All language subtitles for 29. Enums & Multiple Constructorfs

So what's up with TextAlign.center and EdgeInsets.all? These are certain Dart features, not Flutter

specific and they're not exactly the same.

This here is a special constructor, EdgeInsets has multiple constructors and you can see them here

if you add a dot after the class type, so without parentheses, then you see all these constructors here.

Now these features exist to allow you to create an object in different variants.

Now it can always be nice to look into the raw source code to understand what's going on and you can

always do that by holding command on MacOS or control on Windows and then you hover over the thing

you want to learn more about and it now turns into a link which you can click and if you do click it,

you're taken to the framework code. We see that enum

I was talking about, you create it with the enum keyword here as you can see and we'll do that manually,

later we'll create our own enums, for the moment let's basically ignore that, these are just different

options we have for alignment here which are then picked up by Flutter once we assigned a value to align

our text per the option we chose here.

What's more helpful is diving into EdgeInsets here.

So if we dive into this, we now see it's a class that extends EdgeInsetsGeometry, which is interesting

because you might remember that if you hover over margin,

this takes EdgeInsetsGeometry value,

So it's good that EdgeInsets extends this,

this means that if we instantiate EdgeInsets, we automatically get an object of type EdgeInsetsGeometry

because if you extend, if you have a class that extends another class, that class that does extend always

has its own type as well as the type of the class it did extend, that's also a default behavior of Dart.

Now in here, we see that there are a couple of special constructors here,

we repeat the class name, which always means it's an instructor

but then instead of directly adding parentheses thereafter, we add dot some name and that is a Dart feature

which allows you to define multiple constructors per class.

Now without diving too much into the internals here, in the end that just means that each constructor

creates a new instance of this class but with different configurations, with different settings and that

all is just done to make it easy for you to create different EdgeInsets, which is basically a settings

container setting up spaces. Setting up different EdgeInsets containers with different configurations

with these utility functions here, with these utility constructors. If I go back to DartPad, we could

have created that for person as well, we could have added our own constructor by adding the name and

then dot and then any name of your choice, for example veryOld and in there, we could have accepted

the name and then said that this constructor by default sets age equal to 60.

So here, we can't set the age in the constructor, it's always set to 60 and

we can only set the name.

Now this would be a helpful constructor if we wanted to create a person, p3

that always is 60 where we only want to set the name.

So we could use the veryOld constructor and set this to Max again,

so my name again and now if I print p3.name and I then also print p3.age, if I run this

now, you will see that here we actually get Max and then 60 being printed and that is the output for

our p3 object.

So these special or these extra constructors are really just there to give you the same type of object

you would get with the normal constructor but with some predefined settings, some different behaviour

they run inside of the constructor.