1. Ch 9 Lists
In some animations, several objects must perform the same actions
Example:
A marching band, where the band members are performing the same marching steps.
In such situations, it is convenient to collect all the objects into a list – a group or collection of objects
Fall 2008
ACS Ron McFadyen

2. Lists With Alice, we can organize objects into a list.
In our daily lives, we use lists to help us organize things. For example,
to-do list
assignments
shopping
In programming, a list is a special kind of data structure.
Fall 2008
ACS Ron McFadyen

3. Types of Lists
In Alice, a list can be a list of numbers or a list of objects, colors, or other type ….
Fall 2008
ACS Ron McFadyen

4. Example
The famous Rockettes® are preparing for their winter holiday show. You have been hired to create an animation for the holiday show that will be used on a web site where people can purchase tickets for the show.
Fall 2008
ACS Ron McFadyen

5. Creating the list
Create the initial world and add five rockette objects to the world.
Create a new world-level variable in the properties panel.
Fall 2008
ACS Ron McFadyen

6. Creating the list In the popup dialog box, type in a name
select Object type
check “make a List” box
click new item button 5
times to select each
of the 5 rockettes,
one at a time
Fall 2008
ACS Ron McFadyen

7. Programming with lists
One of the most useful operations with a list is to repeatedly perform some action with each item in the list.
This is called iteration or "iterating through a list."
Fall 2008
ACS Ron McFadyen

8. Iterating through a list
Two control structures for iterating through a list:
in order (one at a time)
all together (simultaneously)
Fall 2008
ACS Ron McFadyen

9. Example: Iteration in Order
A typical chorus line dance involves each dancer (one after the other) kicking up a leg.
Possible storyboard:
kickUpRightLeg
Parameter: whichRockette
Do in order
Do together
whichRockette right thigh turn back
whichRockette right calf turn forward
whichRockette right calf turn back
For all dancers in order
item_from_dancers kickUpRightLeg
Implementing in Alice ….
Fall 2008
ACS Ron McFadyen

10. Example: Iteration all together
A typical chorus line dance involves each dancer (one after the other) kicking up a leg.
Possible storyboard:
kickUpRightLeg
Parameter: whichRockette
Do in order
Do together
whichRockette right thigh turn back
whichRockette right calf turn forward
whichRockette right calf turn back
For all dancers simultaneously
item_from_dancers kickUpRightLeg
Implementing in Alice ….
Fall 2008
ACS Ron McFadyen

11. Common Uses of Lists
Iterating through a list of several like items to accomplish the same task with each item.
As in the previous Rockettes example
Iterating through a list of several like items to search for an item with a given property...
Fall 2008
ACS Ron McFadyen

12. Example A WacAMole arcade game.
Little moles pop up from holes in the top of the booth. The user tries to whack the mole before it drops out of sight.
The game is over when 10 moles are whacked.
Fall 2008
ACS Ron McFadyen

13. Designing the game
To design the game animation, we need to answer several questions:
How will the game work, overall?
How do we keep score?
How do we know when the user whacks a
mole?
How will a list help us?
Fall 2008
ACS Ron McFadyen

14. How will the game work?
A mole pops up and then goes back down. Each time the mole pops up, the user attempts to use the mouse to click the mole.
When a click occurs, we check to see if a mole was clicked. If so, a sound plays and the score increases.
The above actions repeat until the game is over.
Fall 2008
ACS Ron McFadyen

15. Overall design See next slide Is the game over? yes congratulate no
pop random mole
Mouse click event
See next slide
Fall 2008
ACS Ron McFadyen

16. Overall design Mouse click event yes Did mouse click on a mole?
Play sound
Change score display no
do nothing
Fall 2008
ACS Ron McFadyen

17. Storyboard for overall game
This is the main driver for the game.
The code will be written in World.my first method
While the game isn't over
randomly select one mole and call popMole
Congratulate the user
Fall 2008
ACS Ron McFadyen

18. Storyboard: popMole popMole Do in order Move the mole up
Wait some time
Move the mole back down
Fall 2008
ACS Ron McFadyen

19. Keeping Score We will use a visual scorekeeper.
The scorekeeper is made up of two cylinders
A gray cylinder above the ground
A yellow cylinder below the ground.
Each cylinder is 1 meter in height.
Fall 2008
ACS Ron McFadyen

20. Keeping score
Each time the user successfully clicks a mole, the yellow cylinder will move up 1/10 meter.
When the yellow cylinder is above ground (has moved up 10 times), the game is over.
Fall 2008
ACS Ron McFadyen

21. When a mole is clicked This is where a list comes in handy:
create a list of the moles (one mole is below each hole)
create a mouse click event
each time the mouse is clicked, call a score method to iterate through the list of moles to see whether one of the moles has been clicked!
Fall 2008
ACS Ron McFadyen

22. Storyboard: keep score
Event: User clicks mouse
Response: score
For All in order
If any mole in the mole list was the object clicked
Make a noise
Move the playerscore (yellow cylinder) up 1/10 meter
And implementing in Alice …
Fall 2008
ACS Ron McFadyen