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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page qtscxml-instantiating-state-machines.html
\title Instantiating State Machines
\brief Instantiating dynamically created and compiled state machines in C++
and QML
Both the dynamically created and the compiled state machines behave in the
same way, have the same properties, states, data model, and so on. They only
differ in the way they are instantiated. To dynamically create one in C++
from an SCXML file, you can use:
\code
auto *stateMachine = QScxmlStateMachine::fromFile("MyStatemachine.scxml");
\endcode
Or, in QML:
\qml
import QtScxml
Item {
property StateMachine stateMachine: scxmlLoader.stateMachine
StateMachineLoader {
id: scxmlLoader
source: "statemachine.scxml"
}
}
\endqml
A compiled state machine can be instantiated the same way as any C++
object:
\code
auto *stateMachine = new MyStatemachine;
\endcode
Or:
\code
MyStatemachine stateMachine;
\endcode
To use a compiled state machine in QML, you can register it as a QML type:
\code
struct MyStateMachineRegistration {
Q_GADGET
QML_NAMED_ELEMENT(MyStateMachine)
QML_FOREIGN(MyStateMachine)
QML_ADDED_IN_VERSION(1, 0)
};
\endcode
Then you can instantiate it in QML, like this:
\qml
import MyStateMachine 1.0
MyStateMachine {
id: stateMachine
}
\endqml
To compile a state machine, the following lines have to be added to the
project build file:
When using cmake:
\include qtscxml-module-use.qdocinc cmakebuild
\include qtscxml-module-use.qdocinc cmakestatecharts
When using qmake:
\include qtscxml-module-use.qdocinc qmakebuild
\include qtscxml-module-use.qdocinc qmakestatecharts
This will tell qmake to run \e qscxmlc which generates MyStatemachine.h
and MyStatemachine.cpp, and adds them to appropriately to the project
headers and sources. By default, the generated files are saved in
the build directory. The qmake \e QSCXMLC_DIR or cmake \e OUTPUT_DIRECTORY
variable can be set to specify another directory. The qmake
\e QSCXMLC_NAMESPACE or cmake \e NAMESPACE variable can be set to put the
state machine code into a C++ namespace.
After instantiating a state machine, you can connect to any state's
active property as follows. For example, if the state machine for a
traffic light has a state indicating that the light is red (which has the
convenient id "red" in the scxml file), you can write:
\code
stateMachine->connectToState("red", [](bool active) {
qDebug() << (active ? "entered" : "exited") << "the red state";
\endcode
And in QML:
\qml
Light {
id: greenLight
color: "green"
visible: stateMachine.green
}
\endqml
If you want to be notified when a state machine sends out an event, you
can connect to the corresponding signal. For example, for a media player
state machine which indicates that playback has stopped by sending an
event, you can write:
\code
stateMachine->connectToEvent("playbackStopped", [](const QScxmlEvent &){
qDebug() << "Stopped!";
});
\endcode
And in QML:
\qml
import QtScxml
EventConnection {
stateMachine: stateMachine
events: ["playbackStopped"]
onOccurred: console.log("Stopped!")
}
\endqml
Sending events to a state machine is equally simple:
\code
stateMachine->submitEvent("tap", QVariantMap({
{ "artist", "Fatboy Slim" },
{ "title", "The Rockafeller Skank" }
});
\endcode
This will generate a "tap" event with the map contents available in
_event.data inside the state machine. In QML:
\code
stateMachine.submitEvent("tap", {
"artist": "Fatboy Slim"
"title": "The Rockafeller Skank"
})
\endcode
\note A state machine needs a \c QEventLoop to work correctly. The event loop is used
to implement the \c delay attribute for events and to schedule the processing of a state machine
when events are received from nested (or parent) state machines. A QML application or a widget
application will always have an event loop running, so nothing extra is needed. For other
applications, \c QApplication::run will have to be called to start the event loop processing.
*/
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