Qt 4 raises the bar for cross-platform application development tools

Trolltech's comprehensive toolkit simplifies code portability, interoperability

Cross-platform toolkits have always been a market unto themselves. In the heyday of Unix, products such as Galaxy, XVT, and Zinc provided a solution for IT and for ISVs that could not afford to rewrite code for all flavors of OSes. When Java took over much of the cross-platform workload, these tools were relegated to the sidelines.

But, as years passed, it became evident that Java was not ideally suited to developing client-facing applications, and a new generation of GUI toolkits arose with strong open source roots.

One of those toolkits, Trolltech’s Qt, has evolved into a far more comprehensive library that provides robust support in such disparate areas as database access, XML processing, threading, network programming, and advanced data structures.

Backed by a commercial venture that offers a commercial license, Qt comes in three versions: the new Console Edition, a server-oriented package that bundles the non-GUI classes with a text-based front end; Desktop Light Edition, primarily the GUI toolkit; and Desktop Edition, which combines the two versions -- server back end with GUI front end -- and provides the most comprehensive libraries.

I looked at the Desktop Edition of the new Qt 4 release, and I found that improved graphics and multithreading support, as well as integration in Visual Studio .Net, make this toolkit significantly better.

The GUI Bits

Qt’s GUI toolkit is unique in that it uses the underlying operating system’s widget set to provide the interface. As a result, applications have a native look and feel. The set of widgets is remarkably complete. Beyond the standard controls, the library has toolbars, tool tips, grids into which images and rich text can be placed, drag-and-drop support, floating menu bars, and more.

A bundled visual design tool, Qt Designer, enables interactive GUI design. Qt Designer generates an XML metafile from which a utility generates the necessary C++ source code. To the widget set, Qt adds a complete, high-end rendering system including sophisticated drawing functions, OpenGL graphics, rich text, and imaging.

The rich text capabilities are particularly impressive: Qt automatically accesses the fonts available on the execution platform. Fonts can be chosen by name and characteristics; if the specified font is unavailable, Qt intelligently finds the closest matching typeface and size. You can combine letters from many fonts to provide true rich text.

The system also supports Unicode fonts, so all forms of foreign characters work correctly. Text can be wrapped around embedded graphics, and other rarely found text-rendering capabilities are built in, including 2-D and 3-D graphics, animation, and interchangeable paint engines (OpenGL, PostScript, and so on).

The non-GUI portions of Qt 4 handle some of portability’s most irritating details, the worst of which are parallel processing and the use of threads. Qt’s library abstracts the underlying threads’ resources and gives them a sane organization that borrows conceptually from both Windows threads and Pthreads.

Qt 4 also abstracts sockets, greatly simplifying network programming. It provides plenary support for HTTP, FTP, TCP, and UDP (User Datagram Protocol), and if you use your own protocol, Qt will support that, too.

Because different platforms might rely on differing implementations of standard templates, Qt provides an entirely portable set of data structures, including all the usual containers, as well as sophisticated items such as LRU (least recently used) caches. The product also has classes for database access (via embedded SQL) and for XML processing, with support for DOM and SAX2. A bundled XML parser can be used if other access is necessary.

Feeling Your Way

Using any app dev toolkit requires a commitment. You must understand how the library is laid out and its fundamental design, and then learn how to make use of it. Qt makes this process straightforward with extensive documentation, including numerous detailed examples. If you get into a jam, you can tap the large Qt user community. This community grew up around Qt because the toolkit is the basis of KDE, one of the two major UIs for desktop Linux. Hence, there is a lot of public domain code that uses Qt.

Unlike the APIs used in OSes (Win32 or POSIX), Qt did not grow organically. Rather, developers who made sure that calling conventions and syntax stayed uniform tended it, so Qt is far easier to use than most other large API sets. After a few weeks of using Qt, it becomes easy to guess the names of APIs you need when entering into a new programming domain.

The commercial Qt 4 product (but not the open source version) includes a new integration utility for Visual Studio .Net users. It plugs Qt Designer into the Microsoft IDE, loads Qt documentation into the Visual Studio help system, provides code completion, and bundles Visual Studio .Net templates for Qt projects. This is a useful feature that lets you design, code, and test Qt apps without leaving the environment.

The library’s largest failing, in my opinion, is that it works only with C++ . However, rather than force developers to know recondite aspects of the language, the Qt APIs and functions require only basic knowledge of C++. Any C or Java programmer will quickly figure out how to use the library.

Cross-Platform Quality

After years of testing cross-platform toolkits, I can say that none approach Qt’s breadth of functionality or quality of implementation. I recommend Qt even for single-platform projects, as Qt is easier to learn than most OS API sets; it is much better designed, and its interfaces change less frequently. The easy portability is an added bonus.

My only reservations about Qt 4 are minor: The lack of bindings other than C++ is a bit of a handicap (Trolltech is working on this issue for future versions). Also, the highest level of tech support provides only e-mail responses to inquiries. My tests show that answers arrive within 24 hours, and I can set up a phone conference by special arrangement, but there is no standard phone offering.

These are trivial complaints; Qt users have known for a long time that they enjoy an excellent library at a terrific price. With Qt 4, an already great product makes another leap forward.

InfoWorld Scorecard
Portability (25.0%)
Documentation (10.0%)
Value (10.0%)
Capability (30.0%)
Ease of use (25.0%)
Overall Score (100%)
Trolltech Qt 4 9.0 8.0 9.0 10.0 9.0 9.2
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