Qt SCXML 媒體播放器範例 (靜態)

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 創建的。

運行範例

要運行範例從 Qt Creator ，打開歡迎模式，然後選擇範例從範例。更多信息，拜訪構建和運行範例 .

使用 ECMAScript 數據模型

We specify the data model as a value of the datamodel 屬性在 <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>

編譯狀態機

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

QT += widgets scxml

接著，指定要編譯的狀態機：

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

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

實例化狀態機

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);

連接到狀態

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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