Qt SCXML 交通灯范例 (动态)

A widget-based application that uses a dynamically loaded state machine to implement a traffic light.

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

UI 是使用 Qt Widgets 创建的。

运行范例

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动态加载状态机

We link against the Qt SCXML module by adding the following line to the example .pro 文件：

QT += widgets scxml
					

We dynamically create the state machine in trafficlight-widgets-dynamic.cpp :

#include "../trafficlight-common/trafficlight.h"
#include <QApplication>
#include <QTextStream>
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QScxmlStateMachine *machine = QScxmlStateMachine::fromFile(
                QStringLiteral(":statemachine.scxml"));
    if (!machine->parseErrors().isEmpty()) {
        QTextStream errs(stderr, QIODevice::WriteOnly);
        const auto errors = machine->parseErrors();
        for (const QScxmlError &error : errors) {
            errs << error.toString();
        }
        return -1;
    }
					

And then instantiate it:

    TrafficLight widget(machine);
    widget.show();
    machine->setParent(&widget);
    machine->start();
    return app.exec();
}
					
					

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:

    machine->connectToState(QStringLiteral("red"),
                            widget->redLight(), &LightWidget::switchLight);
    machine->connectToState(QStringLiteral("redGoingGreen"),
                            widget->redLight(), &LightWidget::switchLight);
    machine->connectToState(QStringLiteral("yellow"),
                            widget->yellowLight(), &LightWidget::switchLight);
    machine->connectToState(QStringLiteral("blinking"),
                            widget->yellowLight(), &LightWidget::switchLight);
    machine->connectToState(QStringLiteral("green"),
                            widget->greenLight(), &LightWidget::switchLight);
					

范例工程 @ code.qt.io

内容

• 运行范例

• 动态加载状态机

• 连接到状态