| 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 | 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 | 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 | 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 | 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 | |
