Qt SCXML 媒体播放器范例 (静态)

A widget-based application that sends data to and receives it from a compiled ECMAScript data model.

Media Player Example (Static) demonstrates how to access data from an ECMAScript data model that is compiled into a C++ class.

UI 是使用 Qt Widgets 创建的。

运行范例

要运行范例从 Qt Creator ，打开欢迎模式，然后选择范例从范例。更多信息，拜访构建和运行范例 .

使用 ECMAScript 数据模型

We specify the data model as a value of the datamodel 属性在 <scxml> element in mediaplayer-common/mediaplayer.scxml :

<scxml
    xmlns="http://www.w3.org/2005/07/scxml"
    version="1.0"
    name="MediaPlayerStateMachine"
    initial="stopped"
    datamodel="ecmascript"
>
    <datamodel>
        <data id="media"/>
    </datamodel>

编译状态机

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

QT += widgets scxml

接着，指定要编译的状态机：

STATECHARTS = ../mediaplayer-common/mediaplayer.scxml

Qt SCXML 编译器 qscxmlc , is run automatically to generate statemachine.h and statemachine.cpp , and to add them to the HEADERS and SOURCES variables for compilation.

实例化状态机

We instantiate the generated MediaPlayerStateMachine class in mediaplayer-widgets-static.cpp :

#include "mediaplayer.h"
#include "../mediaplayer-common/mainwindow.h"
#include <QApplication>
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    MediaPlayerStateMachine machine;
    MainWindow mainWindow(&machine);

连接到状态

The media player state machine will send out events when users tap a control and when playback starts or stops, as specified in the SCXML file:

    <state id="stopped">
        <transition event="tap" cond="isValidMedia()" target="playing"/>
    </state>
    <state id="playing">
        <onentry>
            <assign location="media" expr="_event.data.media"/>
            <send event="playbackStarted">
                <param name="media" expr="media"/>
            </send>
        </onentry>
        <onexit>
            <send event="playbackStopped">
                <param name="media" expr="media"/>
            </send>
        </onexit>
        <transition event="tap" cond="!isValidMedia() || media === _event.data.media" target="stopped"/>
        <transition event="tap" cond="isValidMedia() && media !== _event.data.media" target="playing"/>
    </state>

To be notified when a state machine sends out an event, we connect to the corresponding signals:

    stateMachine->connectToEvent("playbackStarted", this, &MainWindow::started);
    stateMachine->connectToEvent("playbackStopped", this, &MainWindow::stopped);

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