Events

1. Events Chapter 7

2. Interactive • The real world is interactive • User determines order of actions instead of programmer

3. Control of Flow • How sequence of actions in program is controlled • What action happens first, next, and so on • Animations • Movie-style - programmer determines sequence of actions prior program running • Interactive - sequence of actions determined at runtime by user

4. Event • Program reacts to • Mouse click • Key press on keyboard • Changes that occur during program execution • Control of flow is now controlled by user

5. Events • Each time user provides some sort of input, we say an eventis generated • An event is “something that happens” • An event may • Trigger a response • Move objects into positions that create a condition that triggers a response • Ex: A collision that moves objects

6. Event Handler Method • Called when event occurs • Also called behavior • Linked to event in Event editor • Behavior – when method linked to event is performed due to an action

7. Creating An Event Click on create new event in Events window

8. 6.1 Alice Events • When the world starts • When a key is typed • When the mouse is clicked on something • While something is true • When a variable changes • Let the mouse move <object> • Let the arrow keys move <subject> • let the mouse move the camera • Let the mouse orient the camera • See Table 7-1 on page 272 for details of each

9. 6.1 Specialized Events • Some events from the previous list do not appear in the Events Editor • While a key is typed (When a key is typed) • While the mouse is pressed on something (When mouse clicked on) • While the world is running (when world starts) • When something becomes true (While something becomes true) • To create specialized event • Create general event in parenthesis above • Right-click and select change to action on left above

10. 6.2 Key Typed Event • Alice can detect when a key on keyboard is pressed • Event is triggered when the user types a key • Keyboard key that triggers event must be specified • any key is the placeholder until you choose a specific key • Can have event activated when any key is pressed • Click on Nothing • Choose custom method from drop down menu

11. Tutorial 7-1: Key Press Event • Have each fairy flap her wings and move up and down when a key is pressed called fly • When G is pressed event to cause Gossamer to fly • When M is pressed event to cause Hazelnut to fly

12. Storyboards Event: G key is pressed Response: Do together Flap wings of Gossamer Move Gossamer up ½ meter Do together Flap wings of Gossamer Move Gossamer down ½ meter Event: M key is pressed Response: Do together Flap wings of Hazelnut Move Hazelnut up ½ meter Do together Flap wings of Hazelnut Move Hazelnut down ½ meter

13. Programs for Faeries Flying Both events can run at same time

14. Mouse Event • Interactive programs often allow the user to use a mouse to click • Examples • Buttons in a windows-based interface • Choose targets in a game • Select items on a form checklist

15. 6.2 Creating Mouse Event • Event is triggered when the mouse is clicked on an object in the world • Click on create new event and choose When the mouse is clicked on something • It can be • Anything • Any object in the Alice World • Choose event handler by clicking on nothing

16. Tutorial 7-3: Mouse Event • Click on refrigerator door causes door to open • Can place Alice statement directly in event declaration

17. Fridge Door Opens and Closes • To get door to open and close you need to remember the state of the door • Is it open or closed? • Use boolean variable: doorOpen • If doorOpen = true then door is open • Close door • Set doorOpen to false • If doorOpen = false then door is closed • Open door • Set doorOpen to true

18. Storyboard Event: Mouse clicked on fridge door Response: If doorOpen = true Turn door right ¼ revolution doorOpen = false Else Turn door left ¼ revolution doorOpen = true

19. Program to Open and Close Door

20. Create Your Own People Models • Use hebuilder and shebuilder • In People gallery • Choose all features of person • Has built-in methods • hello, angry, happy, walk, confused, no, yes

21. Homework • Read chapter 6 sections 1 and 2 • Answer questions in handout • Do lab assignments after handing in answered questions • Due one week after assigned with 1 week grace