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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
++ \examplecategory {Data Processing & I/O}
++
++ \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
++ {Two parallel states: pinger posts ping on entry and responds to pong,
++ ponger responds to ping by posting pong}
++
++ 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.
++
++ */