All language subtitles for 2. Building a Score Keeper

All right. So as I said, the first thing that we're going to do is build a scorekeeper to keep track of
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how many questions the user it got right and how many they got wrong.
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Now in order to do this, we're going to place our code at the end of our column. So our column has a number
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of children.
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It's got a couple of expanded widgets, one which is for the question and two for the answer buttons.
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Now right at the bottom here you'll see a To do. And this is what we've put into these starting file
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to tell you this is where your code for your scorekeeper should go. To dos are really helpful because
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when you're working on a large project, the first thing you probably want to do is to break it down into
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smaller more manageable bite-sized chunks. And then you're going to tackle each of those one by one until
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your final project gets built.
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So it's really easy to break down a large project into a series of to dos. And in Android Studio, in order
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to create a to do, it's as simple as simply writing a comment.
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So our two forward slashes, and then we write the word to do, and then we add a colon and afterwards we
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tell our future self or other colleagues that we're collaborating with, what to do.
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So once you've created your to do, you can find them inside the to do tab down here.
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So if you click on that, it will show you all of the to dos in your project.
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And at the moment, there's only one inside our Quizzler project and I'll show you how to find it.
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It's inside the lib folder, inside the main.dart file. But a far easier way is to simply just double
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click on the to do and it will take your cursor all the way to the place where it needs to happen.
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First things first, let's delete this to do because we're going to do it right now. In future challenges,
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we'll be setting the challenges for you,
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each of the steps in the to dos.
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So now that you understand how it works, you'll be able to use it to help you figure out what are all
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the steps you need to complete.
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All right.
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So now that we've deleted the to do, we are perfectly positioned to create our scorekeeper. And our scorekeeper
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is simply just going to be a row widget that's going to go into our column. And this row is going to
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have a bunch of children which are icon widgets.
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So we're going to create an icon widget, and we're going to say that the icon that's gonna be displayed
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comes from the material icons. And the particular one that we're gonna show is something called check.
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And you can see there's a little preview over here.
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And when you hit ENTER, you'll see it show up over here in the gutter as well.
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And this is simply just a tick.
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We can change the color of our icon to a green color so that we can further make sure that the user
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knows that when they see a tick, it means they've got the last question right.
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But we can also add a icon for when they get something wrong.
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So we'll add a icon that is the one called close.
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And this is a nice little cross for us, to tell the user that they've got the last question wrong.
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And this one is going to be red of course.
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So now that we've got a green tick and a red cross, if we hit save and check out our project at the moment,
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then we see our little row show up at the bottom.
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So this is going to be our scorekeeper.
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And as the user gets things right or as they get things wrong, we're going to add icons down here to
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keep track of their score.
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So this row is going to be building up by adding new icons like this, until the point where the user
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is done with all the questions, and then we will clear this line out and delete all of the icon widgets.
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Now we know that rows and columns can contain multiple widgets.
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So in our column for example, we've currently got three expanded widgets and a row widget. And in this
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row, we've got five icon widgets. But other ones such as a safe area or a padding widget or a center widget,
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they can only have one child.
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The difference between them is that the column widget can accept children in the form of a list.
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Now a list is simply a way of grouping data into collections.
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And this is a common thing that you can do across different programming languages.
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So if you come from a different programming language, you might know list as an array. But in both cases,
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it's a way for us to be able to group related pieces of data into a single list.
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And later on, we can manipulate the list or tap into its contents.
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Now we're going to go ahead and create a empty list, and we're going to do that right here. In order to
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create a list in Dart, we're going to write the keyword list.
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And this says that whatever variable that we're creating afterwards is going to be of type list, and
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then we're going to give it a name, so we'll call this scoreKeeper, and it's gonna be set to equal
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a empty list.
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Now when you're working with collections, you'll often see these square brackets.
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And in this case what these empty square brackets represent is just an empty list.
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There's currently no items inside the list. But we can also add items to the list when we create it in
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the same way that we did it for all rows and columns.
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So when we said that this row is going to accept a bunch of children widgets, we had our opening square
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bracket and our closing square bracket and in between are all the items in this particular list.
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Now we can do that for our scoreKeeper as well.
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I'm going to transplant some of these icons over, and I'm going to simply cut it and paste it in here.
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So now we have a list that's called scoreKeeper and it contains five icons.
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And later on if we decide that we want to use the list, then we can simply refer to it by its name.
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So I'm going to delete everything on the right hand side of this children property.
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I'm going to instead refer to my list I've created up here called scoreKeeper
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like so. Now in this case, because scoreKeeper has a data type of list and the children property for the
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row requires a list,
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then these two sides left hand side and the right hand side, are compatible which is why this works.
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Now notice that in this case, it's actually expecting a list of widgets whereas over here, our storekeeper
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is a list of data that have a dynamic data type.
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Now as we mentioned earlier, when you're using dynamic data types and a lot of things are happening, you
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can very easily get into hairy situations.
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So the best thing is to actually explicitly state what type of list it is that we're creating.
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And by that we mean what kind of data can actually go into the list.
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So for example, if I was to create a list of strings, then I could call it my strings.
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And when I create it, it would contain strings like a and b and c.
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Now in this case, the way that I could specify that this particular list called myStrings can only accept
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strings inside the list,
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I can do that by simply adding an angle bracket after the word list, and specify the data type that
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goes into the list.
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So in this case, it will be like this.
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Well now I can, for example, create my list and start putting numbers in here. Or rather integers, because
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it says that int can't be assigned to the list of type String.
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So this makes our list a lot safer so that we don't accidentally put in the wrong data type.
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Now up here, it's the same thing.
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If we want to specify that we only want a list that contains widgets, then we can simply add the word
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widget inside some angle brackets, right after our list.
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Now in this case, because we know that everything that's inside this list are icons, we can also say that
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this is a list of icons. And this still works down here because icons are in fact widgets.
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So if this particular row can only take a list that have widgets, it is still compatible.
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Now if I instead had a list of strings, which are definitely not widgets, then down here I will get an
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incompatibility error. Because a list of strings can't be assigned to a list of widgets, but a list of
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icons can.
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So let's change that back. So now when I hit save and I check out my app, you can see that pretty much
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nothing has changed. My row down here is created using my list called scoreKeeper rather than directly
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creating it inside my row. The benefit of taking out my icons and putting it into a separate list means
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that I can now add icons into my list of icons on the fly.
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So for example, I can say that when the user presses on the True button, then inside the onPressed, I'm
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going to get it to add an icon to my list of icons.
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First of all I have to tap into my scoreKeeper list and then I'm going to use something called
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.add, which adds a value inside the parentheses into the end of the list. And the length of the list will
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grow by 1.
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So we're going to say scorekeeper.add,
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and the thing that we want to add is a new icon.
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Remember that scorekeeper can only contain icons.
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So we're going to create a new icon, and this icon is going to be a check sign. And it's going to have
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a color of green.
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So now that I've created my icon and I've added it to my scoreKeeper, all I have to do is to put it inside
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a set state so that it will trigger a rebuild of my widget tree.
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And that new icon will show up inside my scorekeeper row.
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So let's go ahead and hit save to update our code. And now when I click on the true button, you can see
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a little green checkmark will get added to my row. We've been able to do this because of the power of
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Dart lists.
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Now if this concept of lists is new to you, then I recommend heading over to the next lesson where we're
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going to dive deep into Dart lists and we're going to learn more about how it works.
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Now if you're already familiar with how lists or arrays work and this concept isn't new to you, then
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feel free to skip the next lesson and head over to the lesson afterwards where we continue building
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out our app.