[cvs] [Wiki] changed: Doc/Dev/DesignPatterns

[Jan Schneider]

jan  Sun, 07 Aug 2005 13:19:47 -0700

Modified page: http://wiki.horde.org/Doc/Dev/DesignPatterns
New Revision:  1.1
Change log:  Copied from bostonphp2005-06 presentation

@@ -1 +1,185 @@
++ Design Patterns
+
+[[toc]]
+
+++ What are design patterns?
+
+> "Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice."
+> 
+> ? Christopher Alexander, talking about buildings and towns
+
+* Many common programming problems
+* They've been solved over and over again
+* Recognize which problems are common
+* Name them to create a common vocabulary
+* Patterns are blueprints
+* They are meant to be modified
+* Not all suspension bridges are the same
+
+++ What do patterns not do?
+
+* Patterns are not rules
+* Patterns are not implementations!
+
+++ When to use them
+
+* When the Problem they solve is a problem you have ...
+* ... and when the Consequences are acceptable
+* Solve problems you have, not problems you think you might have
+
+++ Common Patterns
+
+* Abstract Factory
+* Singleton
+* Observer
+* Model/View/Controller
+
++++ Abstract Factory
+
+* Provides an interface for creating one of a family of objects without specifying that object's concrete class name.
+* Example: DB::connect()
+
+<code type="php">
+require_once 'DB.php';
+
+$type = 'mysql';
+$options = array(...);
+$dbh = &DB::connect($type, $options);
+</code>
+
+++++ Implementing Abstract Factory
+
+<code type="php">
+    function &factory($type)
+    {
+        @include_once("DB/${type}.php");
+
+        $classname = "DB_${type}";
+
+        if (!class_exists($classname)) {
+            return PEAR::raiseError(null, DB_ERROR_NOT_FOUND,
+                                    null, null, null, 'DB_Error', true);
+        }
+
+        return $obj =& new $classname;
+    } 
+</code>
+
++++ Singleton
+
+* Ensures that there is only ever one instance of a class.
+* Can only be implemented as a suggestion in PHP4
+
+++++ Implementing Singleton
+
+<code type="php">
+    function &singleton()
+    {
+        static $registry;
+
+        if (!isset($registry)) {
+            $registry = new Registry();
+        }
+
+        return $registry;
+    }
+</code>
+
+++++ Implementing Singleton in PHP5
+
+PHP5's improved object model allows a better singleton implementation:
+
+<code type="php">
+    /**
+     * The one instance.
+     */
+    static private $instance = false;
+
+    /**
+     * Make the constructor private.
+     */
+    private function __construct() {}
+
+    /**
+     * Use this static method to get at the one instance.
+     */
+    static public function singleton()
+    {
+        if (!self::$instance) {
+            self::$instance = new Singleton();
+        }
+        return self::$instance;
+    }
+</code>
+
++++ Observer
+
+* Also called Subject-Observer, Listener, or Publish-Subscribe
+* Let an arbitrary number of objects react to state changes
+
+++++ Implementing Observer: Subject
+
+<code type="php">
+    function attach(&$observer)
+    {
+        $this->_observers[$observer->getId()] =& $observer;
+    }
+
+    function detach(&$observer)
+    {
+        unset($this->_observers[$observer->getId()]);
+    }
+
+    function notify()
+    {
+        foreach ($this->_observers as &$observer) {
+            $observer->update($this);
+        }
+    }
+</code>
+
+++++ Implementing Observer: Observer
+
+<code type="php">
+    function update(&$subject)
+    {
+        // Do what needs to be done.
+    }
+</code>
+
++++ Model/View/Controller
+
+* MVC is a specialized Observer pattern, with Composite and Strategy completing the picture
+* Observer describes how Views and Models interact
+* Composite lets Views be made up of other Views
+* Strategy lets Views use different Controllers
+
+++++ MVC: Model/View
+
+* Think of structured HTML as a Model, and CSS as a View
+* Goal is to completely seperate data and logic from presentation
+* Allows redesigns or new views (different stylesheet) without changing the Model
+
+++++ MVC: View Compositing
+
+* When Smalltalk-80 introduced MVC it had a !CompositeView
+* The Composite pattern solves the problem of wanting to treat groups of objects like individual objects
+
+++++ MVC: View/Controller
+
+* The Controller decides how a View handles user input
+* Think of a command line interface, web interface, and web services as potential Controllers
+* Controllers take user input and give them to both Views and Models as appropriate
+
+++ PHP Implementations
+
+* http://www.google.com/search?q=php+mvc ... numerous
+* [http://phrame.sourceforge.net/ Phrame]
+* [http://www.tonybibbs.com/index.php?topic=MVCnPHP MVCnPHP]
+
+++ Some Resources
+
+* The [http://c2.com/ppr/ Portland Pattern Repository] (the original wiki)
+* [http://www.phparchitect.com/ php|architect]
+* [http://www.phppatterns.com/ phpPatterns.com] (not updated recently)