Qt SCXML Traffic Light Example (Dynamic)

A widget-based application that uses a dynamically loaded state machine to implement a traffic light.


Traffic Light Example (Dynamic) demonstrates how to connect to the active properties of a state in a dynamically loaded state machine.

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.

Dynamically Loading the State Machine

We link against the Qt SCXML module by adding the following lines to the example’s build files.

To .pro when using qmake:

To CMakeLists.txt when using cmake:

We dynamically create the state machine in trafficlight-widgets-dynamic.cpp:

And then instantiate it:

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:

We connect to the states as follows:

Example project @ code.qt.io