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<td><h1>CodeIgniter User Guide Version 2.1.3</h1></td>
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Hooks - Extending the Framework Core
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<h1>Hooks - Extending the Framework Core</h1>
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<p>CodeIgniter's Hooks feature provides a means to tap into and modify the inner workings of the framework without hacking the core files.
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When CodeIgniter runs it follows a specific execution process, diagramed in the <a href="../overview/appflow.html">Application Flow</a> page.
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There may be instances, however, where you'd like to cause some action to take place at a particular stage in the execution process.
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For example, you might want to run a script right before your controllers get loaded, or right after, or you might want to trigger one of
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your own scripts in some other location.
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<h2>Enabling Hooks</h2>
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<p>The hooks feature can be globally enabled/disabled by setting the following item in the <kbd>application/config/config.php</kbd> file:</p>
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<code>$config['enable_hooks'] = TRUE;</code>
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<h2>Defining a Hook</h2>
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<p>Hooks are defined in <dfn>application/config/hooks.php</dfn> file. Each hook is specified as an array with this prototype:</p>
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$hook['pre_controller'] = array(<br />
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'class' => 'MyClass',<br />
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'function' => 'Myfunction',<br />
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'filename' => 'Myclass.php',<br />
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'filepath' => 'hooks',<br />
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'params' => array('beer', 'wine', 'snacks')<br />
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);</code>
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<p><strong>Notes:</strong><br />The array index correlates to the name of the particular hook point you want to
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use. In the above example the hook point is <kbd>pre_controller</kbd>. A list of hook points is found below.
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The following items should be defined in your associative hook array:</p>
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<li><strong>class</strong> The name of the class you wish to invoke. If you prefer to use a procedural function instead of a class, leave this item blank.</li>
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<li><strong>function</strong> The function name you wish to call.</li>
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<li><strong>filename</strong> The file name containing your class/function.</li>
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<li><strong>filepath</strong> The name of the directory containing your script. Note: Your script must be located in a directory INSIDE your <kbd>application</kbd> folder, so the file path is relative to that folder. For example, if your script is located in <dfn>application/hooks</dfn>, you will simply use <samp>hooks</samp> as your filepath. If your script is located in <dfn>application/hooks/utilities</dfn> you will use <samp>hooks/utilities</samp> as your filepath. No trailing slash.</li>
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<li><strong>params</strong> Any parameters you wish to pass to your script. This item is optional.</li>
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<h2>Multiple Calls to the Same Hook</h2>
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<p>If want to use the same hook point with more then one script, simply make your array declaration multi-dimensional, like this:</p>
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$hook['pre_controller']<kbd>[]</kbd> = array(<br />
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'class' => 'MyClass',<br />
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'function' => 'Myfunction',<br />
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'filename' => 'Myclass.php',<br />
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'filepath' => 'hooks',<br />
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'params' => array('beer', 'wine', 'snacks')<br />
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);<br />
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$hook['pre_controller']<kbd>[]</kbd> = array(<br />
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'class' => 'MyOtherClass',<br />
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'function' => 'MyOtherfunction',<br />
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'filename' => 'Myotherclass.php',<br />
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'filepath' => 'hooks',<br />
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'params' => array('red', 'yellow', 'blue')<br />
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);</code>
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<p>Notice the brackets after each array index:</p>
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<code>$hook['pre_controller']<kbd>[]</kbd></code>
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<p>This permits you to have the same hook point with multiple scripts. The order you define your array will be the execution order.</p>
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<p>The following is a list of available hook points.</p>
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<li><strong>pre_system</strong><br />
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Called very early during system execution. Only the benchmark and hooks class have been loaded at this point. No routing or other processes have happened.</li>
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<li><strong>pre_controller</strong><br />
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Called immediately prior to any of your controllers being called. All base classes, routing, and security checks have been done.</li>
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<li><strong>post_controller_constructor</strong><br />
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Called immediately after your controller is instantiated, but prior to any method calls happening.</li>
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<li><strong>post_controller</strong><br />
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Called immediately after your controller is fully executed.</li>
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<li><strong>display_override</strong><br />
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Overrides the <dfn>_display()</dfn> function, used to send the finalized page to the web browser at the end of system execution. This permits you to
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use your own display methodology. Note that you will need to reference the CI superobject with <dfn>$this->CI =& get_instance()</dfn> and then the finalized data will be available by calling <dfn>$this->CI->output->get_output()</dfn></li>
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<li><strong>cache_override</strong><br />
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Enables you to call your own function instead of the <dfn>_display_cache()</dfn> function in the output class. This permits you to use your own cache display mechanism.</li>
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<li><strong>post_system</strong><br />
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Called after the final rendered page is sent to the browser, at the end of system execution after the finalized data is sent to the browser.</li>
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