Lesson 5:

Events

Introduction

Try this activity to show events: Have Student A go out, ask him to close the door behind him, wait a few seconds, and then knock on the door (preferably, you want to do this without the rest of the class noticing). Another student is likely to hear the knock and open the door. If no one opens the door, you can ask someone to do so. Tell the students that knocking on the door is an event and the reaction to that event was opening the door. Ask them for other examples of events in their daily life.

Let’s think about some examples of events in our daily life

When there’s a red light, cars stop

You feel hungry so you eat

Stubbing your toe and yelling “Ouch!”

Getting the basketball in the basket and scoring a point for your team!

You click on a Youtube video so it plays

What is an Event?

Click below to watch a video

Play Video Event

Event.- An action that causes something to happen.

pencilcode.net

Review about the comments in pencilcode.net

What is a comment in Programming?

Comments are used to document your code so it is easier for humans to understand. You should include a comment any time you think there is something that needs an explanation. Especially if you are part of a team, another programmer can more easily maintain or modify the code in the future.

Place symbol # at the beginning of the coding line to comment in CoffeeScript

Create events for the arrow keys

Have them identify the arrow keys of the keyboard

Notice that every time you hit a key is an event and we need to write the code for the action to be taken by the computer.

New File: events

show them how to get the block “keydown” from the Control section for the “up arrow” key, then let them get the block to move forward. Write the comments.

Let them figure out how to create the event for the “down arrow” key.

Repeat the process to the right and left turn

speed 10

#EVENT: Press “up arrow” key

#ACTION: Turtle moves 10 steps forward

keydown ‘up’, ->

fd 10

#EVENT: Press “down arrow” key

#ACTION: Turtle moves 10 steps backwards

keydown ‘down’, ->

bk 10

#EVENT: Press “right arrow” key

#ACTION: Turtle turns right

keydown ‘right’, ->

rt 90

#EVENT: Press “left arrow” key

#ACTION: Turtle turns left

keydown ‘left’, ->

lt 90

NOTICE: When you run the program the turtle won’t move unless you press one of the arrow keys.

Challenge

Add a color to each keydown when our turtle moves forward and back.

Wrap Up

What is an event?

Why do we need to be able to handle events in a program?

What are some other kinds of events that you can think of?