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C++, Qt, and Cascades

I have avoided discussing C++ until now and given you mostly a “QML/JavaScript” perspective of Cascades programming. My goal was to show you how easily you could quickly build applications using QML and JavaScript only, without even writing a single line of C++ code. By now you know enough about the Cascades programming model and it is time to look at what's happening behind the scenes in the C++ world.

QML and JavaScript provide a quick and efficient way of declaratively designing your application's UI and wiring some behavior for event handling. You will, however, reach a point where you will need to do some heavy lifting and implement core business logic in C++. The reasons for this can be manifold but they will almost certainly revolve around the following:

n Your application's business logic is complex and you don't want it scattered in QML documents.

n You need to achieve maximum performance, and JavaScript will simply not scale as well as C++ (for example, it would make no sense writing a physics engine in JavaScript).

n You need tight platform integration provided by Qt modules or BPS.

n You need to reuse third-party libraries written in C/C++.

C++ has the reputation of being a large and complex language, but the purpose of this chapter is to teach just enough so that you can efficiently build Cascades applications. I am actually going to make the bold assertion that all that you need to build Cascades applications is entirely covered in this chapter. The only prerequisite to understanding the material presented here is that you already have some OOP knowledge by having written applications in Java or Objective-C, and I will show you the equivalent C++/Qt way.

Note that the material will also strongly focus on the Qt C++ language extensions for writing applications. Cascades is heavily based on the Qt framework and therefore it is important that you have a good understanding of the underlying Qt framework. For example, I will tend to favor the Qt types, memory management, and container classes even if the standard C++ library provides equivalent functionality. (Another important reason is that the Qt containers are tightly integrated with QML and this will save us the pain of writing glue code to access standard C++ containers from QML.)

After having read this chapter, you will have a C++ perspective of Cascades programming and a good understanding of

n The Qt object model.

n Qt memory management techniques.

n The Qt container classes that you can access from QML.

n The different mechanisms for exposing C++ classes to QML.

 
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