App Development Exam > App Development Videos > Flutter: Build beautiful native apps in record time > Flutter 17 - File IO
Flutter 17 - File IO Video Lecture | Flutter: Build beautiful native apps in record time - App Development
FAQs on Flutter 17 - File IO Video Lecture - Flutter: Build beautiful native apps in record time - App Development
| 1. What is Flutter 17? |  |
Ans.Flutter 17 is a version of the Flutter framework, which is a popular open-source UI development kit that allows developers to build cross-platform applications for mobile, web, and desktop using a single codebase.
| 2. What is File IO App Development in Flutter? | |
Ans.File IO App Development in Flutter refers to the development of applications that involve reading from and writing to files on the device's storage. It enables developers to store and retrieve data in files, such as text files, JSON files, or image files, which can be used for various purposes, such as data persistence or content management.
| 3. How can I read a file in Flutter using File IO? | |
Ans.To read a file in Flutter using File IO, you can follow these steps:
1. Import the 'dart:io' package.
2. Create an instance of the 'File' class with the file path.
3. Use the 'readAsString' method of the 'File' class to read the contents of the file as a string.
4. Handle any exceptions that may occur during the file reading process.
Example code:
```dart
import 'dart:io';
Future<String> readFile(String filePath) async {
File file = File(filePath);
try {
String fileContent = await file.readAsString();
return fileContent;
} catch (e) {
print('Error reading file: $e');
return null;
}
}
```
| 4. How can I write to a file in Flutter using File IO? | |
Ans.To write to a file in Flutter using File IO, you can follow these steps:
1. Import the 'dart:io' package.
2. Create an instance of the 'File' class with the file path.
3. Use the 'writeAsString' method of the 'File' class to write the content to the file.
4. Handle any exceptions that may occur during the file writing process.
Example code:
```dart
import 'dart:io';
Future<void> writeFile(String filePath, String content) async {
File file = File(filePath);
try {
await file.writeAsString(content);
print('File written successfully.');
} catch (e) {
print('Error writing to file: $e');
}
}
```
| 5. Can I use File IO in Flutter for both Android and iOS platforms? | |
Ans.Yes, File IO in Flutter can be used for both Android and iOS platforms. Flutter provides platform-specific implementations for file IO operations, allowing developers to read from and write to files on both Android and iOS devices using a unified API. However, it is important to consider platform-specific file system restrictions and permissions while implementing file IO in Flutter.
Text Transcript from Video
everybody's bright and welcome to the
17th I better double-check that 17 yes
17 sitar his flutter got a little
frazzled err my phone was kind of
beeping in the background anyways we're
gonna continue on down our flutter
tutorials we're gonna learn a little bit
about IO
now when I say IO I don't mean the moon
Io I mean input/output and the first
part of input/output we're gonna work
with is called files and directories
files and directories is a huge topic
and we're gonna kind of condense it down
a little bit so obviously we can't cover
every single little use case but we're
going to cover the vast majority of them
we can't cover everything because we
will be here for 300 more videos you can
do just about anything with files you
can encrypt them decrypt a Minko time
decode them pump them across the network
scramble them up chop them up dice and I
mean whatever you want to do I sound
like an infomercial but files are quite
literally the bread and butter of most
programs so without further ado let's go
ahead and import dart convert dart IO
and let's work with this so first thing
we want to do here is let's say we want
to figure out how to list files and
directories in a path here so I say void
list if I actually did that correctly
and we first want to surround this with
a try-catch block
now why do we want to do a try-catch
block first it's because working with
the file system can be very error-prone
you ever worked with an older OS or a
computer that's kind of flaky you'll
know that really quickly that sometimes
files just do not play nice all right so
whoops well new alright so what we've
got here is we've got a directory object
and we're just going to make a new
directory object based off the path then
we're going to say now if you notice how
we can say exists and exists Inc this is
kind of the crux of the i/o portion of
dart io is asynchronous so what they've
done is they put some helper functions
in here that allow you to help you call
this synchronously so instead of doing
exists and then messing around with a
wait and then and you know futures and
all that we're just gonna do these sync
and let them do all the heavy lifting
for us so if it exists then where you
get file sensitive entity and we want to
list a sync then we're going to just
print out
so first thing we want to do here is
actually let's get a listing here so
we'll see we're just going to I'm on the
Linux system so just gonna grab the root
path users you might want to do that on
your C Drive let's just run this and see
what happens here you can see how we get
a whole list of things these are this is
everything that is on my root path here
if you've no Linux it's really nothing
special on this virtual machine
alright so whoops I got a positive eight
for one second here so how about that
somebody was at my front door so I had
to go see what it was all about we're
gonna change this path here and it's
just the path that I have the videos in
that way we're working with a very small
section of my file system so if I goof
up I'm not reinstalling my operating
system here although on Linux it's
really hard to actually blow something
up you can see how we actually have a
different structure now and this is
actually the movie that we're creating
at this very point in time so what we
want to do is we want to learn how to
write to a file
pool and this is just the way I do it
there's the problem with programming or
I should say the added bonus with
programming is there's literally
billions of ways you could do this I'm
just doing it my way if you don't like
it feel free to do it your way but this
is typically what I do when I'm writing
a program alright so we're going to do
the try catch block we did screw
something up up here
now if you're wondering why I'm doing
just a print to string it's because I
want to know when something actually
blows up the last thing you want is a
what's called a silent error which means
you have a catch and then you don't do
anything with it because then you run
your program and nothing happens and
you're like what the heck
so you want to know that there was
actually an error and that's why I just
print it out but all right so when you
say file so we're just saying want the
file object to be a new file based off
the path that we're giving it and I
probably should name this the path but
I'm just gonna leave it as file and then
we want to say a random access file I'm
gonna call this RF equal new random
access file actually nope sorry I
screwed up we want to get that off of
our file reference sorry about that and
we're going to say open sync now you'll
notice that there's open read open which
gives a future and then open write open
sync we're just going to work with open
sync there's different types of files
we're gonna work with what's called a
random access file meaning we can
randomly move around in that file and do
whatever we want with it
I typically work with random access
files because they're a lot more
flexible although they are a bit slower
technologies grown to the point that the
difference between a random access file
and say a sequential file is very
minimal and then we want to actually
give it a mode and the mode here is
going to be the mode that we give the
function or I'm sorry the method if
you're wondering what the mode actually
means you can actually say file mode
dot and see the different modes there's
a pen there's readers write write only
and write only app and append basically
takes an existing file if it exists if
it doesn't exist it creates it but let's
just say it exists and it just keeps
adding to the end of it think of it like
a line in the bank it'll just keep
adding to the end
read will read from the file write will
completely destroy the file and write it
from scratch think of writing as you
know you take your parent a bad report
card they wadded up into a ball throw
out the trash and say bring me another
write only means you can only write to
the file and write only append is pretty
self-explanatory
you can only append to the file why they
didn't call it append only I don't know
but all right so those are the different
modes and that's pretty standard of most
operating systems regardless of what
platform you're on that's kind of like a
file primer you probably spent a week
talking about that new computer science
class all right so what we want to do
now is we want to write string a sync
and we're going to just say data and
then we want to flush sync and we want
to close sync so flush and closed those
are real key words kind of ignore the
little sync at the end here for now SiC
just means that we are asking dart to do
this synchronously focus on flush and
close
what flush does is think of a file as
well like a toilet I hate to say it that
way but think of it like a toilet and
you're just dumping stuff into it and
when you're done you want to flush that
toilet write it down to the desk so
flush literally tells the operating
system hey write it down to the disk
closed then closes the file I am not
100% certain but I think under the hood
close may call flush for you I know on
some some different languages it
actually does I'm not sure if it does in
dart so I'm gonna call the flush
intentionally because that is what was
out in the actual code they had as an
example out here somewhere I'd have to
find it yeah right here writing file
contents I think they're doing this
because their example is asynchronous
and I'm doing it synchronously so I'm
not sure if I actually need to do the
flush I think I just need to close all
right so now that we know we can write
to a file we need to know how to read
from a file this is a little bit easier
and we're going to say a string and
we're gonna say read file
all right so we're going to just do our
try-catch block now for some of you
while I'm typing this out maybe reading
the comments out on YouTube there's a
lot of folks saying hey you know we
don't like these tutorials we want more
cute or qml or why are you using dart
and not cute and qml it's because I've
done a lot of other tutorials in another
language called C++ that uses a library
or I should say a bunch of libraries
called the cute I don't want to call too
cute framework because it's a cute
library but it's called cute and it is
kind of lost my train of thought here
hey it runs on any platform it's an
amazing system
I still love cute I still love qml and I
want to do more videos on that but right
now dart and flutter really have my
attention so that's just kind of my
focus and we're going to say
read as string sick now what we're doing
here is we're just saying create a new
file with the file name which creates
the file object now that we have the
file object F in this case we're saying
F read as string sync mean that's going
to read the contents of that entire file
into one giant string and then return a
variable we are then going to take that
variable and return it from this method
and what we're doing here is the default
encoding which is utf-8 which is an
entirely different conversation encoding
is how the actual information is written
and read to and from the disk in this
case we're going to leave it as utf-8
you can feel free to experiment and
change your encoding but just understand
that not all in codings are compatible
so we're just going to leave that as
default all right so now we have the
ability to write and the ability to read
let's test this out let's actually just
go here and we want to say we need to
make a another variable here hmm let's
call this let's call this txt file and
we're going to just say just give it a
very simple name or say if write file
and we need to give it our text file and
we need to say some sort of data that
we're going to write to we're going to
say and then the mode we're going to say
a patent and we're just gonna play
around with this for a little bit oops
so really what we're saying if this then
that so what's going on under the hood
assuming this works is we haven't
actually tested the code we're going to
write to our text file which is going to
be on this path in my virtual machine
and we're gonna write this data this
right here is called an escape character
and this right here is called an escape
sequence wow I misspelled world that's
embarrassing
so what escape does is it escapes out of
the character sequence and says I want
to put a special character in here slash
n stands for new return you can if
you're in a Windows machine I think it's
slash and / R or / r / and like that
actually it's the other way around I can
already tell by looking at its RN which
does a hard return a new line that's how
Windows does it but on Linux and Mac
it's just a new line you can also put
like a tab in there you can put special
characters you can put just anything you
want
we're just doing this to break it up so
they'll be in line we're doing that
because we're in append mode and we want
a new line every time we run this then
we're going to print and we're just
reading the contents of the text file
back that we just wrote and we should
see hello world down here when we run
this and you see bang hello world so if
we go out to our file system you see
that now there is a txt dot txt our test
dot txt and if we were to open this up
you can see there is hello world in
there now let's just move this off to
the side we run this again and you see
there's two now there's three now
there's four and you can see our text
files saying hey it's changed we're
going to reload it and that's a pen mode
it just going to keep going and going
and going now we're going to switch this
to write mode notice how we only have
one hello world and if we go back to our
text file reload it there's only one
that's the difference between write a
pen a pen is just going to keep adding
to it we're right it's going to
completely blow it away and start from
scratch I'm going to switch this back to
a pen because I want to put that up on
github the way it is
now let's say hmm we want to be able to
let me think about this for just a
moment here let's say we want to be able
to actually pump this out as JSON so
let's do that wasn't going to do it but
I'm like yeah why not people are gonna
ask how to do it so we're gonna say
before we do that I'm actually gonna do
something else
list sorry for being so scatterbrained
I'm kind of deviating from my original
plan here I'm trying to think in advance
of what people are going to ask for and
what they always ask for is okay it's
great that you can do it in one giant
blob how do you do it in a bunch of
lines you know how do you read lines
from a file so I'm just trying to limit
the number of questions that I'm gonna
get off of this thing and what we can do
here is we can just say very simply and
then we can just say
Red Lion sink and you can see how that
is currently going to return a list of
strings and it's that easy right there
we could just read the lines so let's
actually do that and let's comment this
out actually let's not let's say see
whenever I deviate from from the plan
here things happen very badly but that's
when we probably learn the most so let's
let's try this txt file so we want to
get the length of this let's run that
and you can see how there's two there's
three there's four there's five there's
six so there's six lines in that that
list object so that is how you would
read the individual lines and I'm
actually gonna comment this that was
embarrassing
Wow I really just spelled all of that
so what red lines does is it goes in and
it looks for that escape sequence of
slash on or /r or both and it actually
breaks those up into individual strings
so it's taken that giant string and
breaking it down into six individual
strings alright now we're going to go
ahead and we're going to read and write
some JSON here
so let's actually alright let's say pool
two let's say she's not to file I'm
having a hard time figuring out what I
want to call this there we go and it
will say string file now what we're
gonna do here is a little bit different
what we're gonna say is map and then we
want a string and an int we're just
going to basically plagiarize what we
did on our last tutorial here yeah I'm
getting hungry like just sitting here
something my stomach just starts
growling so I'm gonna put it absence and
we're gonna say Ryan yeah I've had a
couple people say what is cute what is
qml why are people getting upset that
you're not working on it that's why I've
just I've done like a I don't remember
how many I think like 150 hundred
seventy some of my videos a lot I've
done a lot of those videos and I've
gotten pretty advanced in that realm so
anytime I make something that's not cute
or qml everybody kind of wonders what
the heck is going on yeah I'm gonna get
back to it eventually I'm actually
hoping it back to it this winter alright
so we're going to say string Jason oops
strain data well Jason dot encode and
we're going to encode this map and then
we are going to return our right file
and we're going to say the file name our
data and then our mode we want this to
be file mode not right reason being if
we have a pen will have multiple JSON
objects in there and it'll probably
crash the program or it will just get
garbage back or we won't get the latest
object something bad will happen all
right so we've got JSON to file actually
let's call this write JSON there that's
better now I'm happy with it now we're
gonna say void we're gonna read the JSON
I fought JSON for a long long time I was
really into XML I did not like Jason
when it first came out XML is just been
around forever but it's horribly
inefficient
all right string data equal and we want
to actually read the file so we're just
reusing the code that we wrote so rather
than reinvent the wheel with the right
file and read file we're just reusing
our functions here now we need to do a
little bit of error handling here you
notice how right JSON is just returning
the value of right file now with this we
can't do that so what we need to do is
say if data that is empty then we're
gonna say print no data
and then we're just going to return out
of this function and we should also get
the error string from the actual right
here in the actual method all right now
now that we know that we have data
because at this point we should have
data I say map
string int this is the structure of our
map here structure of our map that
really didn't make a whole lot of sense
but I think you guys knew what I meant
all right so we're gonna say people
equal Jason D code and we're just going
to decode that data into an actual
object and then from there we're going
to say print we want to know what the
people object contains just so that we
can prove that we actually decoded this
we're going to say people not for each
and then we're going to say value
let me scroll this down a little bit so
you guys can see what's going on and
then we're just going to print these out
all right so that should work once I
actually put this down in our main
function here and we need a new file
name so we're gonna put this into a
different file here and then we are
going to simply say they have right
Jason
txt Jason then what we want to do is
there we go so will we run this assuming
it's all going to work
we'll get another whoops we'll get
another file out here actually go to our
directory here we'll get another file
out here called Jason dot txt and it
would contain our JSON object and then
if it returns true in the right where is
it right right here if that returns true
then right Jason will return true then
we'll actually read it back and then we
will go through this object and print it
out after we've decoded it from string
so this may seem a little complex but
this is actually a really good
real-world example this is really what
Jason is designed for is you would take
an object encode it down to a string
pump it across the network or Internet
or whatever and then your consumer as
it's called the consumer application
would take it read that string decode it
back into an object and then work with
it and boof that scared me it actually
did work the first time you can see we
have seven hello worlds and our people
object it contains Brian is 43 years old
and how there's 25 years old and sure
enough there's our JSON file and there
is our JSON object that got written down
to disk that was a mouthful and I'm glad
we didn't have any major errors because
I'm tired and I'm hungry so I'm gonna go
get some food but before I do that I
wanted to thank you guys for watching
and you can find the source code for
this and all of the tutorials out on my
website void roms comm just click on
github and then go out to all the
tutorials I got the flutter tutorials
here and then all the source code on top
of that feel free to visit the void
rooms Facebook group we have 1700 plus
and Counting programmers all different
languages I warn you right now most of
those animals love C++ you may get a
little flak if you post a flutter
question but actually everybody's pretty
decent in there so they'll probably help
you that's it thanks for watching
17th I better double-check that 17 yes
17 sitar his flutter got a little
frazzled err my phone was kind of
beeping in the background anyways we're
gonna continue on down our flutter
tutorials we're gonna learn a little bit
about IO
now when I say IO I don't mean the moon
Io I mean input/output and the first
part of input/output we're gonna work
with is called files and directories
files and directories is a huge topic
and we're gonna kind of condense it down
a little bit so obviously we can't cover
every single little use case but we're
going to cover the vast majority of them
we can't cover everything because we
will be here for 300 more videos you can
do just about anything with files you
can encrypt them decrypt a Minko time
decode them pump them across the network
scramble them up chop them up dice and I
mean whatever you want to do I sound
like an infomercial but files are quite
literally the bread and butter of most
programs so without further ado let's go
ahead and import dart convert dart IO
and let's work with this so first thing
we want to do here is let's say we want
to figure out how to list files and
directories in a path here so I say void
list if I actually did that correctly
and we first want to surround this with
a try-catch block
now why do we want to do a try-catch
block first it's because working with
the file system can be very error-prone
you ever worked with an older OS or a
computer that's kind of flaky you'll
know that really quickly that sometimes
files just do not play nice all right so
whoops well new alright so what we've
got here is we've got a directory object
and we're just going to make a new
directory object based off the path then
we're going to say now if you notice how
we can say exists and exists Inc this is
kind of the crux of the i/o portion of
dart io is asynchronous so what they've
done is they put some helper functions
in here that allow you to help you call
this synchronously so instead of doing
exists and then messing around with a
wait and then and you know futures and
all that we're just gonna do these sync
and let them do all the heavy lifting
for us so if it exists then where you
get file sensitive entity and we want to
list a sync then we're going to just
print out
so first thing we want to do here is
actually let's get a listing here so
we'll see we're just going to I'm on the
Linux system so just gonna grab the root
path users you might want to do that on
your C Drive let's just run this and see
what happens here you can see how we get
a whole list of things these are this is
everything that is on my root path here
if you've no Linux it's really nothing
special on this virtual machine
alright so whoops I got a positive eight
for one second here so how about that
somebody was at my front door so I had
to go see what it was all about we're
gonna change this path here and it's
just the path that I have the videos in
that way we're working with a very small
section of my file system so if I goof
up I'm not reinstalling my operating
system here although on Linux it's
really hard to actually blow something
up you can see how we actually have a
different structure now and this is
actually the movie that we're creating
at this very point in time so what we
want to do is we want to learn how to
write to a file
pool and this is just the way I do it
there's the problem with programming or
I should say the added bonus with
programming is there's literally
billions of ways you could do this I'm
just doing it my way if you don't like
it feel free to do it your way but this
is typically what I do when I'm writing
a program alright so we're going to do
the try catch block we did screw
something up up here
now if you're wondering why I'm doing
just a print to string it's because I
want to know when something actually
blows up the last thing you want is a
what's called a silent error which means
you have a catch and then you don't do
anything with it because then you run
your program and nothing happens and
you're like what the heck
so you want to know that there was
actually an error and that's why I just
print it out but all right so when you
say file so we're just saying want the
file object to be a new file based off
the path that we're giving it and I
probably should name this the path but
I'm just gonna leave it as file and then
we want to say a random access file I'm
gonna call this RF equal new random
access file actually nope sorry I
screwed up we want to get that off of
our file reference sorry about that and
we're going to say open sync now you'll
notice that there's open read open which
gives a future and then open write open
sync we're just going to work with open
sync there's different types of files
we're gonna work with what's called a
random access file meaning we can
randomly move around in that file and do
whatever we want with it
I typically work with random access
files because they're a lot more
flexible although they are a bit slower
technologies grown to the point that the
difference between a random access file
and say a sequential file is very
minimal and then we want to actually
give it a mode and the mode here is
going to be the mode that we give the
function or I'm sorry the method if
you're wondering what the mode actually
means you can actually say file mode
dot and see the different modes there's
a pen there's readers write write only
and write only app and append basically
takes an existing file if it exists if
it doesn't exist it creates it but let's
just say it exists and it just keeps
adding to the end of it think of it like
a line in the bank it'll just keep
adding to the end
read will read from the file write will
completely destroy the file and write it
from scratch think of writing as you
know you take your parent a bad report
card they wadded up into a ball throw
out the trash and say bring me another
write only means you can only write to
the file and write only append is pretty
self-explanatory
you can only append to the file why they
didn't call it append only I don't know
but all right so those are the different
modes and that's pretty standard of most
operating systems regardless of what
platform you're on that's kind of like a
file primer you probably spent a week
talking about that new computer science
class all right so what we want to do
now is we want to write string a sync
and we're going to just say data and
then we want to flush sync and we want
to close sync so flush and closed those
are real key words kind of ignore the
little sync at the end here for now SiC
just means that we are asking dart to do
this synchronously focus on flush and
close
what flush does is think of a file as
well like a toilet I hate to say it that
way but think of it like a toilet and
you're just dumping stuff into it and
when you're done you want to flush that
toilet write it down to the desk so
flush literally tells the operating
system hey write it down to the disk
closed then closes the file I am not
100% certain but I think under the hood
close may call flush for you I know on
some some different languages it
actually does I'm not sure if it does in
dart so I'm gonna call the flush
intentionally because that is what was
out in the actual code they had as an
example out here somewhere I'd have to
find it yeah right here writing file
contents I think they're doing this
because their example is asynchronous
and I'm doing it synchronously so I'm
not sure if I actually need to do the
flush I think I just need to close all
right so now that we know we can write
to a file we need to know how to read
from a file this is a little bit easier
and we're going to say a string and
we're gonna say read file
all right so we're going to just do our
try-catch block now for some of you
while I'm typing this out maybe reading
the comments out on YouTube there's a
lot of folks saying hey you know we
don't like these tutorials we want more
cute or qml or why are you using dart
and not cute and qml it's because I've
done a lot of other tutorials in another
language called C++ that uses a library
or I should say a bunch of libraries
called the cute I don't want to call too
cute framework because it's a cute
library but it's called cute and it is
kind of lost my train of thought here
hey it runs on any platform it's an
amazing system
I still love cute I still love qml and I
want to do more videos on that but right
now dart and flutter really have my
attention so that's just kind of my
focus and we're going to say
read as string sick now what we're doing
here is we're just saying create a new
file with the file name which creates
the file object now that we have the
file object F in this case we're saying
F read as string sync mean that's going
to read the contents of that entire file
into one giant string and then return a
variable we are then going to take that
variable and return it from this method
and what we're doing here is the default
encoding which is utf-8 which is an
entirely different conversation encoding
is how the actual information is written
and read to and from the disk in this
case we're going to leave it as utf-8
you can feel free to experiment and
change your encoding but just understand
that not all in codings are compatible
so we're just going to leave that as
default all right so now we have the
ability to write and the ability to read
let's test this out let's actually just
go here and we want to say we need to
make a another variable here hmm let's
call this let's call this txt file and
we're going to just say just give it a
very simple name or say if write file
and we need to give it our text file and
we need to say some sort of data that
we're going to write to we're going to
say and then the mode we're going to say
a patent and we're just gonna play
around with this for a little bit oops
so really what we're saying if this then
that so what's going on under the hood
assuming this works is we haven't
actually tested the code we're going to
write to our text file which is going to
be on this path in my virtual machine
and we're gonna write this data this
right here is called an escape character
and this right here is called an escape
sequence wow I misspelled world that's
embarrassing
so what escape does is it escapes out of
the character sequence and says I want
to put a special character in here slash
n stands for new return you can if
you're in a Windows machine I think it's
slash and / R or / r / and like that
actually it's the other way around I can
already tell by looking at its RN which
does a hard return a new line that's how
Windows does it but on Linux and Mac
it's just a new line you can also put
like a tab in there you can put special
characters you can put just anything you
want
we're just doing this to break it up so
they'll be in line we're doing that
because we're in append mode and we want
a new line every time we run this then
we're going to print and we're just
reading the contents of the text file
back that we just wrote and we should
see hello world down here when we run
this and you see bang hello world so if
we go out to our file system you see
that now there is a txt dot txt our test
dot txt and if we were to open this up
you can see there is hello world in
there now let's just move this off to
the side we run this again and you see
there's two now there's three now
there's four and you can see our text
files saying hey it's changed we're
going to reload it and that's a pen mode
it just going to keep going and going
and going now we're going to switch this
to write mode notice how we only have
one hello world and if we go back to our
text file reload it there's only one
that's the difference between write a
pen a pen is just going to keep adding
to it we're right it's going to
completely blow it away and start from
scratch I'm going to switch this back to
a pen because I want to put that up on
github the way it is
now let's say hmm we want to be able to
let me think about this for just a
moment here let's say we want to be able
to actually pump this out as JSON so
let's do that wasn't going to do it but
I'm like yeah why not people are gonna
ask how to do it so we're gonna say
before we do that I'm actually gonna do
something else
list sorry for being so scatterbrained
I'm kind of deviating from my original
plan here I'm trying to think in advance
of what people are going to ask for and
what they always ask for is okay it's
great that you can do it in one giant
blob how do you do it in a bunch of
lines you know how do you read lines
from a file so I'm just trying to limit
the number of questions that I'm gonna
get off of this thing and what we can do
here is we can just say very simply and
then we can just say
Red Lion sink and you can see how that
is currently going to return a list of
strings and it's that easy right there
we could just read the lines so let's
actually do that and let's comment this
out actually let's not let's say see
whenever I deviate from from the plan
here things happen very badly but that's
when we probably learn the most so let's
let's try this txt file so we want to
get the length of this let's run that
and you can see how there's two there's
three there's four there's five there's
six so there's six lines in that that
list object so that is how you would
read the individual lines and I'm
actually gonna comment this that was
embarrassing
Wow I really just spelled all of that
so what red lines does is it goes in and
it looks for that escape sequence of
slash on or /r or both and it actually
breaks those up into individual strings
so it's taken that giant string and
breaking it down into six individual
strings alright now we're going to go
ahead and we're going to read and write
some JSON here
so let's actually alright let's say pool
two let's say she's not to file I'm
having a hard time figuring out what I
want to call this there we go and it
will say string file now what we're
gonna do here is a little bit different
what we're gonna say is map and then we
want a string and an int we're just
going to basically plagiarize what we
did on our last tutorial here yeah I'm
getting hungry like just sitting here
something my stomach just starts
growling so I'm gonna put it absence and
we're gonna say Ryan yeah I've had a
couple people say what is cute what is
qml why are people getting upset that
you're not working on it that's why I've
just I've done like a I don't remember
how many I think like 150 hundred
seventy some of my videos a lot I've
done a lot of those videos and I've
gotten pretty advanced in that realm so
anytime I make something that's not cute
or qml everybody kind of wonders what
the heck is going on yeah I'm gonna get
back to it eventually I'm actually
hoping it back to it this winter alright
so we're going to say string Jason oops
strain data well Jason dot encode and
we're going to encode this map and then
we are going to return our right file
and we're going to say the file name our
data and then our mode we want this to
be file mode not right reason being if
we have a pen will have multiple JSON
objects in there and it'll probably
crash the program or it will just get
garbage back or we won't get the latest
object something bad will happen all
right so we've got JSON to file actually
let's call this write JSON there that's
better now I'm happy with it now we're
gonna say void we're gonna read the JSON
I fought JSON for a long long time I was
really into XML I did not like Jason
when it first came out XML is just been
around forever but it's horribly
inefficient
all right string data equal and we want
to actually read the file so we're just
reusing the code that we wrote so rather
than reinvent the wheel with the right
file and read file we're just reusing
our functions here now we need to do a
little bit of error handling here you
notice how right JSON is just returning
the value of right file now with this we
can't do that so what we need to do is
say if data that is empty then we're
gonna say print no data
and then we're just going to return out
of this function and we should also get
the error string from the actual right
here in the actual method all right now
now that we know that we have data
because at this point we should have
data I say map
string int this is the structure of our
map here structure of our map that
really didn't make a whole lot of sense
but I think you guys knew what I meant
all right so we're gonna say people
equal Jason D code and we're just going
to decode that data into an actual
object and then from there we're going
to say print we want to know what the
people object contains just so that we
can prove that we actually decoded this
we're going to say people not for each
and then we're going to say value
let me scroll this down a little bit so
you guys can see what's going on and
then we're just going to print these out
all right so that should work once I
actually put this down in our main
function here and we need a new file
name so we're gonna put this into a
different file here and then we are
going to simply say they have right
Jason
txt Jason then what we want to do is
there we go so will we run this assuming
it's all going to work
we'll get another whoops we'll get
another file out here actually go to our
directory here we'll get another file
out here called Jason dot txt and it
would contain our JSON object and then
if it returns true in the right where is
it right right here if that returns true
then right Jason will return true then
we'll actually read it back and then we
will go through this object and print it
out after we've decoded it from string
so this may seem a little complex but
this is actually a really good
real-world example this is really what
Jason is designed for is you would take
an object encode it down to a string
pump it across the network or Internet
or whatever and then your consumer as
it's called the consumer application
would take it read that string decode it
back into an object and then work with
it and boof that scared me it actually
did work the first time you can see we
have seven hello worlds and our people
object it contains Brian is 43 years old
and how there's 25 years old and sure
enough there's our JSON file and there
is our JSON object that got written down
to disk that was a mouthful and I'm glad
we didn't have any major errors because
I'm tired and I'm hungry so I'm gonna go
get some food but before I do that I
wanted to thank you guys for watching
and you can find the source code for
this and all of the tutorials out on my
website void roms comm just click on
github and then go out to all the
tutorials I got the flutter tutorials
here and then all the source code on top
of that feel free to visit the void
rooms Facebook group we have 1700 plus
and Counting programmers all different
languages I warn you right now most of
those animals love C++ you may get a
little flak if you post a flutter
question but actually everybody's pretty
decent in there so they'll probably help
you that's it thanks for watching
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Nov 22, 2024 Last updated |
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