Qt SCXML Invoke Example (Dynamic)

Invoke Example (Dynamic) demonstrates how to use the <invoke> element with generated nested state-machines, where the SCXML file is dynamically loaded. The <invoke> element is used to create an instance of an external service.

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.

Invoking the State Machine

In statemachine.scxml, we specify a state machine with the name Directions of type http://www.w3.org/TR/scxml/ to invoke:

 <scxml
     xmlns="http://www.w3.org/2005/07/scxml"
     version="1.0"
     name="Directions"
     initial="anyplace"
 >
     <state id="anyplace">
         <transition event="goNowhere" target="nowhere"/>
         <transition event="goSomewhere" target="somewhere"/>

         <state id="nowhere"/>
         <state id="somewhere">
             <invoke type="http://www.w3.org/TR/scxml/">
                 <content>
                     <scxml name="anywhere" version="1.0">
                         <state id="here">
                             <transition event="goThere" target="there"/>
                         </state>
                         <state id="there">
                             <transition event="goHere" target="here"/>
                         </state>
                     </scxml>
                 </content>
             </invoke>
         </state>
     </state>
 </scxml>

Dynamically Loading the State Machine

We link against the Qt SCXML module by adding the following line to the project build files.

With qmake to the invoke-dynamic.pro

 QT += qml scxml

With cmake to the CMakeLists.txt

 find_package(Qt6 COMPONENTS Core Gui Qml Scxml)

 target_link_libraries(invoke-dynamic PUBLIC
     Qt6::Core
     Qt6::Gui
     Qt6::Qml
     Qt6::Scxml
 )

We dynamically create the state machine, as follows:

 import QtScxml

 MainView {
     stateMachine: directions.stateMachine

     StateMachineLoader {
         id: directions
         source: "qrc:///statemachine.scxml"
     }

Example project @ code.qt.io