Qt SCXML 交通灯 QML 范例 (简单)

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

Traffic Light QML Example (Simple) 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 COMPONENTS Core Gui Qml Scxml)
target_link_libraries(trafficlight-qml-static PUBLIC
    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:

    TrafficLightStateMachine {
        id: stateMachine
        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 attribute:

        <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:

        Light {
            anchors.top: parent.top
            anchors.horizontalCenter: parent.horizontalCenter
            color: "red"
            visible: stateMachine.red || stateMachine.redGoingGreen
        }
        Light {
            anchors.centerIn: parent
            color: "yellow"
            visible: stateMachine.yellow || stateMachine.blinking
        }
        Light {
            anchors.bottom: parent.bottom
            anchors.horizontalCenter: parent.horizontalCenter
            color: "green"
            visible: stateMachine.green
        }
    }
							

范例工程 @ code.qt.io