Porting from Qt WebKit to Qt WebEngine#
Overview of the differences between the Qt WebKit and Qt WebEngine API.
The following sections contain information about porting an application that uses the Qt WebKit QWebView API to use the Qt WebEngine QWebEngineView
.
Architecture#
Chromium provides its own network and painting engines, which Qt WebEngine uses. This, among other things, allows Qt WebEngine to provide better and more reliable support for the latest HTML5 specification than Qt WebKit. However, Qt WebEngine is thus also heavier than Qt WebKit and does not provide direct access to the network stack and the HTML document through C++ APIs.
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#
HTML frames can be used to divide web pages into several areas where the content can be represented individually.
In Qt WebKit, QWebFrame represents a frame inside a web page. Each QWebPage object contains at least one frame, the main frame, obtained using QWebPage::mainFrame(). Additional frames will be created for the HTML <frame>
element, which defines the appearance and contents of a single frame, or the <iframe>
element, which inserts a frame within a block of text.
In Qt WebEngine, frame handling has been merged into the QWebEnginePage
class. All child frames are now considered part of the content, and only accessible through JavaScript. Methods of the QWebFrame class, such as load()
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#
Because Qt WebEngine uses a multi-process architecture, calls to some methods from applications will return immediately, while the results should be received asynchronously via a callback mechanism. A function pointer, a functor, or a lambda expression must be provided to handle the results when they become 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 cannot go through a QNetworkAccessManager.
The signals and methods of QNetworkAccessManager that are still supported were moved to the QWebEnginePage
class.
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*)));
Note
In Qt WebEngine, the QAuthenticator must be explicitly set to null to cancel authentication:
*authenticator = QAuthenticator();
Omitting the QNetworkAccessManager
also affects the way in which certificates are managed. For more information, see Managing Certificates .
Notes About Individual Methods#
evaluateJavaScript#
QWebFrame::evaluateJavaScript was moved and renamed as 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#
setHtml
and 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, runJavaScript
is all that is needed.
Qt WebKit
QWebPage page; page.setContentEditable(true);
Qt WebEngine
QWebEnginePage page; page.runJavaScript("document.documentElement.contentEditable = true");