Dr. Dobb's Journal - June 2008 - (Page 30)

d06espen_p4ds 4/11/08 9:15 AM Page 30 Core Technology by Espen Riskedal Qt and Windows CE A cross-platform C++ framework for mobile devices Qt is a C++ application framework from Trolltech that lets you write native applications that Espen is a senior software engineer for Trolltech. He can be contacted at espenr@ trolltech.com. can be compiled cross-platform. This means that the source code only needs to be written once, yet support Linux, Windows CE/98/XP/Vista, Mac OS X, UNIX, and Embedded Linux. To deploy, you simply compile it for your target platform. One well-known application taking advantage of this kind of capability is Google Earth, which is available for Linux, Windows, and Mac OS X. Qt makes it easy for Google to maintain its code base and simultaneously support several platforms. When it comes to embedded operating systems, Qt is supported by embedded Linux and, with the beta release of Qt 4.4, it supports Windows CE 5.0/6.0, and Windows Mobile 5.0/6.0. In this article, I create native applications for Windows CE using Qt. Windows CE targets different segments of the embedded marketplace. Windows Mobile, for instance, targets Smartphones and Pocket PCs. Windows Mobile has a specialized UI, and provides lightweight office and communication applications. Nevertheless, it’s still Windows CE. Generally speaking, when I refer to Windows CE, I include Windows Mobile and any other Windows CE flavor that supports the Windows CE Standard SDK 5.0 (or later). Qt comes with a UI builder tool for designing UIs. You can, of course, code the GUI by hand, but you can save time doing it in Qt Designer instead. Qt Designer stores the UI in an XML file, which generates C++ code that you can include in your project. Figure 2 shows the Qt Designer with the .ui file for Image Viewer. For this application, I use the QLabel, QLineEdit, and QPushButton widgets (controls). I use QLabel for the actual images and for textual information (such as the name of the current image and its dimensions). I use QLineEdit to display the name of the current directory, and QPushButton for user interactions in the application. Giving the widgets sensible names like previousImage, nextButton, and currentDirectory, it is simpler later on when using these widgets in the application code. Once you define the UI, you combine it with the application code. The generated C++ code created from the .ui file in Figure 2 results in a header file called ui_imageviewer.h. To use it, just include it in the code. Here, I subclass a QWidget and initialize the GUI in the constructor: class PreviewWindow : public QWidget { Q_OBJECT public: An Image Viewer Example To demonstrate how you can use Qt, I present an image viewer called “Qt Image Viewer” (Figure 1) and internationalize it for three different languages. It has its own custom look-and-feel—and users can change both the language and look-and-feel while the application is running. The complete source code for the application is available online; see “Resource Center,” page 5. 30 Dr. Dobb’s Journal l www.ddj.com l June 2008 http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - June 2008

Dr. Dobb's Journal - June 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries There Must Be Contest Conversations Building a Test Harness for RTOS QT and Windows CE Software to Hardware Parallelization Performance Portable C++ Effective Concurrency The Agile Edge Swaine's Flames

Dr. Dobb's Journal - June 2008

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