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31 <td><h1>CodeIgniter User Guide Version 2.0.2</h1></td>
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60 <p>Controllers are the heart of your application, as they determine how HTTP requests should be handled.</p>
64 <li><a href="#what">What is a Controller?</a></li>
65 <li><a href="#hello">Hello World</a></li>
66 <li><a href="#functions">Functions</a></li>
67 <li><a href="#passinguri">Passing URI Segments to Your Functions</a></li>
68 <li><a href="#default">Defining a Default Controller</a></li>
69 <li><a href="#remapping">Remapping Function Calls</a></li>
70 <li><a href="#output">Controlling Output Data</a></li>
71 <li><a href="#private">Private Functions</a></li>
72 <li><a href="#subfolders">Organizing Controllers into Sub-folders</a></li>
73 <li><a href="#constructors">Class Constructors</a></li>
74 <li><a href="#reserved">Reserved Function Names</a></li>
79 <h2>What is a Controller?</h2>
81 <p><dfn>A Controller is simply a class file that is named in a way that can be associated with a URI.</dfn></p>
83 <p>Consider this URI:</p>
85 <code>example.com/index.php/<var>blog</var>/</code>
87 <p>In the above example, CodeIgniter would attempt to find a controller named <dfn>blog.php</dfn> and load it.</p>
89 <p><strong>When a controller's name matches the first segment of a URI, it will be loaded.</strong></p>
92 <h2>Let's try it: Hello World!</h2>
94 <p>Let's create a simple controller so you can see it in action. Using your text editor, create a file called <dfn>blog.php</dfn>, and put the following code in it:</p>
97 <textarea class="textarea" style="width:100%" cols="50" rows="10">
99 class Blog extends CI_Controller {
101 public function index()
111 <p>Then save the file to your <dfn>application/controllers/</dfn> folder.</p>
113 <p>Now visit the your site using a URL similar to this:</p>
115 <code>example.com/index.php/<var>blog</var>/</code>
117 <p>If you did it right, you should see <samp>Hello World!</samp>.</p>
119 <p>Note: Class names must start with an uppercase letter. In other words, this is valid:</p>
122 class <var>Blog</var> extends CI_Controller {<br />
127 <p>This is <strong>not</strong> valid:</p>
130 class <var>blog</var> extends CI_Controller {<br />
135 <p>Also, always make sure your controller <dfn>extends</dfn> the parent controller class so that it can inherit all its functions.</p>
139 <a name="functions"></a>
142 <p>In the above example the function name is <dfn>index()</dfn>. The "index" function is always loaded by default if the
143 <strong>second segment</strong> of the URI is empty. Another way to show your "Hello World" message would be this:</p>
145 <code>example.com/index.php/<var>blog</var>/<samp>index</samp>/</code>
147 <p><strong>The second segment of the URI determines which function in the controller gets called.</strong></p>
149 <p>Let's try it. Add a new function to your controller:</p>
152 <textarea class="textarea" style="width:100%" cols="50" rows="15">
154 class Blog extends CI_Controller {
156 public function index()
161 public function comments()
163 echo 'Look at this!';
169 <p>Now load the following URL to see the <dfn>comment</dfn> function:</p>
171 <code>example.com/index.php/<var>blog</var>/<samp>comments</samp>/</code>
173 <p>You should see your new message.</p>
175 <a name="passinguri"></a>
176 <h2>Passing URI Segments to your Functions</h2>
178 <p>If your URI contains more then two segments they will be passed to your function as parameters.</p>
180 <p>For example, lets say you have a URI like this:</p>
182 <code>example.com/index.php/<var>products</var>/<samp>shoes</samp>/<kbd>sandals</kbd>/<dfn>123</dfn></code>
184 <p>Your function will be passed URI segments 3 and 4 ("sandals" and "123"):</p>
188 class Products extends CI_Controller {<br />
190 public function shoes($sandals, $id)<br />
191 {<br />
192 echo $sandals;<br />
193 echo $id;<br />
194 }<br />
199 <p class="important"><strong>Important:</strong> If you are using the <a href="routing.html">URI Routing</a> feature, the segments
200 passed to your function will be the re-routed ones.</p>
203 <a name="default"></a>
204 <h2>Defining a Default Controller</h2>
206 <p>CodeIgniter can be told to load a default controller when a URI is not present,
207 as will be the case when only your site root URL is requested. To specify a default controller, open
208 your <dfn>application/config/routes.php</dfn> file and set this variable:</p>
210 <code>$route['default_controller'] = '<var>Blog</var>';</code>
212 <p>Where <var>Blog</var> is the name of the controller class you want used. If you now load your main index.php file without
213 specifying any URI segments you'll see your Hello World message by default.</p>
217 <a name="remapping"></a>
218 <h2>Remapping Function Calls</h2>
220 <p>As noted above, the second segment of the URI typically determines which function in the controller gets called.
221 CodeIgniter permits you to override this behavior through the use of the <kbd>_remap()</kbd> function:</p>
223 <code>public function _remap()<br />
225 // Some code here...<br />
228 <p class="important"><strong>Important:</strong> If your controller contains a function named <kbd>_remap()</kbd>, it will <strong>always</strong>
229 get called regardless of what your URI contains. It overrides the normal behavior in which the URI determines which function is called,
230 allowing you to define your own function routing rules.</p>
232 <p>The overridden function call (typically the second segment of the URI) will be passed as a parameter to the <kbd>_remap()</kbd> function:</p>
234 <code>public function _remap(<var>$method</var>)<br />
236 if ($method == 'some_method')<br />
237 {<br />
238 $this->$method();<br />
239 }<br />
240 else<br />
241 {<br />
242 $this->default_method();<br />
243 }<br />
246 <p>Any extra segments after the method name are passed into <kbd>_remap()</kbd> as an optional second parameter. This array can be used in combination with PHP's <a href="http://php.net/call_user_func_array">call_user_func_array</a> to emulate CodeIgniter's default behavior.</p>
248 <code>public function _remap($method, $params = array())<br />
250 $method = 'process_'.$method;<br />
251 if (method_exists($this, $method))<br />
252 {<br />
253 return call_user_func_array(array($this, $method), $params);<br />
254 }<br />
255 show_404();<br />
259 <a name="output"></a>
260 <h2>Processing Output</h2>
262 <p>CodeIgniter has an output class that takes care of sending your final rendered data to the web browser automatically. More information on this can be found in the
263 <a href="views.html">Views</a> and <a href="../libraries/output.html">Output class</a> pages. In some cases, however, you might want to
264 post-process the finalized data in some way and send it to the browser yourself. CodeIgniter permits you to
265 add a function named <dfn>_output()</dfn> to your controller that will receive the finalized output data.</p>
267 <p><strong>Important:</strong> If your controller contains a function named <kbd>_output()</kbd>, it will <strong>always</strong>
268 be called by the output class instead of echoing the finalized data directly. The first parameter of the function will contain the finalized output.</p>
270 <p>Here is an example:</p>
273 public function _output($output)<br />
275 echo $output;<br />
278 <p class="important">Please note that your <dfn>_output()</dfn> function will receive the data in its finalized state. Benchmark and memory usage data will be rendered,
279 cache files written (if you have caching enabled), and headers will be sent (if you use that <a href="../libraries/output.html">feature</a>)
280 before it is handed off to the _output() function.<br />
282 To have your controller's output cached properly, its <dfn>_output()</dfn> method can use:<br />
284 <code>if ($this->output->cache_expiration > 0)<br />
286 $this->output->_write_cache($output);<br />
289 If you are using this feature the page execution timer and memory usage stats might not be perfectly accurate
290 since they will not take into acccount any further processing you do. For an alternate way to control output <em>before</em> any of the final processing is done, please see
291 the available methods in the <a href="../libraries/output.html">Output Class</a>.</p>
293 <a name="private"></a>
294 <h2>Private Functions</h2>
297 <p>In some cases you may want certain functions hidden from public access. To make a function private, simply add an
298 underscore as the name prefix and it will not be served via a URL request. For example, if you were to have a function like this:</p>
301 private function _utility()<br />
303 // some code<br />
306 <p>Trying to access it via the URL, like this, will not work:</p>
308 <code>example.com/index.php/<var>blog</var>/<samp>_utility</samp>/</code>
312 <a name="subfolders"></a>
313 <h2>Organizing Your Controllers into Sub-folders</h2>
315 <p>If you are building a large application you might find it convenient to organize your controllers into sub-folders. CodeIgniter permits you to do this.</p>
317 <p>Simply create folders within your <dfn>application/controllers</dfn> directory and place your controller classes within them.</p>
319 <p><strong>Note:</strong> When using this feature the first segment of your URI must specify the folder. For example, lets say you have a controller
322 <code>application/controllers/<kbd>products</kbd>/shoes.php</code>
324 <p>To call the above controller your URI will look something like this:</p>
326 <code>example.com/index.php/products/shoes/show/123</code>
328 <p>Each of your sub-folders may contain a default controller which will be
329 called if the URL contains only the sub-folder. Simply name your default controller as specified in your
330 <dfn>application/config/routes.php</dfn> file</p>
333 <p>CodeIgniter also permits you to remap your URIs using its <a href="routing.html">URI Routing</a> feature.</p>
336 <h2><a name="constructors"></a>Class Constructors</h2>
339 <p>If you intend to use a constructor in any of your Controllers, you <strong>MUST</strong> place the following line of code in it:</p>
341 <code>parent::__construct();</code>
343 <p>The reason this line is necessary is because your local constructor will be overriding the one in the parent controller class so we need to manually call it.</p>
347 class <kbd>Blog</kbd> extends CI_Controller {<br />
349 public function <kbd>__construct()</kbd><br />
350 {<br />
351 <var>parent::__construct();</var><br />
352 // Your own constructor code<br />
353 }<br />
357 <p>Constructors are useful if you need to set some default values, or run a default process when your class is instantiated.
358 Constructors can't return a value, but they can do some default work.</p>
360 <a name="reserved"></a>
361 <h2>Reserved Function Names</h2>
363 <p>Since your controller classes will extend the main application controller you
364 must be careful not to name your functions identically to the ones used by that class, otherwise your local functions
365 will override them. See <a href="reserved_names.html">Reserved Names</a> for a full list.</p>
369 <p>That, in a nutshell, is all there is to know about controllers.</p>
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