SCXML Invoke | Qt SCXML | Qt 6.11.0
Description: Invokes a compiled nested state machine.

- Qt 6.11
- Qt SCXML
- Qt SCXML Examples
- SCXML Invoke
- Qt 6.11.0 Reference Documentation

# SCXML Invoke

Invokes a compiled nested state machine.

Invoke demonstrates how to use the `<invoke>` element with generated nested state-machines, where the SCXML file is compiled to a C++ class. 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, see Qt Creator: Tutorial: Build and run.

#### Invoking the State Machine

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

     <scxml
         xmlns="http://www.w3.org/2005/07/scxml"
         version="1.0"
         name="DirectionsStateMachine"
         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>

#### Compiling the State Machine

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

##### invoke.pro when using qmake:

     QT += qml scxml

We then specify the state machine to compile:

     STATECHARTS = statemachine.scxml

##### CMakeLists.txt when using cmake:

     find_package(Qt6 REQUIRED COMPONENTS Core Gui Qml Scxml)

     target_link_libraries(invoke PRIVATE
         Qt6::Core
         Qt6::Gui
         Qt6::Qml
         Qt6::Scxml
     )

We then specify the state machine to compile:

     qt6_add_statecharts(invoke
         statemachine.scxml
     )

The statechart directives STATECHARTS or qt6_add_statecharts invoke the Qt SCXML Compiler, `qscxmlc`, which is run automatically to generate statemachine.h and statemachine.cpp, which are then added appropriately as headers and sources for compilation.

#### Declaring the state machine as QML element

The state machine is declared as a QML element as follows:

     struct DirectionsStateMachineRegistration
     {
         Q_GADGET
         QML_FOREIGN(DirectionsStateMachine)
         QML_NAMED_ELEMENT(DirectionsStateMachine)
         QML_ADDED_IN_VERSION(1, 0)
     };

#### Instantiating the State Machine

We instantiate the generated `DirectionsStateMachine` element in the MainView.qml file, as follows:

         DirectionsStateMachine {
             id: stateMachine
             running: true
         }

Example project @ code.qt.io