Save and load QWebEngineHistory to a QWebEnginePage

Question

I need to save the history of a QWebEnginePage and load it back. Therefore I want to store the history from page A in some structure and set it to page B.

In the documentation I found the following methods:

// Saves the web engine history history into stream.
QDataStream &operator<<(QDataStream &stream, const QWebEngineHistory &history)

// Loads the web engine history from stream into history.
QDataStream &operator>>(QDataStream &stream, QWebEngineHistory &history)

But honestly I don't know how to work with them. I tried the following:

QWebEnginePage *m_history;
...
...
void setHistory(QWebEngineHistory *history){
   QDataStream data;
   data << history; //Hoping that the content of data is persistent after deleting of the QWebEnginePage where the history is coming from
   data >> m_history;
}

And later on I want to load it back to the page:

m_history >> m_webEnginePage.history(); // Pseudo-Code

I know that the QWebEngineHistory of a QWebEnginePage is const, but then I'm wondering why are there even those two methods from above? Why is there a function that "loads the web engine history into history"?

The only alternative I can think of is storing my history in a QList, but managing this is not nice and could lead to more problems (because of the whole forward/backward button etc).

Thank you very much for your help.

eyllanesc · Accepted Answer · 2019-12-03T11:45:54.663

No object can be saved, what is saved is the information associated with the object so you should not create QWebEngineHistory but save and/or load the information.

In the following example, the information is saved in a file when the application is closed and the startup is loaded.

#include <QtWebEngineWidgets>

int main(int argc, char *argv[]) {
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QApplication app(argc,argv);

    const QString filename = "history.bin";

    QWebEngineView view;
    view.load(QUrl("https://stackoverflow.com"));

    {// load
        QFile file(filename);
        if(file.open(QFile::ReadOnly)){
            qDebug() << "load";
            QDataStream ds(&file);
            ds >> *(view.page()->history());
        }
    }  

    view.resize(640, 480);
    view.show();

    int ret = app.exec();

    {// save
        QFile file(filename);
        if(file.open(QFile::WriteOnly)){
            qDebug() << "save";
            QDataStream ds(&file);
            ds << *(view.page()->history());
        }
    }  

    return ret;
}

In the same way you can save it through QSettings:

#include <QtWebEngineWidgets>

int main(int argc, char *argv[]) {
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QApplication app(argc,argv);

    QWebEngineView view;
    view.load(QUrl("https://stackoverflow.com"));

    {// load
        QSettings settings;
        QByteArray ba = settings.value("page/history").toByteArray();
        QDataStream ds(&ba, QIODevice::ReadOnly);
        ds >> *(view.page()->history());
    }  

    view.resize(640, 480);
    view.show();

    int ret = app.exec();

    {// save
        QSettings settings;
        QByteArray ba;
        QDataStream ds(&ba, QIODevice::WriteOnly);
        ds << *(view.page()->history());
        settings.setValue("page/history", ba);
    } 

    return ret;
}

First of all thank you very much for your detailed information! — Vanessa, Dec 03 '19 at 13:01
I was posting my comment too early and can't edit it anymore... So again: Thank you very very much for your detailed information! It really solved my problem and helped me a lot understanding it :) I was looking a long time why it was not working, until I found out that I forgot the dereference for ds << *(view.page()->history());... Thanks again! — Vanessa, Dec 03 '19 at 13:20

Save and load QWebEngineHistory to a QWebEnginePage

1 Answers1