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Chapter 8. openETCS Domain Framework
Figure 8.5.: Class diagram of the DMI classes
able to inform any observer about a changed subject. On the other hand, each observer only
holds a pointer to one CEVCStateMachine object that it observes. Via this m_pStateMachine
aggregation, an observer can access the currently active CDMISubject object to read data from
the EVC to the driver or set data entered in the observer by the driver.
CDMIQWidget is a concrete observer implementation using the Qt 4 [59] framework. Qt 4
was chosen because it provides platform independent GUI development in the C++ programming
language [79], which means in an object-oriented manner. This is required by Req.6 and Req.7.
The concrete elements 6 for inputs and outputs are generated dynamically since those typically
vary for different ETCS Modes or rather CEVCState instances. The input and output elements
are stored in the m_OutputWidgets and m_InputWidgets compositions. For those, a pointer
to the QWidget [59] class is used as data type. A QWidget is the very basic type of all classes
in Qt 4 representing graphical elements. Which concrete, derived classes are used, depends on
the CDMIInput and CDMIOuput objects in the current CDMISubject. Since this is of low
relevance, those certain types will be not discussed here. The CDMIQWidget observer class
itself is also a QWidget, which mainly has the advantage that it can be used as standalone
dialogue but also can be integrated or combined with other Qt 4 elements if required. The
inputs and outputs of the subject are aligned in a grid respectively in two columns: Outputs
on the left side, inputs on the right side. The corresponding graphical arrangement is provided
by the m_Layout composition to the QGridLayout [59] class. For the graphical definition of the
meaning of each input or output element in CDMIQWidget, labels are used, which are located
on the left side of each graphical element. Those correspond to the m_Labels composition to
6 widgets in terms of Qt
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