Figure 2. Designer shows off the form for our application. Figure 1. Designer lets you easily create forms with widgets, including WebKit.
QtWebKit provides developers with a handful of useful classes. At the very top level, there is QWebView, which is a QWidget with a number of convenience functions, such as setUrl(), loadProgress() and reload(). Inside Qt Designer, the GUI builder for Qt applications, you even can drag a QWebView into a form and set the URL. QWebView is built on top of QWebPage, which contains the Web content, history and settings. QWebPage is not a widget, but was built to be used on many surfaces, including QGraphicsView, Qt’s canvas widget. Supporting QWebView and QWebPage are classes that let you build plugins, access the page history and walk the frames. A lot of the fun of having WebKit in your application is having it pull content from the Internet. Qt 4.4.0 introduces new networking classes, including an all new HTTP implementation. QNetworkAccessManager handles all network requests and replies with support for HTTP 1.0, 1.1 and SSL. A custom cookie jar and proxy configuration also can be set. Qt’s source code includes a demo browser and example applications that show off how to use many of the features of these classes. Qt always has provided fantastic cross-platform support with integration into the desktop. With the introduction of QtWebKit, developers now can make a cross-platform desktop application for a Web site. Linux Journal provides a digital subscription that lets you download older issues. The Web site is very simple and a perfect candidate for building a small application around. Although the Web site does have the table of contents, it does not provide a way to search all the available issues for articles. So the application I am going to make provides an easy way to search through the issues and let you download them. The GUI for the application was made with Qt Designer and has a matching main window class that contains the functionality. To compile the project, Qt includes a cross-platform build tool called qmake. Beyond the normal qmake template when using QtWebKit, the Qt variable also needs WebKit to be specified for the library to be linked in. Our application’s project file (lj.pro) consists of the following:
TEMPLATE = app QT += WebKit FORMS += lj.ui SOURCES += main.cpp mainwindow.cpp HEADERS += mainwindow.h
Like most Qt applications, main.cpp contains only a small amount of code. It constructs a QApplication and the main window, and then starts the event loop. By setting the application name, we tell QtWebKit to include it in the user agent string automatically. That way, if Qt’s networking in your application starts behaving badly, Web site developers know whom to contact. The user agent string is, of course, fully customizable by subclassing QWebPage if you need to. Here’s the main.cpp file: #include <qapplication.h> #include "mainwindow.h" int main(int argc, char **argv) { QApplication app(argc, argv); app.setApplicationName("LinuxJournalDigital"); MainWindow mainwindow; mainwindow.show(); return app.exec(); }
The interface was built in just a few minutes using Qt Designer. On the left-hand side are two QListViews. The one on the top will contain the list of available issues, and the bottom one will contain the table of contents of the currently selected issue. On the right-hand side is a QWebView. The interface file is turned into a header file (ui_lj.h) by uic during the compilation process. ui_lj.h contains the generated Ui_Form class along with all the objects in the interface. The main window class definition is a subclass of QMainWindow and Ui_Form. The only new objects in the MainWindow classes are the models that are used to contain the list of issues w w w. l i n u x j o u r n a l . c o m july 2008 | 55