All language subtitles for 7. [Dart] Enums

Now in the last lesson we learned about the gesture detector and we added it as a parent to our reusable
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card,
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at the top. The ones with our male and female icons.
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And we created a method called updateColor that allows us to select one of these genders and be able
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to activate these cards by changing their color.
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Now at the moment our code works just fine.
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But it's a little bit wordy and also there's a few things that are not so great.
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And the first thing that comes to mind is the fact that we're passing in a integer to represent a gender.
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So we're saying that one is going to equal male and two is going to equal female.
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So that's why we're checking to see if the gender is one then that means the male card got pressed.
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But if the gender was two then that means the female card got pressed.
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Now as you can imagine, if you came back to this code in six months time or if somebody else was looking
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at it, they might get a little bit confused because it doesn't make a lot of sense.
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And even though we have a lot of comments here it's not great.
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So how can we solve this? In this lesson,
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we're going to address all of this by learning a concept in programming that is super useful which are
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Enums. Enums stand for enumeration.
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And if you look it up in a dictionary, it means the action of establishing the number of something.
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And that's kind of what we've been doing here right?
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We've been establishing that the male gender is the number one and the female gender is the number two.
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But this is super painful and quite confusing.
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But in programming, this need crops up very frequently.
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Say if you're trying to encode different types of cars in your app and you say that we have this thing
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called carType and if it's equal to one, then it's convertible, if it's equal to two then it's an SUV,
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if it's three then it's a hatchback.
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Now these numbers don't actually inherently have any meaning.
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And we're actually assigning it a meaning and trying to remember it down the line. And trying to force
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other people who we work with also to follow this convention, and that's difficult.
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But imagine if instead, we can actually give it a word which already has meaning.
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So if we said that the first one has a carType of .convertible and the second one was .SUV or
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third one was .hatchback.
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That makes a lot more sense and is a lot easier to work with and you can see at a glance in the code
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what it is that we're talking about
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when we're coding up these different types of cars.
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If you imagine that we already have booleans which we know to be either on or off or true or false, and
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is a bit like a light bulb. It's very binary right?
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It has two states, on and off.
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But what if we wanted more states, then a light bulb can hold.
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Well then that's where we kind of start using Enums. And I would say that you names are almost a bit
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like a blender where you have multiple options right?
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You might have a high setting, you might have a low setting, you might have a medium or a juice or a blend
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or alter blend, whatever it may be. And it's more than just on or off.
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There's many different options and that's exactly what we use enums for, when there's a lot of different
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options that we want to be able to encode and not just have to rely on numbers.
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And we can actually give each of the options a name that has meaning. An enum looks like this in Dart.
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We first start out with the keyword enum, to show that we're creating an enum. And then we give the
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enum a name.
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So it could be carType or it could be gender. But the naming convention for enum names are the same
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as class names.
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So there are camel cased but they start off with a capital letter. And then we have a set of curly braces
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that describes each of the different types.
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So say typeA, typeB, typeC or hatchback, coupé, convertible.
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And then when we actually need to use the enum, then we can simply writeEnumName. typeA or .
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typeB. Let's head over to a Dartpad to see this in a little bit more detail.
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Now let's say that we had a class of Car and previously we only had things such as number of seats or number
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of doors, which makes a lot of sense to use an integer for right? Five doors is literally an integer.
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But if we wanted to encode a carStyle then we might have to use an integer and we have to make a note
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to ourselves that remember that you know if this is one then that means it's a hatchback.
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And if it's a two then it means it's an SUV etc. which is quite painful. But it does mean that if
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we decided to initialize our car,
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say we create our constructor and we set our this.carStyle when we create the car.
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Then we could go into our main function and we could create a new car.
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So let's it's a data type of car.
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Let's call it myCar
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and it's going to be equal to a car that's constructed.
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And we have to give it a carStyle and let's say it's equal to an SUV.
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My car's an SUV.
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Now if you read this line of code, it makes absolutely no sense whatsoever to a human unless we add a
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whole bunch of comments to say that, oh actually this car style 2 means that I'm creating a new SUV.
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Now it's good practice to have comments that explain the logic of your thinking of what your program
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does.
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But it's not great when you need comments to be able to understand what's actually going on in a particular
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line.
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And this is a classic case where enums can come in and save the day, because if we lost all of these
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comments and we came along to this code two months later, then this makes no sense whatsoever. So what
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if we created an enum?
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So let's do this here outside of any other classes and we're going to use the enum keyword to say
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that we're creating a new enum. And the enum is going to have a name which is going to be a capitalized
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camel case.
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And we're going to call it CarType.
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And then we open up a set of curly braces and we add all the different car types that we might want
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in our program.
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So we might have hatchback, we might have a SUV and maybe a convertible. And let's just add a coupé
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just for fun.
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So we've now got four types of cars and they're enclosed inside an enum and now we can use these car
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types.
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So instead of having a car style that's represented by an integer, we can change the data type to a enum
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type,
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so our carType. And now when we initialize our carStyle, instead of writing 1 for coupé or 2 for
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hatchback, we can actually provide the enum as a named value.
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So we could write carType. and you can see that we're already getting all of our values in our dropdown
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list.
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So let's say that we're creating a new convertible.
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Then we've got myCar, which is created from the car constructor, and the property for its carStyle is
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a convertible carType.
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Now look at how much better that reads.
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Even if I came back to this code a million years later, well maybe I'd already be enslaved to the computers.
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But either way if I came back to this after a long time, this line of code still makes a lot of sense.
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So let's head back to our code and here's the challenge for you. Create a gender enum at the top of file.
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You can't create enums inside classes. So make sure it's outside of any of the other classes, maybe
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somewhere below the constants. And then use that gender enum inside our update color and inside our gesture
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detector to be able to say that, in this case it was the male card that was pressed
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and in this case it was the female card that was pressed so that we can process it differently inside
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this updateColor method.
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So pause the video and try to upgrade your code by using Dart enums.
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All right.
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So first things first, we're going to create our enum using the enum keyword. And we're just gonna call it
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Gender but we're going to make sure it's capitalized at the beginning to show that it's not the same
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as a variable or a constant.
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Now gender is going to have only two different values and it's going to be male and it's going to be
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female.
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So now we can use this enum gender.male or gender.female in our code. For example our updateColor
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can now instead of taking a int type input, we can have it as a gender type input so we can either leave
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that name as gender or if you find that a bit confusing, you can change it to selected gender, just to
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know that it's the name that we're giving the input. And now we can check to see that if the selected
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gender is equal to, not one, but gender.male, then we should do all of this but if the selected gender
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was instead equal to gender.female then we would do all of this.
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And now in our code here where we update color, instead of passing in one, we can pass in gender.male and
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over here we can pass in gender.female.
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So now look at how much better our code reads. When this card has a tap detected, we update the state
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by updating and update the color and we tell it that the female card was pressed. And then it goes into
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our updateColor method and it checks to see if the gender was male that was selected or if the selected
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gender was female that was selected and then we carry out all of the rest of this code.
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So enums are really useful when you have more than one option for a property.
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So things such as car types or high-low medium settings or in our case genders male female etc. It's
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really really useful to clean up our code and make it more expressive. But still our problem is that
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our code is so wordy that it's actually painful to look at.
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So in the next lesson, we're going to learn another thing that we get access to in Dart which are ternary
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operators. And we're going to clean up all of this to reduce it down to maybe one or two lines of code.
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So if you're ready for all of that magic, head over to the next lesson.