Qt Framework

The Qt framework is a cross-platform application framework that is extensively used for creating applications that are executable on different software and hardware platforms without any alteration or fairly simple diminutive changes required in the underlying codebase. This ability to develop cross-platform software from a particular framework is one of the major strengths of Qt. It can be used as a platform for creating embedded systems, application software that requires GUI (Graphical User Interface) controls, software that runs as processes on operating systems, command line tools, server apps, libraries, mobile apps etc.

Qt runs on several mobile platforms and popular desktop operating system platforms such as Linux, Windows and Mac OS X. It provides features for database access (sql), thread management, network support, JSON and XML parsing. It has a remarkable collection of modules which includes:

• QtCore which is a base library that offers containers, thread management, event management etc.
• QtGui and QtWidgets which is a GUI toolkit for desktop apps. It provides graphical components required to design applications.
• QtWebkit is the webkit solution that facilitates the use of web pages and web apps in a Qt application.
• QtSQL is the SQL relational database management abstraction layer extensible with drivers and provides support for ODBC, MySQL , SQLITE and PostgreSQL data sources.
• QtNetwork which offers a handy collection of classes useful for network programming.
• QtXML which offers support for simple XML parsing (SAX) and DOM and QtXmlPatterns, which provides support for XSLT, XPath, XQuery and Schema validation

Developers would be interested to know that Qt’s SDK can be downloaded and deployed by downloading an installer or built from source.

Functionality and Ease of Use.

The latest version of the framework has enhanced graphics quality (this is possible with the use of OpenGL ES, the version of the graphics application programming interface designed specifically for embedded systems and mobile devices), support for C++11, HTML5 support with QtWebKit 2 and a vastly upgraded QML engine with new APIs. The Qt WebKit integrated browser engine permits integration of web content and apps. So the prospective HTML5 developer can expect  to develop hybrid applications that blend the responsiveness and power of native code with huge quantities of dynamic content. The Qt framework is based on C++ and experienced programmers can easily hit the ground running especially if they familiar with abstract concepts like memory management  I/O devices, stacks etc. Newbies might be expected to struggle for a while before they can fully harness the power of this tool and this implies that they may experience a longer learning curve.

Documentation and Support.

There is an extensive set of documentation available for Qt.  This includes help files, wikis, code samples, API documentation, developer guides, online forums, communities (for newbies, intermediate and experienced users) and video tutorials.  You also have broad Qt reference pages, framework manuals, tools porting & platforms reference and documentation archives for developers. When you have a license subscription for commercially licensed Qt versions (for application development) you are entitled to receive technical support and updates from the Qt support team. This might be through direct contact or logging support issues through your Qt account. The vendor provides a system called Qt Bugtracker where developers can log bug reports for Qt Installer Framework project or review known issues. Some developers have suggested that the documentation from the vendor can be better improved especially for highly technical concepts and features.

Licensing

Qt is available with both commercial and open source GPL 2.0, GPL 3.0, and LGPL 3.0 licenses depending on the Qt module and version. A free trial commercial version of the solution is available online and users can download and use the commercial version of the solution for thirty days as specified on the vendor’s portal. The general Qt toolkit, which consists of Qt essential code libraries, the Qt add-on APIs, and the Qt creator IDE are all available  for commercial and GPL licenses. The majority of the Qt APIs are also available under LGPLv3 license but not all of the Qt add-on modules are included.

Some important notes about the licensing.

• Each developer must have his or her own singly allotted Qt license (Licenses are per individual). The vendor clearly states that it does not permit users or organizations to combine Qt commercial licenses with Qt LGPL licenses in one project.
• Currently, users can download and try out the commercial version of the framework for free for a thirty day period. During that time, you can develop applications with Qt, but you are not permitted to distribute your applications before you purchase a paid license. After the free 30-day trial period, you will to need to acquire a license to continue using the software.
• Users who purchase the commercial license can pay for a term subscription or perpetual license.
• Users who are interested in the commercial version of Qt have the option of buying the online version which is offered as a term license subscription. The development license is valid only when there is an active subscription. The perpetual license which is persistently valid can be renewed on an annual basis so as to enjoy support and updates to Qt's solutions.
• All the commercially licensed Qt versions allow for modification of libraries for application development and the vendor recommends that developers building and deploying applications for desktop or mobile platforms should acquire a license termed “Qt for Application Development”. This license can be purchased directly from Qt Sales or through the online portal through a monthly subscription model. Developers building and deploying devices are advised to procure a license termed “Qt for Device Creation”.
• For developers in the mobile space, you should know that Qt’s open source licenses are not compatible with distribution on most app stores. You will more likely than not need a commercial license to ship apps to an app store.

Conclusion

Qt’s framework is a potent cross-platform application framework that provides effective features for  desktop, embedded systems and mobile developers to  develop robust, interactive and platform-independent apps. The most recent version of the framework has a new modularized code base, consisting of essentials and add-on modules, which enables the system code size to be more compact and portable.