A number of Zend Framework components are pluggable, and allow loading
of dynamic functionality by specifying a class prefix and path to class
files that are not necessarily on the include_path or do
not necessarily follow traditional naming conventions.
Zend_Loader_PluginLoader provides common functionality for
this process.
The basic usage of the PluginLoader follows Zend Framework
naming conventions of one class per file, using the underscore as a
directory separator when resolving paths. It allows passing an optional
class prefix to prepend when determining if a particular plugin class is
loaded. Additionally, paths are searched in LIFO order. Due to the LIFO
search and the class prefixes, this allows you to namespace your
plugins, and thus override plugins from paths registered earlier.
First, let's assume the following directory structure and class files, and that the toplevel directory and library directory are on the include_path:
application/
modules/
foo/
views/
helpers/
FormLabel.php
FormSubmit.php
bar/
views/
helpers/
FormSubmit.php
library/
Zend/
View/
Helper/
FormLabel.php
FormSubmit.php
FormText.php
Now, let's create a plugin loader to address the various view helper repositories available:
<?php
$loader = new Zend_Loader_PluginLoader();
$loader->addPrefixPath('Zend_View_Helper', 'Zend/View/Helper/')
->addPrefixPath('Foo_View_Helper', 'application/modules/foo/views/helpers')
->addPrefixPath('Bar_View_Helper', 'application/modules/bar/views/helpers');
?>
We can then load a given view helper using just the portion of the class name following the prefixes as defined when adding the paths:
<?php
// load 'FormText' helper:
$formTextClass = $loader->load('FormText'); // 'Zend_View_Helper_FormText';
// load 'FormLabel' helper:
$formLabelClass = $loader->load('FormLabel'); // 'Foo_View_Helper_FormLabel'
// load 'FormSubmit' helper:
$formSubmitClass = $loader->load('FormSubmit'); // 'Bar_View_Helper_FormSubmit'
?>
Once the class is loaded, we can now instantiate it.
![[Замечание]](/images/note.gif) |
Multiple paths may be registered for a given prefix |
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In some cases, you may use the same prefix for multiple paths.
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Paths may be defined at instantiation |
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You may optionally provide an array of prefix / path pairs (or prefix / paths -- plural paths are allowed) as a parameter to the constructor: <?php
$loader = new Zend_Loader_PluginLoader(array(
'Zend_View_Helper' => 'Zend/View/Helper/',
'Foo_View_Helper' => 'application/modules/foo/views/helpers',
'Bar_View_Helper' => 'application/modules/bar/views/helpers'
));
?>
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Zend_Loader_PluginLoader also optionally allows you to
share plugins across plugin-aware objects, without needing to
utilize a singleton instance. It does so via a static registry.
Indicate the registry name at instantiation as the second parameter
to the constructor:
<?php // Store plugins in static registry 'foobar': $loader = new Zend_Loader_PluginLoader(array(), 'foobar'); ?>
Other components that instantiate the PluginLoader
using the same registry name will then have access to already loaded
paths and plugins.
The example in the previous section shows how to add paths to a plugin loader. What if you want to determine the paths already loaded, or remove one or more?
getPaths($prefix = null)returns all paths as prefix / path pairs if no$prefixis provided, or just the paths registered for a given prefix if a$prefixis present.clearPaths($prefix = null)will clear all registered paths by default, or only those associated with a given prefix, if the$prefixis provided and present in the stack.removePrefixPath($prefix, $path = null)allows you to selectively remove a specific path associated with a given prefix. If no$pathis provided, all paths for that prefix are removed. If a$pathis provided and exists for that prefix, only that path will be removed.
Sometimes you simply want to determine if a plugin class has been
loaded before you perform an action. isLoaded() takes a
plugin name, and returns the status.
Another common use case for the PluginLoader is to
determine fully qualified plugin class names of loaded classes;
getClassName() provides this functionality. Typically,
this would be used in conjunction with isLoaded():
<?php
if ($loader->isLoaded('Adapter')) {
$class = $loader->getClassName('Adapter');
$adapter = call_user_func(array($class, 'getInstance'));
}
?>