Alice 2.0

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Alice 2.0

• Introduction to Event-Driven Programming
• Mr. Planck

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Show Respect

• Value yourself. Be honest and ethical, and
  practice strong moral values.
• Treat all members of the school community and all
  visitors with politeness and respect.
• Honor the ideas and opinions of others.
• Offer to help.
• Be responsible with property and belongings.
• FOLLOW THE LEADER!

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• The driver of a car is responsible for deciding
  what operations the car will perform. Without a
  driver the car will just wait for the driver to
  tell it what to do next. Looking at this picture
  what are some of the things a driver can tell a
  car to do?

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Driving a Car
Tell (trigger) wait (listen) do (handle)
Press Accelerator Increase speed
Press Brake Pedal Decrease speed
Turn steering wheel right Turn front wheels right
Move stick shift to D Enable car to move forward
Move stick shift to R Enable car to move backward
Turn radio volume clockwise Increase radio volume
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Using a Word Processor

• What about a computer program like Microsoft
  Word?

Even Trigger (tell) Event Listener (wait) Event Handler (do)
Press B Type the letter b in the doc
Press the left mouse button Set the typing cursor in the doc
Alt F Open the File menu

• The event trigger is typically caused by a
  computer user manipulating some hardware
  (keyboard, mouse, scanner, etc.) but can be
  anything (date/time, email address, etc.)

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What is Event-driven programming?

• In conventional programming, the sequence of
  operations for an application is determined by a
  central controlling program (e.g., a main
  procedure). In event-driven programming, the
  sequence of operations for an application is
  determined by the users interaction with the
  applications interface (forms, menus, buttons,
  etc.).
• To create an event-driven application, the
  programmer creates small programscalled event
  handlersand associates them with specific events
  raised by specific objects.
• Most, if not all, GUI systems are designed to be
  event driven, meaning that the main flow of your
  program is not sequential from beginning to end.
  If you've never done GUI programming, this is one
  of the trickiest paradigm shifts.
• The Hollywood Principle "Don't call us we'll
  call you." ... You implement the event handlers,
  you get registered. You get called when the time
  is right (event trigger). This requires a
  distinctly different way of thinking to that
  which is taught in introductory programming where
  the student dictates the flow of control.

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Event-driven programming

• The use of a GUI on a computer system requires
  event-driven programming. An event occurs
  whenever an event listener detects an event
  trigger and responds by running a method called
  an event handler. An event listener is a
  combination of hardware and software that
  repeatedly checks the computer system for the
  event trigger.
• An event trigger can be any activity or condition
  selected by the programmer, such as someone
  pressing the Enter key or a bank account balance
  going below zero.
• An event handler is a method that is activated
  when the trigger occurs. Almost any method can
  serve as an event handler.

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Extended Activity

• Add three more events to your current ballerina
  world (keep the ones we created together, just
  add these additional ones)
• Add an event trigger based on the up arrow key on
  the keyboard that will move the pinkBallerina up
  ½ meter
• Add an event trigger based on the down arrow key
  on the keyboard that will move the pinkBallerina
  down ½ meter
• Add and event trigger based on clicking the mouse
  on the pinkBallerina that will make her say
  Ouch!

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Extended Activity

• Once these new events are working properly print
  your work using the menu File-gtExport code for
  printing
• A dialog box will appear, you must enter your
  name for the Authors name and the press the
  Export Code button (you will have many more
  directions to export than seen in the example
  below).

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Extended Activity

• Find the newly exported html file with your Alice
  code on the desktop and print it to hand in at
  the end of class.
• Download Alice at http//www.alice.org/ to use on
  your home computer