Audio List Markup

Node Class References: Audio, LabelList

For some applications that use an Audio node, a user interface to allow selection from a set of audio items, and visual indicators of the currently-selected audio item, is required.

For these applications, the ContentNode node that is assigned to the Audio node content field can contain as many Content Meta-Data descriptive attributes as needed to meet the user interface requirements of the application.

For this Audio node example, we'll just allow a user to select an audio item from a LabelList node list. We could use any of the list and grid nodes described in Creating Lists and Grids, but for this example we'll use a simple list. We also could set up a more elaborate user interface, that would show more descriptive text and images for each audio item as the user scrolls down the list. For example, we could show information about each song in a list of songs, such as the length, musicians, songwriters, and so forth. For ideas on how to implement that type of interface, see Video List Markup below.

But we will add some additional control functions for the audio playback compared to the very simple AudioExample to allow users to stop an audio item during playback, and reset the Audio node after an audio item has completed playback. From audiolistscene.xml in AudioListExample.zip, note the playaudio() and controlaudio() callback functions, triggered by the LabelList node itemselected and Audio node state fields respectively:

sub init() 
  ...
  m.audiolist.observeField("itemSelected", "playaudio")
  ...
  m.audio.observeField("state", "controlaudioplay")
  ...
end sub
...

sub playaudio()
  m.audio.control = "stop"
  m.audio.control = "none"
  m.audio.control = "play"
end sub

sub controlaudioplay()
  if (m.audio.state = "finished")
    m.audio.control = "stop"
    m.audio.control = "none"
  end if
end sub

Remember Observed Fields Markup? So when the user selects the audio item from the list, the playaudio() function is called. When the audio item has a playback state change, the controlaudioplay() function is called to reset the Audio node if the playback has completed. And we'll need a remote key event handler if the user presses the Back key to stop an audio item playback (review Key Events Markup if needed):

function onKeyEvent(key as String,press as Boolean) as Boolean
  if press then
    if key = "back"
      if (m.audio.state = "playing")
        m.audio.control = "stop"
        return true
      end if
    end if
  end if
  return false
end function

The remainder of the audiolistscene.xml file is the element, containing the XML Group node layout of the scene visual elements: the LabelList and Poster nodes.

You can see how the content meta-data for the LabelList node is used to set the audio item strings in the list using the Content Meta-Data title attribute, as well as setting the streamFormat and Url Content Meta-Data attributes for audio playback:

http://www.sdktestinglab.com/Tutorial/content/audiocontent.xml

<Content >
  <item 
    title = "Main Menu" 
    streamformat = "mp3" 
    url = "http://www.sdktestinglab.com/Tutorial/sounds/mainmenu.mp3" />
  ...