All language subtitles for 8. Creating a Question Class

All right.
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So now that our app is able to show the questions in our list of questions and also match up the questions
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with the answers to check to see if the user got the right answer.
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But at the moment it's a bit clunky.
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We've got two lists that are tracking things that should be associated with each other because this
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is the answer to this question and ideally it would be great if they were stored together somehow.
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So how can we do this?
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Well we can create a new class. Just as we have our widgets which have different properties such as a
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child property or a padding property or a flex property,
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we can also create a class that have a question property and a answer property, so that we can associate
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the questions and answers together in a single object. In order to do this,
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we're going to go into our lib folder where all of the action happens, and we're going to right click
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and go to new.
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I'm going to select to create a new Dart file, and you're going to call this Dart file question, because
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that's exactly what it's going to represent.
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And then it says, 'do you want to add this to git?' You can either click yes or no.
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It doesn't really matter in this case because we're not really using git for this project.
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So in order to create a new class, we have to use the keyword class.
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And afterwards we give our class a name.
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So in this case, we're going to call our class question. And it's by convention that when you create a
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new class, it starts with a capital letter just as all our classes down here, say our Quiz page or our
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widgets all start with a capital letter, because they each belong to a different class.
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So over here, we've created our question class and we're going to open a set of parentheses to define
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what is so special about this question class. The question class is only going to have two properties,
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and they're going to be properties that every question should have.
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So one is going to be a string and it's going to be called the questionText, and the other is going to
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be a boolean and it's going to be questionAnswer.
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Now inside this question, we also have to give these variables a value when we create a new question.
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In order to do that,
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we have to create what's called a constructor. So that when we construct this question object, we give
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it some values for the question text and question answer. And we do this by writing, the same as our class
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name, question. And then we open a set of parentheses and then I'm going to add some curly braces and
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this is beginning to look a bit like our functions.
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This is where our inputs would normally go. Well in this case these are the values that we're going to
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provide when we create a new question.
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So we're going to have a string that's going to be called q, and we're going to have a bool that's going
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to be called a. And you can see where I'm going here.
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Inside these parentheses that I've just opened up, we're going to set this question's questionText to
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equal the value of q, and then we're going to set the question answer to equal the value of a.
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And this part of the code has a special name.
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It's called a constructor.
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So now that we have this structure for a question object, we can create a new question object in our
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main.dart
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So inside here, let's create a new question object and we do that by specifying its type.
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So this is a new question type. And at the moment, it doesn't know this class question. This is undefined
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class question, but it's right here
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right?
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So how do we tell this file about this file?
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Well we have to import it.
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So let's write our inputs.
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And here we write our question.dart file.
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So now that we've imported that file, then the error goes away and it now knows about the question in
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class.
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So we're creating a new variable which has a data type of question.
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And this is gonna be called, let's call it q1. And we're going to set it to equal a new question and
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we're going to use that constructor that we built over here.
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We're going to provide a q and we're going to provide an a.
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So when I hit enter, you can see I can tap into the q property where I'm going to put in the first question
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right here. And this is expecting a string so that satisfies the criteria, and then I'm going to put in
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a a which is going to be the answer for the first question, which is just a false which is a boolean.
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So now I've created a new question object from my question constructor which I built over here. And my
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new question q1, now has some question text which is set to whatever I put in here and it has a question
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answer which is set to equal what I put in here for the a.
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So now what I can do is, I can say print q1. question Text or print
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q1. questionAnswer. And notice how these two pieces of data are all associated with that object
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that I created up here, and then no longer separate like how we had it up here. And we don't have to make
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sure that they each match in that order in the list. The data for the text and the answer are now grouped
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together in this object called
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q1. Now instead of having our list of questions and answers, here's a challenge for you.
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Can you figure out how to create a list of questions instead, using the questions and answers that we
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have down here?
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So pause the video and see if you can complete this challenge.
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All right.
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So let's go ahead and comment out all these lines of code. And right below,
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we're going to create a new list and the data type of the list are question objects.
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So it's gonna be a list of questions. And you can call it anything you want but I'm gonna call it a question
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bank, and I'm gonna set it to equal a new list
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using that square bracket notation. Now inside the list, I have to create some question objects. And I'm
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going to create it exactly the same way as I did up here for q1.
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I'm going to use the question constructor. I'm going to provide a value for q, which is the first question,
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and then I'm going to provide a value for a, which in this case is false.
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So now let's go and create our next question and this one has a cue of this string.
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And the a should be set to true. So let's put that here.
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Now finally, we're on to our last question and we just have to provide our q and or a just as we did
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before. And this one is also going to be true.
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All right.
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So now we have all 3 question objects inside a list that contains question objects
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and it's called our questionBank.
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So we have no need for any of this anymore.
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And it's now very succinctly linked up our questions with our answers for every one of our questions
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in our question bank. So you can either delete all of this code or you can keep it around as a comment
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if you want to refer to it.
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But I'm going to get rid of it.
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So now we have some errors and we can tell that we have errors because Dart analysis tells us that.
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But also you can see at a glance on the right hand side, when you have a little red button there it tells
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you, you've got errors. In order to find our errors, we can see there's one here there's one here and there's
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one here.
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And if we scroll down, our first error is here. The text inside our text widget. Because previously, we
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had a list called questions and we pulled out the item at whichever one questionNumber is at.
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So at the moment, it's the first item in that list.
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But now questionNumber is gone,
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so how do we get it out of the question bank?
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Well it's pretty much the same way. We tap into our list called questionBank.
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We pull out the question at this index.
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So it'll be a question bank at index 0 when we first start up our app.
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So we now have access to this question object. But that doesn't work because our text widget needs a
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string.
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So we need to display this part which in our question class, is known as the questionText. So we can
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simply write question bank at this index, .questionText. And now we'll be able to do exactly the same
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thing but using our new question bank instead.
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So let's scroll down and fix the next one.
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The next issue is here, and we used to have our answers list but now that's gone and is replaced by our
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question bank.
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So we're going to get the correct answer by tapping into the question bank at a particular question
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number, and then we're going to write .questionAnswer.
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And that of course comes from this property right here which is set to the value of a, when we create
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this question object. Now that we've addressed that one, we've got one more error to go and it's right
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here.
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And it's exactly the same as before, question bank at the index of question number .questionAnswer
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to get the correct answer for the current question. So we fixed all our errors and if we save and go
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ahead and hot restart our app, then it should reset our question number back down to zero, and we should
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start on the first question.
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If we click true for this question, you can see that down here, we get user got it wrong because the first
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question's answer is false. And you can progress through this of course until you run out of questions
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at which point it'll crash out again.
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But now, we've organized our questions and answers together into what's called an object. And we created
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our objects by creating a class. So if the concept of classes and objects is unfamiliar to you and you're
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not quite sure what's actually going on here, then be sure to head over to the next lesson where we do
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a deep dive on classes and objects and how they work in Dart.
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Now if you're very familiar with this and you can understand how the constructor works and how our classes
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are created and how our objects are constructed, then feel free to skip the next lesson and continue building
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out our app.