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/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\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 5.8
Item {
property QtObject 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
qmlRegisterType<MyStateMachine>("MyStateMachine", 1, 0, "MyStateMachine");
\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 a
.pro file:
\badcode
QT += scxml
STATECHARTS = MyStatemachine.scxml
\endcode
This will tell qmake to run \e qscxmlc which generates MyStatemachine.h
and MyStatemachine.cpp, and adds them to \l [QMake] HEADERS and
\l [QMake] SOURCES variables. By default, the generated files are saved in
the build directory. The \e QSCXMLC_DIR variable can be set to specify
another directory. The \e QSCXMLC_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 5.8
EventConnection {
stateMachine: stateMachine
events: ["playbackStopped"]
onOccurred: console.log("Stopped!")
}
\endqml
Sending events to a state machine is equally simple:
\code
stateMachine->submitEvent("tap", QVariantMap({
std::make_pair("artist", "Fatboy Slim"),
std::make_pair("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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