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Extending Object-Oriented PHP

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Adding Child Features

5:18 with Alena Holligan

A child class will perform all the same functions and utilize the same properties as the parent class. Additionally, a child may add its own attributes and abilities.

Remember that the parent class will NOT know about any properties or methods added to the child.

Documentation

  • strip_tags() - Strip HTML and PHP tags from a string. You can use the optional second parameter to specify tags which should not be stripped.
  • trim() - Strip whitespace (or other characters) from the beginning and end of a string
  • get_class() - Returns the name of the class of an object
  • is_a() - Checks if the object is of this class or has this class as one of its parents

Other Option

HTML Purifier

Additional Features You Could "extend" a Listing

  • logo
  • dates
  • code of conduct
  • call for papers

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    As a child of listening basic, the listing premium class will perform 0:00
    all the same functions and utilize the same properties as the parent class. 0:04
    Additionally a child may add it's own attributes and abilities. 0:09
    This is where extending comes in. 0:14
    There are many additional features that we could add to extend the premium listing, 0:16
    such as a description, logo, dates, code of conduct and call for papers. 0:22
    For this project I’m going to add a description, but go ahead and 0:27
    add your own features when we’re done. 0:31
    The first thing we need to do is create a new property with it's getters and 0:34
    setters. 0:37
    Private $description;. 0:38
    Let's copy the title getter and setters from the ListingBasic class. 0:43
    Now we can replace title with description. 0:55
    Let's test this out on our index page. 1:10
    We'll add a new object named test, and we'll set this = new ListingPremium(). 1:16
    Now let's move our display out of the for each loop. 1:25
    Now we can add a description to the test on the index page. 1:35
    We'll set this to My description. 1:42
    Now, let's check this out in the browser. 1:49
    Whoops, I forgot to change listing to test. 1:53
    Let's try that again. 2:03
    Great, our test listing has the new description property. 2:07
    Let's add a little more. 2:12
    I want to allow my description to accept certain tags. 2:14
    There are many different ways to do this, but 2:17
    I'm going to use the strip tags function. 2:19
    So let's check out the documentation. 2:21
    You can use the optional second parameter to specify tags, 2:31
    which should not be stripped. 2:35
    You specify a string with a simple form of the tags you wish to allow. 2:38
    Let's create a new protected property. 2:43
    Protected $allowed_tags, 2:48
    and we'll set this to 2:54
    for 2:58
    emphasis, 3:05
    That will give us a decent list. 3:12
    Now we need to change the setter. 3:20
    We've been using the filter_var to sanitize the information coming in. 3:23
    This allows us to safely accept user data. 3:27
    Instead of filter_var, 3:29
    we're going to use the strip_tags function to strip all but a few simple tags. 3:31
    For the second parameter, 3:42
    we specify our allowed tags $this->allowed_tags. 3:45
    Let's go back to index.php, and add some tags to our description. 3:52
    Good tags, and- 4:03
    Bad tags. 4:20
    Now, let's test this in a browser again. 4:25
    You can see that the description left the B tags but removed the link. 4:33
    Because the A tag is not one of the allowed tags. 4:37
    Remember, the set description method is specific to our listing premium class and 4:41
    our listing basic class will not be affected. 4:46
    Let's try changing this test to use our ListingBasic class. 4:49
    Now we get a call to undefined method on our ListingBasics class, 5:01
    because it does not know about the set description method that 5:05
    only applies to a listing premium object. 5:09
    Let's change this back to listing premium. 5:13

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