Flutter 15 - Static Video Lecture | Flutter: Build beautiful native apps in record time - App Development

hey everybody its Brian welcome to the
15th flutter tutorial we're gonna
continue on our learning curve of Dart
we're actually getting towards the end
of this here if we go ahead and jump
into language and then do a tour of dart
you can see that we've covered pretty
much all of this today we're going to
backtrack a little bit and go back into
classes a little bit here I want to
discuss static that my brain just should
not static methods and static variables
inside of classes and how they actually
interact a dart so let's just go ahead
and crack this open we're just gonna
call it stat I like that word stat so if
you are from another language you're
probably rolling your eyes go and I
already know how this works there are
some minor caveats if you're brand-new
programming this may completely blow
your mind and I apologize in advance so
we're going to just kill that kill that
and the first thing we're going to do is
we're going to make a new class here and
we're going to call it counter
now in the counter class we're going to
make a private variable here static and
let's call it count so what is a static
mean right here static is a keyword you
can tell it's a keyword because it's
highlighted in bold really what it means
as it exists throughout every instance
and non instance of that class and we'll
really get into that here in a second
but just understand that it means it
always exists so what we're going to do
is we're going to say int again we're
gonna make a getter and setter for this
I swear my phone is dying it just made
the weirdest noise now why am I making a
getter and setter we really don't have
to I'm just doing this to show you that
you know you can have this as a private
member variable but also have it static
some people get a little confused and
think that just because it's static it
has to be public and it really doesn't
so now we're going to make some static
methods here
so we're just going to increment and
decrement respectively and then we're
going to make some non-static methods
here and actually we can just shorten
these up as well I don't know why I was
going to do it this way but so we can
add remove ten respectively and then we
are going to just print the count out
now you may be looking at this and
asking some questions what is static why
is it all scattered throughout this and
how come we're using count and not the
getter and setter remember a getter and
setter are primarily used for outside of
your class well you're in your class you
have the inner scope and therefore you
can access this internally everything
outside of this because this is a
private variable will not be able to
access it so you have to use the getter
and setter and now we're going to go
over to our main file here we're going
to in point the oops
man that was a major fail right there I
was kind of embarrassing so first thing
we want to do here let's just say
counter and you notice how if we just
type the class name counter we have the
decrease increase in print count and if
we look at the class again you can see
that increased decrease in print count
all have static that's what it means is
we don't have an instance of this class
yet we have those functions or I should
say those methods and we can actually
work with those
so we don't even have an instance of
this but yet still it works
we've gone from zero to one and we can
actually increase this a few times if we
want
now one thing you should notice is we
don't have access to the non-static
fields and that is simply because
they're not static meaning you have to
have an instance of that object all
right so we're going to say counter obj
just short for object you notice how now
we have access to the non-static fields
but we do not have access to the static
fields so we have access to add 10 but
we don't have access to increase or
decrease
oops boys screwed that one up and this
is why we're using our getters and
setters so we can access those and we're
going to dereference that object and
once again we're going to print the
count so what we're going to do here is
we're accessing the static fields and
then we're going to make an instance of
that object and modify it with an
instance of that class my instance of
that object didn't make any sense we're
make an instance of that class we're
making an object and then we're going to
modify it using the non-static fields
and then we're going to actually print
the count out again and we can see how
the count actually increments so we've
got 0 2 because we've gone from 0 plus 1
plus 1 so there's our 2 and then we have
gone to 12 because we've added 10 and
then we've set it to 5 so there's our 5
and then we've set it to null and we set
our object to no but yet we can still
print out 5 and if we made another
instance of this class
that's called this obj 2 so we know it's
a completely different object
let's get rid of that right there
you can see that it stays at 15 because
now we've added ten to the five and even
though we've set this to null it still
stays there so that in a nutshell is
static fields now one thing you should
know is you don't always need static a
lot of people think I need to convert
this to static and that to stat you
really don't many times what you would
actually need to do is persist this off
to a storage device somewhere rather
than actually holding it in memory for a
counter it would actually make sense
like let's say you're we're building a
like a Humane Society that houses
animals and you want to know how many
animals are in there every time an
animal's added or removed you would
increase the counter but for normal
lists and things like that static really
does not make a whole lot of sense what
is a good use case for static well this
right here actually if you want to make
a what's called a utility class or a
class that has a lot of functions in it
or methods in it that you would just use
throughout the day rather than having to
actually build an instance of that
object you can just say class dot
whatever it is and then you've got all
your built-in functionality there's
actually a lot of libraries that do that
so that's a good use case that's all for
this tutorial I hope you found this
educational entertaining the source code
for this and all other tutorials will be
out on void roms com and you just click
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