Handling Events
Invalid Input
Handling forms requires more than simply gathering field input. If
the user provides input that doesn't match the grammar, Tellme will look for
the nomatch element. If it doesn't exist, the application
will croak. The most common way to handle invalid input is to tell the user so
and ask them for the information again.
<?xml version="1.0"?>
<vxml version="1.0" >
<form id="hello">
<field name="pin">
<grammar>
<![CDATA[
Four_digits
]]>
</grammar>
<prompt>Please enter your 4 digit pin code.</prompt>
<filled>
<submit next="http://www.webreference.com/cgi-bin/perl/20/pin.pl"/>
</filled>
<nomatch>Invalid pin code.
<reprompt/>
</nomatch>
</field>
</form>
</vxml>
In the example above, we are using one of the Tellme grammars,
Four_digits, to regulate the input. The grammar contains rules
that will cause the document to call the nomatch event unless
the user enters four numbers via the phone keypad or by voice. The
reprompt element repeats the last prompt, Please enter
your 4 digit pin code after telling the user that they've entered an
invalid PIN code. Tellme will keep reprompting the user as long as they keep
entering invalid input.
Of course, if the user is repeatedly entering invalid input, giving
them the same error message and prompt won't help the user any. In fact, it
would be downright user unfriendly. This is why the
nomatch element includes a count
attribute that allows us to give the user a different warning message each time
the nomatch event is called.
<nomatch count="1">Invalid pin code.
<reprompt/>
</nomatch>
<nomatch count="2">Please press or say exactly four numbers.
<reprompt/>
</nomatch>
<nomatch count="3">Too many attempts. Please call back
another time.
<exit/>
</nomatch>
Now, the second time the user provides bad input, we give them more
specific instructions, "Too many attempts. lease call back another
time." The third time the user provides bad input, we exit the
program.
No Input
Like handling invalid input, it's also critical to handle
no input. Tellme calls the noinput event when the user does not
provide any input after a prompt has been played.
<?xml version="1.0"?>
<vxml version="1.0" >
<form id="hello">
<field name="pin">
<grammar>
<![CDATA[
Four_digits
]]>
</grammar>
<prompt>Please enter your 4 digit pin code.</prompt>
<filled>
<submit next="http://www.webreference.com/cgi-bin/perl/20/pin.pl"/>
</filled>
<noinput>
<reprompt/>
</noinput>
<nomatch>Invalid pin code.
<reprompt/>
</nomatch>
</field>
</form>
</vxml>
Like the nomatch element, if you don't handle
the noinput event, your VoiceXML application will return an
error when it's called. Also, like nomatch, you can set
the count attribute so that a different message is played
each time the user fails to provide input.
<noinput count="1">No PIN entered.
<reprompt/>
</noinput>
<noinput count="2">You must enter your PIN number to proceed.
<reprompt/>
</noinput>
<noinput count="3">Please press or say exactly four numbers.
</noinput>
If the noinput event is called more than 3 times,
Tellme will continue to repeat the last noinput,
"Please press or say exactly four numbers.", until the user provides
some input.
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