SCXML 交通灯（动态、QML）

Qt Quick 应用程序使用动态加载的状态机来实现交通灯。

交通灯 QML演示了如何连接动态加载状态机中状态的活动属性。

用户界面使用Qt Quick 创建。

运行示例

要从 Qt Creator，打开Welcome 模式，从Examples 选择示例。更多信息，请参见Qt Creator: Tutorial：构建并运行。

动态加载状态机

我们通过在示例的构建文件中添加以下几行来链接Qt SCXML 模块。

使用 qmake 时添加到.pro中：

QT += qml scxml

使用 cmake 时添加到CMakeLists.txt：

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

我们在主 QML 文件中动态创建状态机：

import QtScxml
import TrafficLightApplication

Window {
    width: lights.width
    height: lights.height
    visible: true

    Lights {
        id: lights
        stateMachine: loader.stateMachine
        // Suppress qmllint warning, dynamic statemachine properties not known at compile-time
        // qmllint disable missing-property
        button.source: stateMachine.working ? "pause.png" : "play.png"
        button.onClicked: stateMachine.submitEvent(stateMachine.working ? "smash" : "repair");
        // qmllint enable missing-property
    }

    StateMachineLoader {
        id: loader
        source: Qt.resolvedUrl("statemachine.scxml")
    }
}

连接状态

在 SCXML 文件中，我们为每盏灯指定了状态：红灯、黄灯和绿灯。在<onentry> 元素中，我们指定了进入状态时要发送的事件以及发送事件前的延迟（以秒为单位）。在<transition> 元素中，我们指定了触发向target 属性指定的状态过渡的事件：

        <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>

我们连接状态的方式如下：

    states: [
        // Suppress qmllint warning, dynamic statemachine properties not known at compile-time
        // qmllint disable missing-property
        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 }
        }
        // qmllint enable missing-property
    ]

示例项目 @ code.qt.io

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