr);

public slots:
    void fetch();
    void finished(QNetworkReply *reply);
    void consumeData();
    void error(QNetworkReply::NetworkError);

private:
    void parseXml();
    void get(const QUrl &url);

    // Parser state:
    QXmlStreamReader xml;
    QString currentTag;
    QString linkString;
    QString titleString;

    // Network state:
    QNetworkAccessManager manager;
    QNetworkReply *currentReply;

    // UI elements:
    QLineEdit *lineEdit;
    QTreeWidget *treeWidget;
    QPushButton *fetchButton;
};

RSSListing::RSSListing(const QString &url, QWidget *parent)
    : QWidget(parent), currentReply(0)
{
    connect(&manager, &QNetworkAccessManager::finished, this, &RSSListing::finished);

    lineEdit = new QLineEdit(this);
    lineEdit->setText(url);
    connect(lineEdit, &QLineEdit::returnPressed, this, &RSSListing::fetch);

    fetchButton = new QPushButton(tr("Fetch"), this);
    connect(fetchButton, &QPushButton::clicked, this, &RSSListing::fetch);

    treeWidget = new QTreeWidget(this);
    connect(treeWidget, &QTreeWidget::itemActivated,
            // Open the link in the browser:
            this, [](QTreeWidgetItem *item) { QDesktopServices::openUrl(QUrl(item->text(1))); });
    treeWidget->setHeaderLabels(QStringList { tr("Title"), tr("Link") });
    treeWidget->header()->setSectionResizeMode(QHeaderView::ResizeToContents);

    QHBoxLayout *hboxLayout = new QHBoxLayout;
    hboxLayout->addWidget(lineEdit);
    hboxLayout->addWidget(fetchButton);

    QVBoxLayout *layout = new QVBoxLayout(this);
    layout->addLayout(hboxLayout);
    layout->addWidget(treeWidget);

    setWindowTitle(tr("RSS listing example"));
    resize(640, 480);
}

voidRSSListing::fetch() { lineEdit->setReadOnly(true); fetchButton->setEnabled(false); treeWidget->clear(); get(QUrl(lineEdit->text())); }voidRSSListing::consumeData() {intstatusCode=  currentReply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();if(statusCode>= 200 &&statusCode< 300) parseXml(); }voidRSSListing::error(QNetworkReply::NetworkError){
    qWarning("error retrieving RSS feed");
    xml.clear(); currentReply->disconnect(this); currentReply->deleteLater(); currentReply=nullptr; }voidRSSListing::finished(QNetworkReply*reply) { Q_UNUSED(reply); lineEdit->setReadOnly(false); fetchButton->setEnabled(true); }

void RSSListing::get(const QUrl &url)
{
    if (currentReply) {
        currentReply->disconnect(this);
        currentReply->deleteLater();
    }
    currentReply = url.isValid() ? manager.get(QNetworkRequest(url)) : nullptr;
    if (currentReply) {
        connect(currentReply, &QNetworkReply::readyRead, this, &RSSListing::consumeData);
        connect(currentReply, &QNetworkReply::errorOccurred, this, &RSSListing::error);

    }
    xml.setDevice(currentReply); // Equivalent to clear() if currentReply is null.
}

voidRSSListing::parseXml() {while(!xml.atEnd()) { xml.readNext();if(xml.isStartElement()) {if(xml.name()==u"item") { linkString=xml.attributes().value("rss:about").toString(); titleString.clear(); } currentTag=xml.name().toString(); }else if(xml.isEndElement()) {if(xml.name()==u"item") { *item = new item.     QTreeWidgetItem*item = newQTreeWidgetItemitem->setText(0,titleString); item->setText(1,linkString); treeWidget->addTopLevelItem(item); } }else if(xml.isCharacters()&& !xml.isWhitespace()) {if(currentTag== "title") titleString+=xml.text();else if(currentTag== "link") linkString+=xml.text(); } } }if(xml.error()&&xml.error()!= QXmlStreamReader::PrematureEndOfDocumentError)        qWarning() << "XML ERROR:" << xml.lineNumber() << ": " << xml.errorString();
}