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<title>PropertyHelper Task</title>
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<h2>PropertyHelper</h2>
<p><em>Since Ant 1.8.0</em></p>
<h3>Description</h3>
<p>This task is provided for the purpose of allowing the user to <strong>(a)</strong> install a
different <code>PropertyHelper</code> at runtime, or <strong>(b)</strong> (hopefully more often)
install one or more <code>PropertyHelper</code> Delegates into the <code>PropertyHelper</code>
active on the current <code>Project</code>. This is somewhat advanced Apache Ant usage and assumes a
working familiarity with the modern Ant APIs. See the description of
Ant's <a href="../properties.html#propertyHelper">Property Helper</a> for more information.</p>

<h3>Parameters specified as nested elements</h3>

<h4>PropertyHelper</h4>
<p>You may specify exactly one configured <code>org.apache.tools.ant.PropertyHelper</code>
instance.</p>

<h4>PropertyHelper.Delegate</h4>
<p>You may specify, either in conjunction with a new <code>PropertyHelper</code> or not, one or more
configured implementations of the <code>org.apache.tools.ant.PropertyHelper.Delegate</code>
interface. A deeper understanding of the API is required here, however, as <code>Delegate</code> is
a marker interface only: the nested arguments must implement a <code>Delegate</code> subinterface in
order to do anything meaningful.</p>

<h4>delegate</h4>
<p>A generic <code>&lt;delegate&gt;</code> element which can use project references is also
provided:</p>

<h5>Parameters</h5>
<table class="attr">
  <tr>
    <th>Attribute</th>
    <th>Description</th>
    <th>Required</th>
  </tr>
  <tr>
    <td>refid</td>
    <td>The <var>id</var> of a <code>PropertyHelper.Delegate</code> to install.</td>
    <td>Yes</td>
  </tr>
</table>

<h3>Examples</h3>

<p>Install a completely different <code>PropertyHelper</code> implementation
(assuming <code>MyPropertyHelper extends PropertyHelper</code>):</p>

<pre>
&lt;componentdef classname="org.example.MyPropertyHelper"
              name="mypropertyhelper"/>
&lt;propertyhelper>
  &lt;mypropertyhelper/>
&lt;/propertyhelper>
</pre>

<p>Add a new <code>PropertyEvaluator</code> delegate (assuming <code>MyPropertyEvaluator implements
PropertyHelper.PropertyEvaluator</code>).  Note that <code>PropertyHelper</code> uses the configured
delegates in LIFO order.  I.e. the delegate added by this task will be consulted before any
previously defined delegate and in particular before the built-in ones.</p>

<pre>
&lt;componentdef classname="org.example.MyPropertyEvaluator"
              name="mypropertyevaluator"/>
&lt;propertyhelper>
  &lt;mypropertyevaluator/>
&lt;/propertyhelper>
</pre>

<p>Add a new <code>PropertyEvaluator</code> delegate using the <var>refid</var> syntax:</p>

<pre>
&lt;typedef classname="org.example.MyPropertyEvaluator"
         name="mypropertyevaluator"/>
&lt;mypropertyevaluator id="evaluator"/>
&lt;propertyhelper>
  &lt;delegate refid="evaluator"/>
&lt;/propertyhelper>
</pre>

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