Event Driven Programming

1
Event Driven Programming

• Chapter 5

2
Sequential Programming

• Computer-Centric
• Program Runs as Programmer Intended
• Programmer Sets the Order of Action
• Programmer Controls the Programs Flow

3
Event Driven Programming

• User-Centric
• Computer User Determines the Order of Actions
• Programs are Interactive
• Flow of Control is Determined at Runtime
• User Clicks Mouse / Presses Key
• Object in Scene Moves to create a Condition

4
Event

• Something that happens
• Can be caused by computer or user
• Mouse Click
• Key Press
• System Clock Tick
• Can occur differently each time the program is
  executed
• Events are WORLD Level

5
Event Handling

• Response to an event
• Action or Sequence of Actions carried out when
  Event Occurs (Methods)
• Events TRIGGER response
• Programmer must think of all possible events
• Plan a Response for Each (Event Handler)

6
Linking

• Event Handling Methods must be linked to the
  Specific Event
• Event Occurs which causes the Event Handling
  Method to execute

7
Testing

• Testing of Event Driven Programs is much more
  difficult
• Programmer does not know flow of program
• Flow of Program changes every time program is
  executed
• Users Actions are difficult to pre-determine
• Use Incremental Development and Testing
• Write a Method
• Test it
• Write a Method
• Test it
• Etc.

8
Example Program

• Create a Whack A Mole program. Use the
  whackAmoleBooth object from the amusement park
  gallery.
• Pressing the M key makes the mole pop up
• Clicking the mouse on the mole makes the bopper
  try to hit the mole

9
Design Storyboards

• Event Key Press Letter M
• Response
• Make mole lift out of booth
• Mole says Get me if you can!
• Make mole go back into booth

10
Design Storyboard

• Event Mouse Click on Mole Object
• Response
• Lift Bopper off Booth
• Move Bopper to Booth towards Mole
• Lift Bopper off Booth

11
Create Methods

• World Level or Class Level Methods?
• Why
• Create moleAppear method

12
Linking Event to Method

• Create New Event
• When a Key is Typed

13
Linking Events to Methods

• Select Specific Key
• M ? Make Mole Appear

14
Link Event to Method

• Select Method to Link
• wackAmoleBooth, moleAppears
• TEST

15
Create Method

• Create bopMole method
• Link to Mouse Click on Mole Event
• Test

16
Run the Program

• Try to Whack The Mole
• Click M to make moleAppear Event Handling
  Method execute
• Mouse Click on Mole to make bopMole Event
  Handling Method execute

17
Homework

• Chapter 5
• 5-1 Exercises
• 1 ? Flight Simulator
• 4 ? Typing Tutor

18
Events with Parameters

• Remember Parameters are how we send information
  to the methods
• Customize Methods for different objects/values

19
Create Scenes/Methods

• Example (Textbook page 125)
• A firetruck has been called to an emergency in a
  burning building. A person and a fire object has
  been placed on each floor. When each person is
  selected, the truck will need to extend its
  ladder so that each person can climb down to
  safety.

20
Design

• Event 1 Click on 1st person
• Responding Method Save person on 1st floor
• Event 2 Click on 2nd person
• Responding Method Save person on 2nd floor
• Event 3 Click on 3rd person
• Responding Method Save person on 3rd floor

21
Design 2

• Events Click on Person
• Responding Method SavePerson
• Point the ladder at the correct floor (parameter
  Which floor)
• Extend the ladder correct amount (parameter How
  far)
• Specific person (parameter Which person) slides
  down ladder to the firetruck
• Pull the ladder back in correct amount (parameter
  How far)

22
Create Scene

• Burning Building (building)
• Firetruck (vehicles)
• 3 People use whichever you want
• RandomGirl1
• RandomGirl2
• RandomGuy2
• FireAnim www.alice.org
• Gallery
• Save As name.a2c (not ZIP file)
• Put in correct Alice gallery folder
• Alice\Alice\Required\Gallery\

23
Create Method as Before

• World Method or Class Method?
• Parameters
• whichFloor (object)
• whichPerson (object)
• howFar (number)

24
SavePerson Method
25
Link Method to Event
26
Test the Program

• Run the program
• VERY Important when using parameters
• Run several times
• Number Parameters
• Small Number
• Large Number
• Negative Number

27
Complex Problems

• Responses to events may involve multiple actions
• Methods can call other methods
• Parameters can be used when methods call methods

28
Homework

• 5-2
• Problems 12 14