XForms/Validation with Bind

Motivation

You want to validate a single field based on a rule and alert the user if they enter an invalid value.

Method

We will use an XForms bind expression:

  <xf:bind nodeset="PositiveDecimalAmount" 
      type="xs:decimal" 
      constraint=". > 0"/>

This last line says that if the current element is greater than zero then the rule passes and the field is valid.

Screen Image

Sample Code

   <html
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:xf="http://www.w3.org/2002/xforms" 
    xmlns:xs="http://www.w3.org/2001/XMLSchema" 
    >
    <head>
        <title>Validation With Bind</title>
        <style type="text/css">
        <![CDATA[
            body {
            font-family: Helvetica, sans-serif;
            }
        ]]>
        </style>
        <xf:model>
            <xf:instance xmlns="">
               <data>
                    <PositiveDecimalAmount>1.0</PositiveDecimalAmount>
                    <NegativeDecimalAmount>-1.0</NegativeDecimalAmount>
                </data>
            </xf:instance>
            
            <!-- note that the gt operator does not work and that the greater than character must be escaped.  -->
            <xf:bind nodeset="PositiveDecimalAmount" type="xs:decimal" required="false()" constraint=". &gt; 0"/>
            
            <!-- note that the lt operator does not work and that the less than character must be escaped.  -->
            <xf:bind nodeset="NegativeDecimalAmount" type="xs:decimal" required="false()" constraint=". &lt; 0"/>


        </xf:model>
    </head>
    <body>
        <h1>Validation With Bind</h1>
        <p>To pass this test the form must warn the user if they enter </p>
        
            <xf:input class="PositiveDecimalAmount" ref="PositiveDecimalAmount" incremental="true">
                <xf:label>Positive Decimal Amount:</xf:label>
                <xf:alert>Amount must be a positive decimal number.</xf:alert>
            </xf:input>
            <br/>
            <xf:input class="NegativeDecimalAmount" ref="NegativeDecimalAmount" incremental="true">
                <xf:label>Negative Decimal Amount:</xf:label>
                <xf:alert>Amount must be a negative decimal number.</xf:alert>
            </xf:input>
            <br/>
    </body>
</html>

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