SCXML Traffic Light (Static, QML)

A Qt Quick application that uses a compiled state machine to implement a traffic light.

Traffic Light demonstrates how to connect to the active properties of a state in a state machine that is compiled to a class.

UI 是使用 Qt Quick 创建的。

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编译状态机

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

.pro when using qmake:

QT += qml scxml

接着，指定要编译的状态机：

STATECHARTS = ../trafficlight-common/statemachine.scxml

CMakeLists.txt when using cmake:

find_package(Qt6 REQUIRED COMPONENTS Core Gui Qml Scxml)
target_link_libraries(trafficlight-qml-static PRIVATE
    Qt6::Core
    Qt6::Gui
    Qt6::Qml
    Qt6::Scxml
)

接着，指定要编译的状态机：

qt6_add_statecharts(trafficlight-qml-static
    ../trafficlight-common/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.

实例化状态机

We instantiate the state machine as follows:

import TrafficLightApplication
Window {
    width: lights.width
    height: lights.height
    visible: true
    Lights {
        id: lights
        stateMachine: TrafficLightStateMachine {
            running: true
        }

连接到状态

In the SCXML file, we specify states for each light: red, yellow, and green. In the <onentry> element, we specify the event to send when entering the state and the delay in seconds before sending the event. In the <transition> element, we specify the event that triggers the transition to the state specified by the target 属性：

        <state id="red">
            <onentry>
                <send event="startGoingGreen" delay="3s"/>
            </onentry>
            <transition event="startGoingGreen" target="redGoingGreen"/>
        </state>
        <state id="yellow" initial="greenGoingRed">
            <state id="redGoingGreen">
                <onentry>
                    <send event="goGreen" delay="1s"/>
                </onentry>
                <transition event="goGreen" target="green"/>
            </state>
            <state id="greenGoingRed">
                <onentry>
                    <send event="goRed" delay="1s"/>
                </onentry>
                <transition event="goRed" target="red"/>
            </state>
        </state>
        <state id="green">
            <onentry>
                <send event="startGoingRed" delay="3s"/>
            </onentry>
            <transition event="startGoingRed" target="greenGoingRed"/>
        </state>

We connect to the states as follows:

    states: [
        State {
            name: "Red"
            when: lights.stateMachine.red
            PropertyChanges { redLight.opacity: 1 }
        },
        State {
            name: "RedGoingGreen"
            when: lights.stateMachine.redGoingGreen
            PropertyChanges { redLight.opacity: 1 }
            PropertyChanges { yellowLight.opacity: 1 }
        },
        State {
            name: "Yellow"
            when: lights.stateMachine.yellow || lights.stateMachine.blinking
            PropertyChanges { yellowLight.opacity: 1 }
        },
        State {
            name: "Green"
            when: lights.stateMachine.green
            PropertyChanges { greenLight.opacity: 1 }
        }
    ]

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