Archive for the 'Bridge' Category

PHP Bridge Pattern CMS

bridgeCMSA Flexible CMS

The previous post on the PHP Bridge Design pattern shows how a Bridge pattern has two connected but independent interfaces to make design flexibility for different online devices. This post explores how that same flexibility extends to making a Content Management System (CMS). Most of the Bridge participants in the design are unchanged or only slightly changed.

The major change in the Bridge design pattern actually makes it more in line with the original intention of the Bridge. The RefinedAbstraction participant (RefinedPage) no longer includes concrete content for the page. Instead, it provides the parameters for a client to add the content. This change adds flexibility and gives the developer more options than the original StandardPage class.

Two UIs and Multiple Clients

In order to make a decent CMS, you need to have at least two UIs:

  1. An Administrative UI for previewing and adding new content
  2. A User UI for viewing but not changing content

In creating the Administrative UI (HTML5/PHP/JavaScript), I had to use two PHP clients. One client is to preview the new data entered by the admin and the other client is to store the new data (after previewing and possibly editing it). Figure I provides a general overview of the UIs and the Clients that will use the Bridge pattern for a CMS:

Figure 1: User Interfaces and Clients

Figure 1: User Interfaces and Clients

The Administrative UI (BridgeCMSAdmin.html) uses the BridgeCMSAdminClient class for displaying different content and the StoreDataClient class for storing the information in a JSON file. An important condition to remember is that when using JSON files, you need to make their permissions available for reading and writing. (See the Memento II post and the special mini-post on setting permissions on Raspberry Pi systems.) Thus, the need for two clients; one for previewing new material and another for storing it in a JSON file. A lot of files are involved in this CMS; so take a look at the two different UIs and download the files for everything:
PlayPlayAdminDownload

To use the Administrator Module, follow these steps in the listed order:

  1. Type in Header data, select a graphic from the drop down menu, and then type in text for the body.
  2. Click a Desktop, Tablet or Phone radio button and then click Preview Page
  3. When you have everything the way you want it, First click Transfer to Storage and next click Store Data
  4. Now click the Play button and see the page you created.

In the admin UI, I used a drop down menu with only three selections for the graphic file since only three were set up. However, it would not be difficult to upload graphics and their file names. (See the post on uploading graphics using the Template Method.)

The UIs and their Clients

The main feature in creating a CMS is the Administrative UI. It calls two different clients for dealing with previews and persistent data storage. Unless you’re planning on a fairly long body text entry, the JSON file works fine. Look at the code below, and you can see that one of the issues is that the data that is entered for the preview must be transferred to a different form. It transferring the data is a simple task with a little JavaScript. The following script is all it takes:

?View Code JAVASCRIPT
function transferData(formNow)
{
    formNow.header.value = bridgeWork.header.value;
    formNow.graphic.value = bridgeWork.graphic.value;
    formNow.bodytext.value = bridgeWork.bodytext.value;
}

Stored in an external JS file, it was used only when the data was going to be stored; however, before storing it, it had to be transferred from the bridgeWork form to the dataStore form.

< !DOCTYPE html>
<html>
<head>
    <link rel="stylesheet" type="text/css" href="cmsbridge.css"/>
    <script src="formXfer.js"> </script>
    <title>CMS Admin Bridge</title>
</head>
<body>
    <h2>Enter Update Data</h2>
    <form method="post" name="bridgeWork" action="BridgeCMSAdminClient.php">
        <input type="text" name="header"/>&nbsp;Header<br />
        <select name="graphic">
            <option>Select Travel Graphic</option>
            <option value="nephpAir.jpg">Air</option>
            <option value="nephpTrain.jpg">Train</option>
            <option value="nephpShip.jpg">Ship</option>
        </select>
        <br />
        Enter the text for the body below:<br />
        <textarea name="bodytext" cols="48" rows="12"></textarea><p></p>
        <h3>Preview New Data</h3>
        <input type="radio" name="device" value="Desktop"/>&nbsp;Desktop<br />
        <input type="radio" name="device" value="Tablet"/>&nbsp;Tablet<br />
        <input type="radio" name="device" value="Phone"/>&nbsp;Phone<p></p>
        <input type="submit" name="deliver" value="Preview Page"/>
    </form>
 
    <h3>Store New Data</h3>
    <form method="post" name="dataStore" action="StoreDataClient.php">
        <input type="hidden" name="header"/>
        <input type="hidden" name="graphic"/>
        <input type="hidden" name="bodytext"/>
        <button type="button" onclick="transferData(dataStore)">Transfer to Storage</button>
        <input type="submit" name="jsonstore" value="Store Data"/>
    </form>
 
</body>
</html>

Then using build-in PHP JSON json_encode() method, the data were placed into an array and stored in the JSON file. This was done using the StoreDataClient class:

< ?php
class StoreDataClient
{
    private static $dataStorage=array();
    private static $jsonFile="content.json";
    //Client stores data
    public static function store()
    {
        if (isset($_POST['jsonstore']))
        {   
            self::setStore();
        }
      file_put_contents(self::$jsonFile,json_encode(self::$dataStorage,JSON_UNESCAPED_UNICODE));
    }
 
    private static function setStore()
    {
        //Pushes data from HTML to array
        array_push(self::$dataStorage,$_POST['header'],$_POST['graphic'],$_POST['bodytext']);
    }
}
StoreDataClient::store();
?>

Just in case you’re wondering why a single PHP client class was not used for both preview and storage, it’s simple:

OOP Principle: Each class should have only a single responsibility.

We don’t want to cram classes; so each responsibility has its own class. (Click below to see the other client and the rest of the CMS.)
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PHP Bridge Design Pattern

armeniaTwo Interfaces

The intent of the Bridge pattern is to decouple an abstraction from its implementation so that the two can vary independently. (GoF 151) If you don’t think about that much, it sounds like a good idea to keep an application from grinding its gears when a change is made in either the abstraction or implementation. The Freemans (Head First Design Patterns, pp. 612-613) have a great example—a universal remote control. The remote control is the abstraction and a TV set is the implementor. Concrete implementors are the different brands of TVs. As new technology arises, the remote control can be updated with new gizmos. Likewise, the TV sets can also be updated and different brands will have their own unique features. A good Bridge design will allow each to be changed without breaking the other. So far so good.

An Abstraction Has-A Implementor

About six years ago, I started looking at different Bridge design pattern examples. I ran into examples that were examples of something but did not seem to be Bridge patterns. (One was nothing more than a single interface with two different implementations. The coder explained, See, that’s a bridge. I sat there with question marks floating above my head like some cartoon character.) The GoF intent statement and Freeman example were quite clear. However, the Abstraction interface and the Implementor interface, either of which could be an abstract class or interface structure, were bridged by the abstraction having-a implementor. To fully understand a Bridge pattern, you need to understand the relationship known as a bridge between the Abstraction and Implementor participants. First, though, see what the results are by pressing the Play button and Download the files:
PlayDownload

For an overview, take a look at Figure 1. The top half is the structure laid out by The Gang of Four—the generic class diagram for a Bridge pattern. The bottom half is the PHP implementation that addresses a common issue: Variation in the content of a Web page and the structure of a Web page. By having two interfaces, either can change independently of the other. The example shows a Web page with variable content that is displayed in desktop and mobile devices.

Figure 1: Bridge Class diagrams

Figure 1: Bridge Class diagrams


One of the important features of the Bridge pattern turns out to be quite subtle and easily overlooked.

The key method (Operation()) in the Abstraction participant is a concrete one.

In the example for this post, the IPage abstract class includes the buildPage() method. The buildPage() method uses a concrete implementation of the Implementor participant, (IDevice). You can see how the method is implemented in the IPage abstract class:

< ?php
abstract class IPage 
{
    //Low-level
    abstract function doDevice(IDevice $deviceNow);
    //High-level
    protected function buildPage()
    {
        echo $this->deviceSelected->buildDevice($this->header,$this->graphic,$this->body);
    }
    //Properties
    protected $header, $graphic, $body, $deviceSelected;
}
?>

As you can see, the abstract function doDevice() expects an IDevice object as a parameter. The $deviceSelected property is one that will be assigned a concrete Implementor (IDevice). So, in the sense that both an abstract reference using code hinting and a concrete use of an implemented IDevice are part of the IPage abstract class, it can be said to “have a” Implementor (IDevice). (Click below to see the rest of the Bridge pattern.)
Continue reading ‘PHP Bridge Design Pattern’

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