- Qt 5.15
- Qt SCXML
- Qt SCXML Examples
- Qt SCXML Media Player Example (Static)
- Qt 5.15.18 Reference Documentation

# Qt SCXML Media Player Example (Static)

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.

The UI is created using Qt Widgets.

#### Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

#### Using the ECMAScript Data Model

We specify the data model as a value of the datamodel attribute of the `<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>

#### Compiling the State Machine

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

     QT += widgets scxml

We then specify the state machine to compile:

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

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

#### Instantiating the State Machine

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);

#### Connecting to States

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() &amp;&amp; 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);

Example project @ code.qt.io