Qt SCXML 交通灯 QML 范例 (动态)

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

Traffic Light QML Example (Dynamic) demonstrates how to connect to the active properties of a state in a dynamically loaded state machine.

UI 是使用 Qt Quick 创建的。

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动态加载状态机

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

To .pro when using qmake:

QT += qml scxml

To CMakeLists.txt when using cmake:

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

We dynamically create the state machine in the main QML file:

import QtScxml
TrafficLight {
    StateMachineLoader {
        id: loader
        source: "qrc:///statemachine.scxml"
    }
    stateMachine: loader.stateMachine
}

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

范例工程 @ code.qt.io