Understanding the Structure of the VCD File

The structure of the VCD file has a root VoiceCommands element that contains zero or more CommandSet elements. See Listing 23.14.

The CommandSet element represents a group of commands that are activated when the value of the CommandPrefix element is spoken by the user. This allows you to group multiple phrases together.

The Example element determines the text that is displayed on the speech recognition dialog, which is displayed when the user taps and holds the phone’s Windows button.

Each CommandSet is required to have at least one Command element, and each Command element is required to have at least one and a maximum of 10 ListenFor elements. ListenFor elements define the speech that activates a particular command. Square brackets within the ListenFor element indicate that the text is optional, whereas curly braces refer to another PhraseList within the document.

In Listing 23.14 the ShowWeather command is activated when the user says any of the following phrases:

Weather for Zurich Switzerland

Weather Zurich Switzerland

Weather for London England

Weather London England

Although commands themselves cannot be added programmatically to a CommandSet at run-time, the contents of a PhraseList can be replaced programmatically. You see how to achieve this later in the chapter.

The Feedback element defines the response to the user when the command is recognized. By using curly brace notation, such as {City}, the recognized phrase list value is placed into the response.

When the voice command system recognizes a command, your app is launched and the URL specified by the Target attribute of the Navigate element is navigated to.

LISTING 23.14. VoiceCommands.xml

Click here to view code image

<?xml version="1.0" encoding="utf-8" ?>
<VoiceCommands xmlns="http://schemas.microsoft.com/voicecommands/1.0">
  <CommandSet xml:lang="en-us" Name="WeatherCommandSet">
    <CommandPrefix>Weather</CommandPrefix>
    <Example>Weather for Zurich Switzerland</Example>
    <Command Name="ShowWeather">
      <Example>Weather for Zurich Switzerland</Example>
      <ListenFor>[For] {City}</ListenFor>
      <Feedback>Showing weather for {City}</Feedback>
      <Navigate Target="Speech/VoiceCommands/VoiceCommandView.xaml"/>
    </Command>

    <PhraseList Label="City">
      <Item>Zurich Switzerland</Item>
       <Item>London England</Item>
      <!-- This phrase list is replaced programmatically
            in the VoiceCommandViewModel class. -->
    </PhraseList>
 </CommandSet>

 <!-- Other CommandSets for other languages -->

</VoiceCommands>

A wildcard token that recognizes any speech can be placed within the ListenFor element, as shown:

<ListenFor>Weather [for] {*}</ListenFor>

This allows you to define commands that register a partial match for a phrase.