Qt SCXML Media Player Example (Dynamic) | Qt SCXML 5.9

Qt 5.9 | Qt SCXML | Qt SCXML Examples | Qt SCXML Media Player Example (Dynamic)

Qt 5.9.3 Reference Documentation

# Qt SCXML Media Player Example (Dynamic)

Media Player Example (Dynamic) demonstrates how to access data from a dynamically loaded ECMAScript data model.

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>

## Dynamically Loading the State Machine

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

      QT += widgets scxml

We dynamically create and instantiate the state machine in mediaplayer-wigdets-dynamic/mediaplayer-widgets-dynamic.cpp:

      #include "../mediaplayer-common/mainwindow.h"

      #include <QScxmlStateMachine>
      #include <QApplication>

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

          auto machine = QScxmlStateMachine::fromFile(QStringLiteral(":mediaplayer.scxml"));
          MainWindow mainWindow(machine);
          machine->setParent(&mainWindow);

          machine->start();
          mainWindow.show();
          return app.exec();
      }

## 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);

Files:

- mediaplayer-widgets-dynamic/mediaplayer-widgets-dynamic.cpp
- mediaplayer-widgets-dynamic/mediaplayer-widgets-dynamic.pro
- mediaplayer-widgets-dynamic/mediaplayer.qrc