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Designing Interfaces in PHP

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Autoloading

6:23 with Alena Holligan

Instead of including each class file individually, we are going to make use of another great component of Object-Oriented Programming: autoloading. Autoloading is triggered when a class is not found. Before the system throws an error, we can specify a function which will look for the class and automatically include that file when needed.

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    The project we're building, we use many different classes and interfaces. 0:00
    All of which need to be included before they can be used. 0:05
    Instead of adding each file individually, we're going to make 0:09
    use of another great component of object oriented programming, autoloading. 0:12
    Autoloading is triggered when a class is not found. 0:18
    Before the system throws an error, we can specify a function which will look for 0:22
    the class, and automatically include that file when needed. 0:26
    Let's launch the workspace attached to this video and 0:31
    start by creating our first class. 0:34
    We're going to put all our classes and interfaces in our source directory. 0:37
    Let's create a new folder named classes. 0:42
    We'll then create a new file, Named collection.php. 0:49
    For now, we're just going to start with an empty class. 0:58
    In the index.php file, let's attempt to instantiate this new class. 1:08
    New Collection. 1:18
    Now, we can preview the site in a browser. 1:21
    We see an error telling us that the Class Collection cannot be found. 1:27
    If we go back to WorkSpaces, we could require this new class file first. 1:31
    This would require us to include each class file individually. 1:49
    So let's set up an autoloader instead. 1:53
    First, we're going to create a config file within the source directory. 1:56
    We'll use this for 2:02
    all the shared functionality we'll need throughout our application. 2:04
    We can then include this file on any page. 2:08
    We're ready to create an autoload function. 2:25
    Let's take a look at the documentation. 2:28
    Php autoload. 2:34
    The first result tells us that it's preferred to use 2:40
    the spl_autoload_register function. 2:44
    So let's go there. 2:47
    Instead of including a class specifically, 2:49
    spl_autoload_register will trigger a function when a class is not available. 2:51
    These triggers are sometimes referred to as listeners, 2:57
    because they passively listen for some specific event to happen. 3:01
    And when it does, they'll trigger a reaction. 3:05
    For a trigger to work, we need to register this functionality. 3:09
    We used a function spl_autoload_register to tell PHP 3:14
    which function to use when a class or an interface is not found. 3:18
    Let's scroll to the first example. 3:23
    We build our function, then we register that function with spl_autoload_register. 3:28
    php will automatically pass the name of the class that it is attempting to 3:34
    instantiate. 3:38
    Unlike the example here, I want to be able to organize my classes and 3:40
    interfaces into subdirectories. 3:44
    To do this, let's use another built in function named glob. 3:46
    Glob finds the pathnames matching a pattern. 3:54
    We can use the GLOB_ONLYDIR to return only 3:57
    directory entities which match the pattern. 4:00
    Let's go back to WorkSpaces. 4:05
    We'll create our new function, autoloader, and we'll accept the class name. 4:12
    Then we'll use a foreach loop, With our glob, 4:26
    The current directory, And all entries. 4:33
    We use the GLOB_ONLYDIR flag, and then as $dir. 4:43
    Now, we can check if (file_exists, 4:57
    Our "$dir/", The $class_name, '.php'. 5:04
    Then we can require_once, The "$dir/", 5:16
    $class_name, '.php'. 5:23
    Then we can use the break; to stop the foreach loop after a file has been found. 5:30
    Next, we need to register this function, 5:36
    spl_autoload_register('autoloader. 5:41
    Now, when a class is found before an error is thrown, our autoload function will be 5:50
    triggered, which automatically adds the class for us using the require statement. 5:55
    Lets go back to our preview. 6:02
    We no longer get an error because the class has been included with our 6:06
    autoloader. 6:10
    Now, that we have an autoloader setup, 6:11
    we no longer have to worry about including any of our future classes or 6:13
    interfaces, as long as they're stored in a directory, below the source directory. 6:18

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