Which Of The Following Is Not True About The Use Of Apps?

QuizMe is a trivia game about baseball, but you can use it as a template to build quizzes on any topic. With QuizMe:

The user steps through a series of questions, clicking a button to proceed to the next question.
The user enters an answer for each question and the app reports whether each answer is correct or not.

With QuizMe, the quiz questions are always the same unless you, the programmer, change them. Later, you can create MakeQuiz & TakeQuiz, an app that lets users of the app create and modify the quiz questions.

This tutorial assumes you are familiar with the basics of App Inventor -- using the Component Designer to build a user interface, and using the Blocks Editor to specify event-handlers. If you are not familiar with the basics, try stepping through some of the basic tutorials before continuing.

Connect to the App Inventor web site and start a new project. Name it QuizMe, and also set the screen's Title to "QuizMe". Open the Blocks Editor and connect to the phone.

Also download the following pictures of baseball players and save them on your computer. Later, you'll load these images into your project.

Larsenberra.jpg
Dallasbraden.jpg
Cyyoung.jpg
Nolanryan.jpg

You'll design the quiz game so that the user proceeds from question to question by clicking a Next button, and receives simple correct/incorrect feedback on each answer.

This tutorial introduces:

Defining and displaying lists of information.
Sequencing through a list using an index variable -- a variable that keeps track of a position in a list.
Conditional behaviors-- performing certain operations only when a condition is met.
Switching an image to show a different picture at different times.

Use the component designer to create the interface for QuizMe. When you finish, it should look something like the snapshot below (there are also more detailed instructions below the snapshot).

To create this interface, first load the images you downloaded into the project. Click on the "Upload File..." button in the Media area and select one of the downloaded files (e.g., Larsenberra.jpg). Then do the same for the other three images.

Next, create the following components by dragging them from the Palette into the Viewer and et the properties of the components as described below:

Component Type	Palette Group	What you'll name it	Action	Purpose of Component
Image	User Interface	Image1	Set its Picture property to "Larsenberra.jpg". This is the first picture that should appear.	The picture part of the question
Label	User Interface	QuestionLabel	Change Text property to "Question:"	Displays the current question
HorizontalArrangement	Layout	HorizontalArrangement1		Organizes the AnswerPrompt and Text
Label	User Interface	AnswerPromptLabel	Change Text property to "Enter Answer:". On the Viewer screen, move this label into HorizontalArrangement1.	Text prompting for an anwer
TextBox	User Interface	AnswerText	Change Hint to "Please Enter an Answer". On the Viewer screen, move AnswerText into HorizontalArrangement1.	User will enter answer here.
Label	User Interface	RightWrongLabel	Change Text property to "Correct/Incorrect".	Correct/Incorrect is displayed here.
HorizontalArrangement	Layout	HorizontalArrangement2		Organizes the AnswerButton and NextButton
Button	User Interface	AnswerButton	Change Text property to "Submit". On the Viewer, move the button into HorizontalArrangment2.	User clicks to submit an answer
Button	User Interface	NextButton	Change Text property to "Next". Move the button into HorizontalArrangement2.	User clicks to proceed to the next answer

Open the Blocks Editor to add the behaviors for the app. First, you'll define two list variables, QuestionList to hold the list of questions, and AnswerList to hold the list of corresponding answers.

To define the two list variables, you'll need the following blocks:

Block Type	Drawer	Purpose
initialize global name to	Variables	Defines the QuestionList variable (rename it)
initialize global name to	Variables	Defines the AnswerList variable (rename it)
make a list	Lists	Used to insert the items of the QuestionList
" " (3 of them)	Text	The actual questions
make a list	Lists	Used to insert the items of the AnswerList
" " (3 of them)	Text	The actual answers

You create global variables by dragging in a initialize global name to block from the Variables drawer and double-clicking the default name "name" to change its name. The initialize global name to block has a slot for the initial value of the variable. The variable can represent a number or text, or even a list, for which you can plug in a make a list block into the variable definition.

The blocks should look like this:

Each time the user clicks the NextButton to proceed through the quiz, the app needs to remember which question it is on. In programming, to remember something, you define a new variable. In this case, the app needs to remember the current question number -- the index into the list QuestionList.

To create the variable currentQuestionIndex, you'll need the following blocks:

Block Type	Drawer	Purpose
initialize global name to	Variables	Defines the currentQuestionIndex variable (rename it)
0 (1)	Math	Set the initial value of currentQuestionIndex to 1 (renumber it)

The blocks should look like this:

To start, you'll ignore the answers and just work on the behavior to sequence through the questions. The desired behavior is the following: when the app starts, the first question should appear in the label named QuestionLabel. When the user clicks the NextButton, the second question should appear. When the user clicks again, the third should appear. When the last question is reached, clicking the NextButton should result in the first question once again appearing in the QuestionLabel.

With App Inventor, you select particular items in a list with the select list item block. The block asks you to specify the list and an index--a position in the list. If a list has three items, the indexes 1, 2, and 3 are valid.

For QuizMe, when the app starts, the app should choose the first question in the list and display it in the QuestionLabel component.

For this app initialization behavior, you'll need the following blocks:

Block Type	Drawer	Purpose
when Screen1.Initialize	Screen1	When the app begins, this event-handler is triggered.
set QuestionLabel.Text to	QuestionLabel	Need to put the first question in QuestionLabel
select list item	Lists	Need to select the first question from QuestionLabel
get	Variables	The list to select from. Select "global QuestionList"
0 (1)	Math	Select the first question by using an index of 1. Set the value to be 1.

The blocks should look like this:

The when Screen1.Initialize event is triggered when the app begins. The first item of the variable QuestionList is selected and placed into set QuestionLabel.Text. So when the app begins, the user will see the first question.

Test this behavior. Click Connect Phone if your phone is not already connected. What appears on the phone? If you created the QuestionList as described above, the first item of QuestionList, "Who pitched a perfect game in the World Series?", should appear in the QuestionLabel.

Now program the behavior of the NextButton. You've already defined the currentQuestionIndex to remember the question the user is on. When NextButton is clicked, the app needs to increment this variable, e.g., change it from 1 to 2 or from 2 to 3, etc., and then use the resulting value to select the new "current" question. For this behavior, you'll need the following blocks:

Block Type	Drawer	Purpose
when NextButton.Click	NextButton	When user clicks Next, this event-handler is triggered.
set currentQuestionIndex to	Variables	Need to put the first question in QuestionLabel
+	Math	Used to increment currentQuestionIndex
get global currentQuestionIndex	Variables	New value will be old value + 1
0 (1)	Math	For the + 1
set QuestionLabel.Text to	QuestionLabel	Need to display the next question here
select list item	Lists	Need to select the first question from QuestionList
get global QuestionList	Variables	Plug into list slot of call select list item
get global currentQuestionIndex	Variables	Plug into index slot of call select list item, we want nth item

The blocks should look like this:

The first row of blocks increments the variable currentQuestionIndex. If currentQuestionIndex has a 1 in it, it is changed to 2. If it has a 2, it is changed to 3, and so on. Once the currentQuestionIndex variable has been changed, the app uses it to select the "current" question.

Recall that in the Screen.Initialize event-handler, the app selected the first question to display:

When the NextButton is clicked, the app doesn't choose the first item in the list, or the 2nd or 3rd, it chooses the currentQuestionIndex-th item.

The blocks are executed in a right-to-left manner. The app first evaluates the index parameter of select list item, which is the variable currentQuestionIndex. The number is stored in currentQuestionIndex is used as the index when the select list item is executed.

When the NextButton is clicked for the first time, the increment blocks will set currentQuestionIndex from 1 to 2, so the app will select the second item from QuestionList, "who pitched the first perfect game of 2010?". The second time NextButton is clicked, currentQuestionIndex will be set from 2 to 3, and the app will select the 3rd question in the list, "who pitched the first perfect game of the modern era?"

Test this behavior. Test the behavior of the NextButton to see if the app is working correctly thus far. To test, play the role of the user and click the NextButton on the phone. Does the phone display the second question, "Who pitched the first perfect game of 2010?" It should, and the third question should appear when you click the NextButton again. If this is working, pat yourself on the back quickly, and then go on.

Try clicking the NextButton again (a third time). You should see an error: "Attempting to get item 4 of a list of length 3". The app has a bug-- do you know what the problem is?

The problem with the app is that it always increments the currentQuestionIndex variable when the NextButton is clicked. When currentQuestionIndex is already 3 and the user clicks the NextButton, the app changes currentQuestionIndex from 3 to 4, then calls select list item to get the currentQuestionIndex-th , or in this case, the 4th item. Since there are only three items in the variable QuestionList, Android complains.

What the app needs to do is ask a question-- check a condition-- when the NextButton is clicked, and execute different blocks dependending on the answer. One way to ask the question is to ask, "is the variable currentQuestionIndex already 3?" If the answer is yes, you should set currentQuestionIndex back to 0 so the user is taken back to the first question.

You'll need the following blocks:

Block Type	Drawer	Purpose
if then	Control	To ask if user is on last question
=	Math	to test if currentQuestionIndex is 3
get global currentQuestionIndex	Variables	-
0 (3)	Math	3 is number of items in the list
set currentQuestionIndex to	Variables	set to 0 to go back to first question
0	Math	set to 0 because next blocks will increment to 1

The modified when NextButton.Click event-handler should look like this:

When the NextButton is clicked, the app first checks to see if currentQuestionIndex has a 3 in it. If it does, currentQuestionIndex is set back to 0 so that when 1 is added to it with the blocks below, it will be 1 and the quiz will loop back to display the first question. Note that only the blocks inset within the if-then block are dependent on the condition-- the increment and set set QuestionLabel.Text to blocks are executed under all conditions.

Next, you'll modify the app to make it easy to add and remove elements from the list. You'll rewrite the blocks so that they'll work on any list, not just one with exactly three items. To begin, add a fourth question to QuestionList and another answer into AnswerList. To do this, you will first need to expand the number of available slots by using the mutator. For more information on how to use the mutator, click here. The blocks should look like this:

Test the modified app. Click the NextButton a number of times. You should see that the fourth question never appears, no matter how many times you click Next.

The problem is that the test to see if the user is on the last question is too specific: it asks if the currentQuestionIndex variable is 3:

You could just change the number 3 to a 4, and the app would again work correctly. The problem with this solution, however, is that each time you modify the questions and answers, you also have to remember to make this change. Such dependencies in a computer program often lead to bugs, especially as an app grows in complexity. It's much better to set the program up so that it will work no matter how many questions there are. Such generality is even more important when the list you are working with changes dynamically, e.g., a quiz app that allows the user to add new questions.

The better solution is to ask the question in a more general way. You really want to know if the current question the user is on-- the value of currentQuestionIndex -- is as large as the number of items in QuestionList. If the app asks the question in this more general manner, it will work even when you add to or remove items from the QuestionList. To modify the when NextButton.Click event-handler you'll replace the previous test that referred directly to 3. You'll need the following blocks:

Block Type	Drawer	Purpose
length of list	Lists	asks how many items are in QuestionList
get global QuestionList	Variables	put into list slot of length of list

Your when NextButton.Click event-handler should now appear as:

The if now compares the currentQuestionIndex to the length of the QuestionList. So if currentQuestionIndex has a 4 in it, and the length of the QuestionList is 4, then the currentQuestionIndex will be set to 0 (and then 1 after the increment operation in the first row of blocks after the if). Note that, because the blocks no longer refer to 3 or any specific size, the behavior will work no matter how many items are in the list.

Test the modified behavior. When you click the NextButton, does the app now sequence through the four questions, moving to the first one after the fourth?

The current app shows the same image, no matter what question is being asked. You can change this so an image pertaining to each question appears when the NextButton is clicked. Earlier, you added four pictures as media for the project. Now, you'll create a third list, PictureList, with the names of the image files as its items. and you'll modify the when NextButton.Click event-handler to switch the picture each time.

First, create a PictureList and initialize it with the names of the image files. Be sure that the names are exactly the same as the names of the files that were loaded in to the media of the project. Here's how the blocks for the PictureList should look:

Next, you need to modify the when NextButton.Click event-handler so that it modifies the picture depending on what question the user is on. If you set the Image.Picture property to a file name of an image that has been loaded, that image will appear. To modify when NextButton.Click, you'll need the following blocks:

Block Type	Drawer	Purpose
set Image1.Picture to	Image1	set this to change the picture
select list item	Lists	need to select the picture corresponding to current question
get global PictureList	Variables	select a file name from this list
get global currentQuestionIndex	Variables	select the currentQuestionIndex-th item

Here is how the blocks should look:

The currentQuestionIndex serves as the index for the QuestionList and the currentQuestionIndex is 1, the app selects the first question and the first picture. When currentQuestionIndex is 2, the app selects the second question and second picture. Of course this scheme depends on the lists being in sync and indeed they are. For instance, the first picture, LarsenBerra.jpg, is a picture of Don Larsen, and Don Larsen is the answer to the first question, "Who pitched a perfect game in the World Series?" Test the modified behavior. Does a different image appear each time you click the NextButton?

Next, you'll add blocks that report whether the user has answered a question correctly or not. The user enters the answer in AnswerText and then clicks the AnswerButton. The app must compare the user's entry with the answer to the "current" question, using an if then block to check. The RightWrongLabel should be modified to report whether or not the answer is correct. You'll need the following blocks for this behavior:

Block Type	Drawer	Purpose
when AnswerButton.Click	AnswerButton	the behavior is triggered when user clicks the AnswerButton
if then	Control	Use the mutator to add an else. If answer is correct, do one thing, else do another
=	Math	to ask if answer is correct
AnswerText.Text	AnswerText	the user's answer is in this textbox
select list item	Lists	to select the current answer from AnswerList
get global AnswerList	Variables	The list to select from
get global currentQuestionIndex	Variables	the question number (and answer number) the user is on
set RightWrongLabel.Text to	RightWrongLabel	report the answer here
" " "Correct!"	Text	if answer is right
set RightWrongLabel.Text to	RightWrongLabel	report the answer here
" " "Incorrect"	Text	if answer is wrong

The blocks should look like this:

The if test reads, "is the user's answer (AnswerText.Text) equal to the currentQuestionIndex-th item in the AnswerList?" If currentQuestionIndex is 1, the app will compare the user's answer with the first item in AnswerList, "Don Larsen". If currentQuestionIndex is 2, the app will compare the user's answer with the second answer in the list, "Dallas Braden", and so on. If the test result is positive, the then blocks are executed and the RightWrongLabel is set to "Correct!". If the test is false, the else blocks are executed and the RightWrongLabel is set to "Incorrect".

Test the modified app. Try answering one of the questions. It should report whether or not you answered the question exactly as is specified in the AnswerList. Test with both a correct and incorrect answer (because text is being compared, the test is case-sensitive).

Click the NextButton and answer a second question. Does it still work? It should, but you might notice that when you click the NextButton, the "correct"/"incorrect" text and the previous answer are still there. Though it's fairly innocuous, such user interface issues will definitely be noticed by the users of your app.

To blank out the RightWrongLabel and the AnswerText, you'll put the following blocks within the when NextButton.click event-handler:

Block Type	Drawer	Purpose
set RightWrongLabel.Text to	RightWrongLabel	the label to blank out
" "	Text	When Next is clicked, erase old answer critique
set AnswerText.Text to	AnswerText	the user's answer from previous question
" "	Text	When Next is clicked, erase old answer

The blocks should look like this:

When the NextButton is clicked, the user is moving on to the next question, so the top two rows of the event-handler blank out the RightWrongLabel and the AnswerText.

Test this behavior. Answer a question and click Submit, then click the NextButton. Does your previous answer and the apps critique disappear?

QuizMe! Final Version:

Package the final version of the app by choosing App (provide QR code for .apk) from the Build menu. When the barcode appears, use the barcode scanner on your phone to download and install the app.

Once you get a quiz working, you might want to explore some variations. For example,

Instead of just showing images for each question, try playing a sound clip or a short video. With sound, you can turn your quiz app into a Name That Tune app.
The quiz is very rigid in terms of what is accepted as a valid answer. There are a number of ways to modify this. One is to use the text.contains block to see if the user's answer is contained in the actual answer. Another is to provide multiple answers for each question, and check by iterating (using for each) through them to see if any match.
Transform the quiz so that it is multiple-choice. The list of answers will need to be a list of lists, with each sub-list holding the answer choices. Use the ListPicker component to allow the user to choose an answer.

Here are some of the ideas covered in this tutorial:

Apps can be written in a general manner so that they work with any data list.
Index variables are used to track the current position within a list. When you increment them, be careful about reaching the end of the list.

Scan the following barcode onto your phone to install and run the sample app. (or tap on the barcode if you're viewing this webpage on an Android device)

If you'd like to work with this sample in App Inventor, download the source code to your computer, then open App Inventor, go to the My Projects page, and choose Project | Import project (.aia) from my computer ....

MIT App Inventor is grateful to Professor David Wolber, CS Professor at The University of San Francisco, for developing this tutorial.

Done with QuizMe? Return to the other tutorials here.