SCXML 交通灯（动态，小部件）

这是一个基于 Widget 的应用程序，它使用动态加载的状态机来实现交通灯。

交通灯演示了如何在动态加载的状态机中连接状态的活动属性。

用户界面使用Qt Widgets 创建。

运行示例

运行示例 Qt Creator，打开Welcome 模式，并从Examples 中选择示例。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 += widgets scxml

使用 cmake 时添加到CMakeLists.txt：

find_package(Qt6 REQUIRED COMPONENTS Core Gui Scxml Widgets)

target_link_libraries(trafficlight-widgets-dynamic PRIVATE
    Qt6::Core
    Qt6::Gui
    Qt6::Scxml
    Qt6::Widgets
)

我们在trafficlight-widgets-dynamic.cpp 中动态创建状态机：

#include "../trafficlight-common/trafficlight.h"

#include <QtWidgets/qapplication.h>
#include <QtCore/qiodevice.h>
#include <QtCore/qtextstream.h>

using namespace Qt::Literals::StringLiterals;

int main(int argc, char **argv)
{
    QApplication app(argc, argv);

    QScxmlStateMachine *machine = QScxmlStateMachine::fromFile(u":statemachine.scxml"_s);

    if (!machine->parseErrors().isEmpty()) {
        QTextStream errs(stderr, QIODevice::WriteOnly);
        const auto errors = machine->parseErrors();
        for (const QScxmlError &error : errors) {
            errs << error.toString();
        }
        return -1;
    }

然后将其实例化：

    TrafficLight widget(machine);
    widget.show();
    machine->setParent(&widget);
    machine->start();

    return app.exec();
}

连接状态

在 SCXML 文件中，我们为每个灯指定了状态：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：

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

示例项目 @ code.qt.io

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