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Events Chapter 7. Interactive Real world is interactive User determines order of actions instead of programmer.

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Presentation on theme: "Events Chapter 7. Interactive Real world is interactive User determines order of actions instead of programmer."— Presentation transcript:

1 Events Chapter 7

2 Interactive Real world is interactive User determines order of actions instead of programmer

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

4 Event Program reacts to o Mouse click o Key press on keyboard o 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 event is generated o An event is “something that happens” An event may o Trigger a response o 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 o 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 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 Let the arrow keys move let the mouse move the camera Let the mouse orient the camera See Table 7-1 on page 272 for details of each

9 Specialized Events Some events from the previous list do not appear in the Events Editor o While a key is pressed o While the mouse is pressed on something o While the world is running o When something becomes true To create specialized event o Create general event o Right-click and select change to

10 Key Press Event Alice can detect when a key on keyboard is pressed o Event is triggered when the user types a key o Key that will trigger the event must be specified o any key is the placeholder until you choose a specific key  Can have event activated when any key is pressed o 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 o When G is pressed event to cause Gossamer to fly o When M is pressed event to cause Hazelnut to fly 6-11

12 Storyboards 6-12 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 o Buttons in a windows-based interface o Choose targets in a game o Select items in checklist on a form 6-14

15 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 o Anything o 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 o Can place Alice statement directly in event declaration 6-16

17 Fridge Door Opens and Closes To get door to open and close you need to remember the state of the door o Is it open or closed? o Use boolean variable: doorOpen If doorOpen = true then door is open o Close door o Set doorOpen to false If doorOpen = false then door is closed o Open door o Set doorOpen to true 6-17

18 Storyboard 6-18 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 o In People gallery o Choose all features of person o 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


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