- Qt 5.5
- Qt WebEngine Widgets
- Porting from Qt WebKit to Qt WebEngine
- Qt 5.5.1 Reference Documentation

# Porting from Qt WebKit to Qt WebEngine

This provides rough steps to follow when porting an application using Qt WebKit's QWebView API to use Qt WebEngine's QWebEngineView.

## Class Names

The Qt WebEngine equivalent of Qt WebKit C++ classes are prefixed by "QWebEngine" instead of "QWeb".

Qt WebKit

    #include <QWebHistory>
    #include <QWebHistoryItem>
    #include <QWebPage>
    #include <QWebView>

    QWebHistory
    QWebHistoryItem
    QWebPage
    QWebView

Qt WebEngine

    #include <QWebEngineHistory>
    #include <QWebEngineHistoryItem>
    #include <QWebEnginePage>
    #include <QWebEngineView>

    QWebEngineHistory
    QWebEngineHistoryItem
    QWebEnginePage
    QWebEngineView

## Qt Module Name

### In qmake Project Files

Qt WebKit

    QT += webkitwidgets

Qt WebEngine

    QT += webenginewidgets

### Including the Module in Source Files

Qt WebKit

    #include <QtWebKit/QtWebKit>
    #include <QtWebKitWidgets/QtWebKitWidgets> // With Qt >= 4.8

Qt WebEngine

    #include <QtWebEngineWidgets/QtWebEngineWidgets>

## QWebFrame has been Merged into QWebEnginePage

It is not possible to access sub-frames. Methods of the main QWebFrame are now available directly through the QWebEnginePage itself.

Qt WebKit

    QWebPage page;
    connect(page.mainFrame(), SIGNAL(urlChanged(const QUrl&)), SLOT(mySlotName()));
    page.mainFrame()->load(url);

Qt WebEngine

    QWebEnginePage page;
    connect(&page, SIGNAL(urlChanged(const QUrl&)), SLOT(mySlotName()));
    page.load(url);

## Some methods now return their result asynchronously

Since Qt WebEngine uses a multi-process architecture, applications needs to return to the event loop where the result will be received asynchronously from Qt WebEngine's render process. A function pointer, a functor or a lambda expression must be provided to handle the result when it is available.

Qt WebKit

    QWebPage *page = new QWebPage;
    QTextEdit *textEdit = new QTextEdit;
    // *textEdit is modified immediately.
    textEdit->setPlainText(page->toHtml());
    textEdit->setPlainText(page->toPlainText());

Qt WebEngine (with a lambda function in C++11)

    QWebEnginePage *page = new QWebEnginePage;
    QTextEdit *textEdit = new QTextEdit;
    // *textEdit must remain valid until the lambda function is called.
    page->toHtml([textEdit](const QString &result){ textEdit->setPlainText(result); });
    page->toPlainText([textEdit](const QString &result){ textEdit->setPlainText(result); });

Qt WebEngine (with a functor template wrapping a member function)

    template<typename Arg, typename R, typename C>
    struct InvokeWrapper {
        R *receiver;
        void (C::*memberFun)(Arg);
        void operator()(Arg result) {
            (receiver->*memberFun)(result);
        }
    };

    template<typename Arg, typename R, typename C>
    InvokeWrapper<Arg, R, C> invoke(R *receiver, void (C::*memberFun)(Arg))
    {
        InvokeWrapper<Arg, R, C> wrapper = {receiver, memberFun};
        return wrapper;
    }

    QWebEnginePage *page = new QWebEnginePage;
    QTextEdit *textEdit = new QTextEdit;
    // *textEdit must remain valid until the functor is called.
    page->toHtml(invoke(textEdit, &QTextEdit::setPlainText));
    page->toPlainText(invoke(textEdit, &QTextEdit::setPlainText));

Qt WebEngine (with a regular functor)

    struct SetPlainTextFunctor {
        QTextEdit *textEdit;
        SetPlainTextFunctor(QTextEdit *textEdit) : textEdit(textEdit) { }
        void operator()(const QString &result) {
            textEdit->setPlainText(result);
        }
    };

    QWebEnginePage *page = new QWebEnginePage;
    QTextEdit *textEdit = new QTextEdit;
    // *textEdit must remain valid until the functor is called.
    page->toHtml(SetPlainTextFunctor(textEdit));
    page->toPlainText(SetPlainTextFunctor(textEdit));

## Qt WebEngine does not Interact with QNetworkAccessManager

Some classes of Qt Network such as QAuthenticator were reused for their interface but, unlike Qt WebKit, Qt WebEngine has its own HTTP implementation and can't go through a QNetworkAccessManager.

Signals and methods of QNetworkAccessManager that are still supported were moved to QWebEnginePage directly.

Qt WebKit

    QNetworkAccessManager qnam;
    QWebPage page;
    page.setNetworkAccessManager(&qnam);
    connect(&qnam, SIGNAL(authenticationRequired(QNetworkReply*,QAuthenticator*)), this, SLOT(authenticate(QNetworkReply*,QAuthenticator*)));

Qt WebEngine

    QWebEnginePage page;
    connect(&page, SIGNAL(authenticationRequired(QNetworkReply*,QAuthenticator*)), this, SLOT(authenticate(QNetworkReply*,QAuthenticator*)));

## Notes about Individual Methods

### evaluateJavaScript

QWebFrame::evaluateJavaScript was renamed and moved as QWebEnginePage::runJavaScript. It is currently only possible to run JavaScript on the main frame of a page and the result is returned asynchronously to the provided functor.

Qt WebKit

    QWebPage *page = new QWebPage;
    qDebug() << page->mainFrame()->evaluateJavaScript("'Java' + 'Script'");

Qt WebEngine (with lambda expressions in C++11)

    QWebEnginePage *page = new QWebEnginePage;
    page->runJavaScript("'Java' + 'Script'", [](const QVariant &result){ qDebug() << result; });

### setHtml and setContent

QWebEnginePage::setHtml and QWebEnginePage::setContent perform asynchronously the same way as a normal HTTP load would, unlike their QWebPage counterparts.

### setContentEditable

QWebPage::setContentEditable has no equivalent since any document element can be made editable through the contentEditable attribute in the latest HTML standard. Therefore, QWebEnginePage::runJavaScript is all that is needed.

Qt WebKit

    QWebPage page;
    page.setContentEditable(true);

Qt WebEngine

    QWebEnginePage page;
    page.runJavascript("document.documentElement.contentEditable = true");

## Unavailable Qt WebKit APIs

Qt WebKit classes and methods in this list will not be available in Qt WebEngine.

QGraphicsWebView | Qt WebEngine requires hardware acceleration. Since we couldn't support a web view class in a QGraphicsView unless it is attached to a QGLWidget viewport, this feature is out of scope.
QWebElement | Qt WebEngine uses a multi-process architecture and this means that any access to the internal structure of the page has to be done asynchronously, any query result must be returned through callbacks. The QWebElement API was designed for synchronous access and this would require a complete redesign.
QWebDatabase | The Web SQL Database feature that this API was wrapping in Qt WebKit was dropped from the HTML5 standard.
QWebPluginFactory, QWebPage::setPalette, QWebView::setRenderHints | Qt WebEngine renders web pages using Skia and isn't using QPainter or Qt for this purpose. The HTML5 standard also now offers much better alternatives that were not available when native controls plugins were introduced in Qt WebKit.
QWebHistoryInterface | Visited links are persisted automatically by Qt WebEngine.