Flutter 38 - App Life Cycle Video Lecture | Flutter: Build beautiful native apps in record time - App Development

hey everybody it's Brian and welcome to
the 38th flutter tutorial
sorry my phone made a weird noise I had
some user feedback I really try to keep
up on my inbox but sometimes it's just
impossible
this one really stood out it said hey
I've been doing work in Android and I
want to know how to do Application
Lifecycle and flutter if you have no
idea what I'm talking about just Google
Android app lifecycle and there's tons
of graphics out here that kind of
explain there's a created a started a
resume to pause to stop and what is all
this what does it really mean alright so
if we just do our live template we're
going to run this here you see we have
the clock application open it's going to
flip over to our app so this thing is
now running now what happens if we go
back into that well cell phones are not
like your laptop sitting in front of
your desktop they run on limited power
they have batteries and they have power
constraints so what they do is when you
put an app into the background they will
pause that app and when you pull it into
the foreground they'll resume that app
so sometimes some applications it's very
helpful to know when the application is
in and out of the foreground or when
it's paused or suspended so that's what
we're really gonna look at today kind of
non visual you're gonna have to kind of
take a little bit of a leap of faith
here but that's what we're gonna do
alright so first thing we need to do is
we are going to say with widgets binding
observer bang so what this will do is
it'll allow us to actually observe the
lifecycle in pretty much real-time so
we're going to do a control oh and just
have a look around here you notice how
there is some some interesting
properties here like did change locale
did change application life style state
that sounds promising we're done we'll
definitely add that and then we're going
to just ctrl o again and we want the
init state
and let's just control Oh one more time
and we're just gonna have a little peek
here dispose there it is so now what you
can see is kind of a pattern here we got
when the state is initialized or when
its first turned on when the did change
app lifecycle state meaning when the
cycle change did it get pause resume
suspended and then when it suppose
disposed meaning it's no longer needed
remember in dart there is no such
concept as a Deconstructor so you can't
simply say hey the D constructor of this
class like you would with other
languages you have to actually track
this whole lifecycle gets a little
tricky but it's really not too hard so
we're gonna say print and it's state
super dot in that state and then widgets
whoops which is binding observer the
instance why are you not doing oh that's
why widgets binding instance dot add
observer and we're just going to add
this a current object here so what we're
doing there is we're binding to the
widgets binding instance blah blah blah
basically saying we want to observe this
objects lifecycle then in the dispose
we'll fill this out because it's pretty
easy we're just gonna do the exact
opposite here and actually pull this up
here so we can see it a little better
and we're gonna say I'm gonna say
dispose and we're gonna say super dot
dispose but we have to do this at the
end here and here we're going to remove
observer so we're going to stop watching
this object now the magic actually
happens right here in this did change
app lifecycle State and what we need to
do is to say print and we're going to
just
we're just going to print out the
current state and then we want to
actually switch on this thing it's gonna
say switch state and we're gonna say
case app lifecycle stay dot and we'll
say inactive paused why is this suddenly
griping and complaining missing claw oh
that's why it knows what we need so it
wants to force us to do everything so
we're just gonna add those in super
quick we're gonna say pause we want
resumed and suspending and then we're
just going to grab that because I want
those to stand out a little bit here
we'll say inactive paused resumed maybe
and of course suspending alright let's
actually reload that whole app and you
can see the first thing happened was in
it state ooh where is it
do a full restart on this thing sounds
that restarted mmm did I break it I have
a very good knack of breaking things
we're just gonna clear everything out of
here started again maybe that's a bug
and flutter I don't know all right so
we're gonna start this whole thing again
disclaimer alert flutter is still an
alpha but I have a habit of just
horribly breaking things so okay so
there is our net state right here bang
and what we're gonna do is we're gonna
actually and you see as soon as we click
that it's still kind of there it's in
the app chooser you can see how the
state equal life cycle paused and we go
back resumed
so that's kind of what it would do so if
we were to let's just clear this out
where's my dart analysis it's not
working darn it I got to figure out why
that doesn't work anyways so if we go in
here and we just go in here and we open
the like say the clock you can see how
our app is paused and then if we just go
back in you can see how the state equals
resumed and resume and life goes on now
let's clear this out and let's actually
kill our app and see what happens here
you can see how lost connection to
device but nothing actually happened we
didn't actually get it disposed there
kind of little disappointing there and
it might be a bug in my code not
necessarily in flutter itself but gives
you a rough idea how to actually
interact with these now what would you
use them for well let's say you're
running like a live video feed or
something well whenever it gets paused
you want to actually pause that video
feed you want to stop downloading
because the users no longer looking at
it and you're just chewing up their
battery and then when it resumes when
they pull it back into the foreground
that's when you would start it again and
it disposed are a little bit different
and it is where you would like load the
settings off the disk or download from
firebase where dispose would be where
you would clean everything up and I'm
kind of a little wondering why I never
got to dispose here I'll have to figure
that out but I hope that answered your
question I know it took me a while to
figure this out and there really wasn't
a whole lot of clear examples out on the
web that I found maybe you'll have
better luck but at any rate thank you
for watching I hope you found this
educational entertaining source code for
this obviously will be out on void roms
comm you just go to tutorials and then
github and be sure to join the void roms
Facebook group