youys
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ant

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<h2>PropertyHelper</h2>
<h3>Description</h3>
<p>This task is provided for the purpose of allowing the user to
<b>(a)</b> install a different PropertyHelper at runtime, or
<b>(b)</b> (hopefully more often) install one or more PropertyHelper Delegates into the
PropertyHelper active on the current Project. This is somewhat advanced 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.
<b>Since Ant 1.8.0</b></p>

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

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

<h4>PropertyHelper.Delegate</h4>
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.

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

<h5>Parameters</h5>
<table border="1" cellpadding="2" cellspacing="0"> 
  <tr>
    <td valign="top"><b>Attribute</b></td>
    <td valign="top"><b>Description</b></td>
    <td align="center" valign="top"><b>Required</b></td>
  </tr>
  <tr>
    <td valign="top">refid</td>
    <td valign="top">The <i>id</i> of a <code>PropertyHelper.Delegate</code> to install.</td>
    <td valign="top" align="center">Yes</td>
  </tr>
</table>

<h3>Examples</h3>

<p>Install a completely different PropertyHelper 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 PropertyEvaluator delegate
  (assuming <code>MyPropertyEvaluator implements
  PropertyHelper.PropertyEvaluator</code>).  Note that PropertyHelper
  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 PropertyEvaluator delegate using the refid 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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