Fall 2007ACS-1805 Ron McFadyen1 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 2007ACS-1805 Ron McFadyen2 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 2007ACS-1805 Ron McFadyen3 Types of Lists In Alice, a list can be a list of numbers or a list of objects, colors, or other type ….

Fall 2007ACS-1805 Ron McFadyen4 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 2007ACS-1805 Ron McFadyen5 Creating the list Create the initial world and add five rockette objects to the world. Then, create a new world-level variable in the properties panel. (Why should it be world-level?)

Fall 2007ACS-1805 Ron McFadyen6 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 2007ACS-1805 Ron McFadyen7 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 2007ACS-1805 Ron McFadyen8 Iterating through a list Two control structures for iterating through a list: in order (one at a time) all together (simultaneously)

Fall 2007ACS-1805 Ron McFadyen9 Example: Iteration in Order A typical chorus line dance involves each dancer (one after the other) kicking up a leg. Possible storyboard: For all dancers in order item_from_dancers kickUpRightLeg kickUpRightLeg Parameter: whichRockette Do in order Do together whichRockette right thigh turn back whichRockette right calf turn forward whichRockette right calf turn back Implementing in Alice ….

Fall 2007ACS-1805 Ron McFadyen10 Example: Iteration all together A typical chorus line dance involves each dancer (one after the other) kicking up a leg. Possible storyboard: For all dancers simultaneously item_from_dancers kickUpRightLeg kickUpRightLeg Parameter: whichRockette Do in order Do together whichRockette right thigh turn back whichRockette right calf turn forward whichRockette right calf turn back Implementing in Alice ….

Fall 2007ACS-1805 Ron McFadyen11 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 2007ACS-1805 Ron McFadyen12 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 2007ACS-1805 Ron McFadyen13 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 2007ACS-1805 Ron McFadyen14 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 2007ACS-1805 Ron McFadyen15 Is the game over? Overall design pop random mole no yes congratulate Mouse click event See next slide

Fall 2007ACS-1805 Ron McFadyen16 Overall design Did mouse click on a mole? yes Play sound Change score display Mouse click event no do nothing

Fall 2007ACS-1805 Ron McFadyen17 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 2007ACS-1805 Ron McFadyen18 Storyboard: popMole popMole Do in order Move the mole up Wait some time Move the mole back down

Fall 2007ACS-1805 Ron McFadyen19 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 2007ACS-1805 Ron McFadyen20 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 2007ACS-1805 Ron McFadyen21 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 2007ACS-1805 Ron McFadyen22 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 …