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12.12 The Multiple-Choice Quiz, OOP Style

Now that you understand the principles of OOP, let's return to our multiple-choice quiz example to see them in action. The source code for our OOP quiz is too long to present here, but it can be downloaded from the Code Depot. The important part of the application is its object design, listed next. Even without seeing the code in the quiz, the following tables—which describe the classes, methods, properties, and events in the quiz—should give you a complete picture of how the application works. In fact, using the following structure, you may want to try to build the quiz yourself before you download its source code. Note that some properties are not listed in the tables, because they are used by a class's methods only, and they are therefore considered internal ("private") to the class.

Our quiz comprises three classes, shown in Table 12-2. The entire quiz is generated from ActionScript—there's not a single asset in the movie's Library. All buttons are drawn with the Drawing API, and all text is created with MovieClip.createTextField( ), giving the quiz a flexible layout that adapts to the current Player size, question length, and answer length. Navigation buttons—Next, Back, Grade, and Try Again—let the user proceed nonlinearly through the quiz, change an existing answer, be graded, or retry the quiz.

Table 12-2. Multiple-choice quiz classes

Class name	Class description
Quiz	Manages the data (questions and answers) in the quiz Handles loading questions from an external XML file Starts the quiz and tracks the current question Grades the user
QuizGUI	Displays the quiz on screen and receives user input
Question	Manages the data of an individual question and its answer

The Quiz class defines the methods and properties listed in Table 12-3.

Table 12-3. The Quiz class

Name	Type	Description
loadQuizData( )	Method	Loads an XML file and generates the quiz based on it
startNewQuiz( )	Method	Resets the quiz and tells the QuizGUI it's time to begin the quiz
setQuizGUI	Method	Stores a reference to a QuizGUI instance that will represent the quiz on screen
setTitle( )	Method	Stores the quiz title
getTitle( )	Method	Returns the quiz title
setDescription( )	Method	Stores a short text description for the quiz
getDescription( )	Method	Returns the quiz description
getScore( )	Method	Calculates and returns the user's current score, based on the questions answered so far
setCurrentQuestion( )	Method	Sets the question being answered
getCurrentQuestion( )	Method	Returns the index of the question currently being answered
getNumUserAnswers( )	Method	Returns the number of questions answered so far
setNumUserAnswers( )	Method	Sets the number of questions answered so far
setUserAnswer( )	Method	Stores the user's answer for a specific question
addQuestion( )	Method	Inserts a new Question object into the quiz
getQuestionAt( )	Method	Returns a specific Question object from the list of questions in the quiz
getNumQuestions( )	Method	Returns the number of questions in the quiz
isComplete( )	Method	Returns true if the quiz is considered finished; otherwise it returns false. In the simplest case, a quiz is complete when all the questions have been answered by the user.
quizGUI	Property	A reference to the QuizGUI instance that will display the quiz

The QuizGUI class defines the methods, properties, and events listed in Table 12-4. Note that the event handlers on the QuizGUI class should more appropriately be defined as Quiz listener events. However, because ActionScript does not provide a built-in means of creating listener events, we keep the code simple by placing the handlers directly on QuizGUI.

Table 12-4. The QuizGUI class

Name	Type	Description
displaySplashScreen( )	Method	Displays a welcome screen for the quiz
displayQuestion( )	Method	Displays an entire question, including answer and navigation buttons
displayQuizEnd( )	Method	Displays a final status report for the quiz, showing the user's score
displayTitle( )	Method	Displays the quiz title on screen
createNavButton( )	Method	A convenience function that creates and returns a navigation button
clearScreen( )	Method	Removes all visual assets from the screen
onQuizStart( )	Event Handler	Invoked when a new quiz begins
onQuestionUpdate( )	Event Handler	Invoked when the content of a question changes, the user submits an answer, or the current question index changes
onQuizComplete( )	Event Handler	Invoked when the user has answered every question
quizObj	Property	A reference to the Quiz instance for which this QuizGUI is handling display
quizClip	Property	A reference to the movie clip in which the quiz display assets will be created

The Question class defines the methods listed in Table 12-5. The Question constructor can receive question data either as a series of values or as a single XML fragment.

Table 12-5. The Question class

Name	Type	Description
setQuestionText( )	Method	Assigns the text for the question
getQuestionText( )	Method	Returns the text for the question
setAnswers( )	Method	Assigns the multiple-choice answers, as an array
getAnswers( )	Method	Returns the multiple-choice answers, as an array
setCorrectAnswer( )	Method	Assigns the correct answer for the question, as an index in the answers array
getCorrectAnswer( )	Method	Returns the correct answer for the question, as an index in the answers array
setUserAnswer( )	Method	Assigns the user's answer for the question, as an index in the answers array. This can be set more than once.
getUserAnswer( )	Method	Returns the user's current answer for the question, as an index in the answers array

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