Learn how to implement chain of responsibility design pattern

1. Chain-Of-Responsibility
Design Pattern

2. Overview
Objective
Learn how to use the Chain Of Responsibility design
pattern.
Requirements
 Basics of Protected Methods
 Basics of Abstract Classes
Estimated Time
6 minutes
www.prodigyview.com

3. Follow Along With Code
Example
1. Download a copy of the example code at
www.prodigyview.com/source.
2. Install the system in an environment you feel
comfortable testing in.
3. Proceed to examples/data/Command.php

4. What is the Chain –Of-
Responsibility?
The Chain-of-responsibility is a design pattern that has
command objects and processing objects. The command
objects iterates through the processing objects and executes
on the processing objects that can handle the request.
Translated into English, a method in on object is called and it
searches for other objects that can handle the methods
request.
In ProdigyView,, the chain-of-responsibility is a little different.
An object methods are ran through until the correct method is
found and then that method is executed.

5. Chain-of-Responsibility Visual
Call Method lookUp()
Method turnLeft();
Method turnRight();
Output Method lookUp();
Method lookDown();
Method turnAround()

6. Command in ProdigyView
The Chain-of-responsibility is implemented in
ProdigyView by extending the PVApplication or
PVStaticApplication.
Extend PVApplication
Required abstract function

7. Command Interpreter
So genius, you have a class that is full of protected methods
and no way to access them, how are we going to call them?
Well notice that our class extends PVApplication.
PVApplication contains a public method called the
commandInterpreter. The first argument will be the name of
the method to execute. Any other arguments after that will be
passed to the method.
PVApplication is an abstract class and the only method that is
required for you to implement is the defaultFunction(). This
will execute if no command is found. Let’s run some
commands.

8. Command Interpreter Example
The method that will be called
The arguements passed to the method

9. Command Interpreter Results
The results from passing those commands should look
like this.

10. The Not So Obvious
1. PVApplication extends PVObject which extends
PVPatterns. This means any object that extends
PVApplication with has use of all the other design
patterns as well the PVObject’s collections.
2. An object that extends PVApplication can be used as a
stand alone object or be integrated in ProdigyView’s
application system.

11. Challenge!
This is an optional challenge designed to help you better
understand the design pattern.
Create two classes that both have only protected methods
and extends PVApplication or PVStaticApplication. Create
at least 3 methods in each class.
Start the chain by calling one of the object’s command
interpreter, and have each method call the other objects
command interpreter until the default function is reached.

12. Summary
1. Have an object extend PVApplication
2. Create methods inside that object. They can be
protected or public if they are going to be called by the
commandInterpreter().
3. Execute a method inside that object by using the
commandInterpeter and having the first argument
passed be the name of the method and any other
variables behind it will be passed to the called method
as arguments.

13. API Reference
For a better understanding of the Collections and the
Iterator, check out the api at the two links below.
PVApplication
More Tutorials
For more tutorials, please visit:
http://www.prodigyview.com/tutorials
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