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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example pingpong
\title Ping Pong States
\ingroup examples-qtstatemachine
\brief The Ping Pong States example shows how to use parallel states together
with custom events and transitions in \l{Qt State Machine Overview}{Qt State Machine Framework}.
This example implements a statechart where two states communicate by
posting events to the state machine. The state chart looks as follows:
\image pingpong-example.png
The \c pinger and \c ponger states are parallel states, i.e. they are
entered simultaneously and will take transitions independently of
each other.
The \c pinger state will post the first \c ping event upon entry; the \c
ponger state will respond by posting a \c pong event; this will cause the
\c pinger state to post a new \c ping event; and so on.
\snippet pingpong/main.cpp 0
Two custom events are defined, \c PingEvent and \c PongEvent.
\snippet pingpong/main.cpp 1
The \c Pinger class defines a state that posts a \c PingEvent to the state
machine when the state is entered.
\snippet pingpong/main.cpp 2
The \c PingTransition class defines a transition that is triggered by
events of type \c PingEvent, and that posts a \c PongEvent (with a delay
of 500 milliseconds) to the state machine when the transition is
triggered.
\snippet pingpong/main.cpp 3
The \c PongTransition class defines a transition that is triggered by
events of type \c PongEvent, and that posts a \c PingEvent (with a delay
of 500 milliseconds) to the state machine when the transition is
triggered.
\snippet pingpong/main.cpp 4
The main() function begins by creating a state machine and a parallel
state group.
\snippet pingpong/main.cpp 5
Next, the \c pinger and \c ponger states are created, with the parallel
state group as their parent state. Note that the transitions are \e
targetless. When such a transition is triggered, the source state won't be
exited and re-entered; only the transition's onTransition() function will
be called, and the state machine's configuration will remain the same,
which is precisely what we want in this case.
\snippet pingpong/main.cpp 6
Finally, the group is added to the state machine, the machine is started,
and the application event loop is entered.
*/
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