Learn how to implement the observer design pattern.

1. Observer Design Pattern

2. Overview
Objective
Learn how to use the observer design pattern.
Requirements
 Basics of ProdigyView
Estimated Time
8 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/design/Observers.php

4. What Are Observers
Observers are a design pattern, most commonly used in
event driven programming, where an object has a list of
observers and the observers are notified of a state
change.
A simpler explanation would be when a function is
executed, a list of other functions is automatically
executed.

5. Observers Visual
MyObject::doSomething
Method doSomething
executes. Notify observers
execution has taken place.
Output

6. PVPatterns and
PVStaticPatterns
The classes that contain the methods for using observers is the
PVPatterns and PVStaticPatterns classes.
PVPatterns is for instances and PVStaticPatterns is for static
methods.
Both PVObject and PVStaticObject extend the pattern classes.

7. Let's Begin
In our example, we are going to pretend you want to
integrate a function with social media. So lets start by
making two social media classes. Keep note that in our
example, one of our classes has a static method.
The argument passed from the method observed

8. Messenger Object
Now we are going create a class that has the ability to
send messages to objects that are observing this method.
Extends PVObject
Implements the ability to call observers
The name of the event that observrs look for Value passed to objects that are observing

9. Take Notice!
1. Our class extends PVObject. PVObject extends
PVPatterns which has our methods needed to use the
observer. The method that will notify other methods
than an action has occurred is _notify().
2. The method notify has the parameter 'new_message'.
This is the name of the event that is going to cause the
notifications. After the event name, we can add as many
parameters as we want but in this example we are only
adding one, the message.

10. Round 1
The first test we are going to do is just sending a message
without adding an observer. So lets initialize the object
and send a message.

11. Result
The result here will be very simple.

12. Round 2
Now lets attach our observers. At minimum, the observer
requires 3 arguments. The first argument is the name of the
event. Our event name has to match to event name set in
the notifier, which is 'new_message'. The second argument
is the class to be called and the third is the method in the
class to be called when the event is executed The last is
options, namely for if our method is not static, apply the
'instance’ option here.
Code example on next slide =>

13. Attach the Observers
Call an instance of
Event Name Class to call Method in class to call an object
Event Name Class to call Method in class to call

14. And the output….

15. Challenge!
Below is an optional challenge to perform that is designed to help you
gain a better understanding of the design pattern.
1. Look through ProdigyView’s source code and find the PVSession
class.
2. Find the event name for either writing a session or writing a
cookie.
3. Create a class that accepts the same parameters that the method
in the Session class outputs.
4. Add that class as an observer to PVSession:writeCookie() or
PVSession::writeMethod
5. Execute PVSession:writeCookie() or PVSession::writeMethod
and print out the results in the class you created.

16. Summary
1. Add _notify to a function and set the event name. Add
as many parameters as you need after the event name.
Parameters will be passed to the functions that’s are
listening.
2. Attach an observer with _addObserver. Make sure to
specify the name of the event, the class and method the
even will be calling.

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