Qt SCXML Traffic Light Example (Static)▲
Traffic Light Example (Static) demonstrates how to connect to the active properties of a state in a state machine that is compiled to a class.
The UI is created using Qt Widgets.
Running the Example▲
To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.
Compiling the State Machine▲
We link against the Qt SCXML module by adding the following line to the .pro file:
QT +=
qml scxml
We then specify the state machine to compile:
STATECHARTS =
../
trafficlight-
common/
statemachine.scxml
The Qt SCXML Compiler, qscxmlc, is run automatically to generate statemachine.h and statemachine.cpp, and to add them to the HEADERS and SOURCES variables for compilation.
Instantiating the State Machine▲
We instantiate the generated TrafficLightStateMachine class in the trafficlight-widgets-static.cpp file, as follows:
#include
"statemachine.h"
#include
"../trafficlight-common/trafficlight.h"
#include <QApplication>
int
main(int
argc, char
**
argv)
{
QApplication app(argc, argv);
TrafficLightStateMachine machine;
TrafficLight widget(&
amp;machine);
widget.show();
machine.start();
return
app.exec();
}
Connecting to States▲
In the SCXML file, we specify states for each light: red, yellow, and green. In the <onentry> element, we specify the event to send when entering the state and the delay in seconds before sending the event. In the <transition> element, we specify the event that triggers the transition to the state specified by the target attribute:
&
lt;state id=
"red"
&
gt;
&
lt;onentry&
gt;
&
lt;send event=
"startGoingGreen"
delay=
"3s"
/&
gt;
&
lt;/
onentry&
gt;
&
lt;transition event=
"startGoingGreen"
target=
"redGoingGreen"
/&
gt;
&
lt;/
state&
gt;
&
lt;state id=
"yellow"
initial=
"greenGoingRed"
&
gt;
&
lt;state id=
"redGoingGreen"
&
gt;
&
lt;onentry&
gt;
&
lt;send event=
"goGreen"
delay=
"1s"
/&
gt;
&
lt;/
onentry&
gt;
&
lt;transition event=
"goGreen"
target=
"green"
/&
gt;
&
lt;/
state&
gt;
&
lt;state id=
"greenGoingRed"
&
gt;
&am