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Retrofit makes performing Http calls easy by having a concise easy-to-read syntax, straight-forward integration to a project, and supporting the Android threading model as a default.
Resources:
Imgur API
Retrofit Documentation
Check out the 'Downloads' tab for this workshop's Project Files
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[MUSIC]
0:00
Hi, my name is Jamie Huson and
I'm an Android Developer at Etsy.
0:04
In this workshop, we're going to integrate
the Retrofit library from Square into
0:09
an app to show how easy
working with an API can be.
0:13
Retrofit makes performing HTTP
calls easy by having a concise,
0:17
easy to read syntax, straightforward
integration to a project, and support for
0:21
the Android Freddie model as a default.
0:26
Let's break down how it does this.
0:30
Retrofit consists of four parts.
0:32
An interface that declares the end points,
0:34
their HTTP types,
callback types, and parameters.
0:37
The methods are annotated making it
easy to configure an endpoint without
0:41
much code at all.
0:45
Here's an example of
a basic HTTP get call.
0:47
Next, is the adapter.
0:50
The adapter transforms your interface into
an object instance you can work with.
0:52
An adapter can be configured with
additional information about your
0:58
HTTP stack.
1:01
A converter will be used to
convert the returned binary data
1:02
into a java object you can easily use.
1:06
Finally, a call and callback mechanism,
to have fine grained control over when and
1:09
how requests are executed.
1:14
In this app, we're going to connect to the
image or API, we'll be able to anonymously
1:18
upload images or sign in for a user and
upload images to their account.
1:22
I've supplied starter project files for
you, you can import these to
1:27
Android Studio or create your own new
project and drop the files in yourself.
1:31
Here I've got the start
files open in a project.
1:36
So let's check out what I gave you.
1:39
First thing we're gonna look at is
our build.gradle file for our app,
1:42
let's go ahead and open that.
1:45
And what you'll see here is that near the
bottom, I've added some dependencies for
1:48
us already and that includes
the most important one, retrofit,
1:52
what we're gonna be learning today.
1:56
And also the second part of that is
the retrofit converter using gson.
1:58
So it's important that your code
matches exactly what I'm doing here, so
2:04
make sure you use the same version as me.
2:07
You can upgrade to a more
recent version but
2:10
there may be changes in
how the code is written.
2:13
You can also see if
supplied the main activity,
2:15
base application an adapter for a list.
2:18
This classical o op util, we'll go back to
that later, and some model classes here.
2:22
Next we need to look at
the documentation for
2:28
the API we're connecting to,
in this case imager.
2:30
Let's go ahead and go to the browser and
go to their documentation site for
2:34
their API, it's api.imgur.com.
2:37
And if you don't have an account with
a Imgur, go ahead and create one.
2:41
And then, what we're going to do is
we're going to go up to our account,
2:44
in the upper right, and go to settings.
2:47
What we're going to look
at is applications.
2:50
So I've created an application here if
you haven't created one, go ahead and
2:54
create one now.
2:58
And what you'll see is that it has
a name of called mine Retrofit Test,
2:58
you can call it whatever you want and
a client ID, that's really important we're
3:03
gonna need that we don't need the secret
but we do need this thing called redirect.
3:07
So you can see here if I
click edit what mine is,
3:12
it's https://treehouseworkshop:88.
3:15
:88 is a port, so
enter yours something like this.
3:19
If you're not sure, just put exactly
what you see here on the screen.
3:25
Okay, so once we have all those
applications set up with the API
3:31
what we're going to do is we need
to authorize our app to work for
3:35
users, that will allow us to
upload images to their account.
3:39
So to do this what we're going to do
is use something called oauth and
3:43
this has a flow to it.
3:47
And it's described here in
the documentation in detail under
3:48
authentication and
oauth 2.0 you can read more about that but
3:54
the just of it is this we're gonna direct
the user to a URL in the browser and
3:58
in that URL we're going
to put our client ID.
4:03
Then the user is going to sign in and
the browser will redirect to another URL,
4:07
that's our redirect URL we just
supplied in the application settings.
4:12
So our apps can intercept that URL and
direct users back into our out.
4:16
And then we're gonna parse out
4:20
some really important information
on how to connect to image or API.
4:23
The most important one is the access
token that it provides for us.
4:27
So to begin, let's go ahead and create a
place in our code base to store all these
4:32
constants that we need to know about for
connecting to this API,
4:36
all this information, is found here
in the API documentation, and so
4:40
if you have any questions you can
come back, read through this,
4:44
and look it up they're
switching to the code base.
4:47
Okay so the first thing we wanna do is we
wanna create a place to store what URL
4:55
we're gonna be connecting to.
4:59
So in our API let's go ahead and
create a new Java class let me call it
5:02
Imager and it's actually not going to be
just a class I want to be an interface.
5:09
And in here, we're going to go and
5:17
store the basic information
about connecting to images API..
5:18
It's pretty string we'll call
it an imgur or base URL,
5:22
and this is the base your ID,
connect to their API.
5:28
Okay, the next thing we need to do
is we need to store that client ID,
5:37
we're going to use that to connect.
5:41
So you wanna go ahead and
go to the web site again, go
5:45
to your account settings, go to your
applications, and copy in that ID.
5:51
And then we're going
5:57
to create this URL that
6:02
has our client ID in it, and
this is what that URL looks like.
6:07
Again, it's documented
in the documentation,
6:13
you can read about it there.
6:15
This is what it looks like,
I'm gonna call it AUTHORIZATION_URL.
6:17
And it looks like this.
6:21
API, and then oauth2, authorize and
6:23
one of the parameters we need
6:30
to include is the client ID.
6:35
So, it's client_id and then I'm just
going to append client ID to it.
6:40
And then this ends with a final type,
6:47
which is what we want
to get back from this.
6:52
What we want to get back is a token,
so let's go ahead and tell it that.
6:54
Response type is the parameter,
we just want to say, we want a token back.
7:03
Okay, finally let's go ahead and
store that redirect URL.
7:09
Next, we need to add in something to our
manifest and this is what's gonna allow
7:27
us to redirect the user back to
our app once they've signed in and
7:32
gone through the authorization
process on the imagur website.
7:36
It's going to open up our manifest and
7:40
scroll down, and you can see
this block is really important.
7:44
I've already put it in there for you but
7:51
it's important that you
know this is in there.
7:52
So what we're saying is that if we're
going to VIEW this URL, starts with https,
7:55
treehouseworkshop, the port is 88,
then we want to go back into our app.
8:02
So if you don't have this in
there this isn't going to work so
8:07
make sure that this is
included in your project.
8:11
If you use my starter files
it's already in there.
8:13
Okay, now let's place all
the information we get back from the API
8:18
into a shared preference object.
8:23
So the API is gonna give us back this
token, and we want to be able to store
8:25
that so that we can make requests
every time the user starts the app.
8:29
So let's go out and
put in a shared preference.
8:33
And I've started that already using this
oauth2 class, so let's open that up.
8:35
We can see here I have
added some todos for you.
8:40
Need to put the constants in the top,
let's go ahead and
8:44
start doing that right here.
8:47
So again these represent all
the data we're going to get back
8:51
from the imager API,
we're gonna get back an access token.
8:55
Gonna get back a value called expires_in,
9:04
this tells us how many milliseconds
our access token is valid for
9:08
before it expires and
we need to authorize the app again.
9:13
We're gonna get the type or
the token type specifically.
9:23
And we're gonna get something
called the refresh token.
9:33
This is what you use once your token
has expired to get a new token.
9:38
And finally something that's going to get
9:47
passed to us is the username of
the account that we're accessing.
9:50
Okay, so what you'll see is
that I'm keeping a singleton
10:01
of the shared preference in this class.
10:04
And I wrote a little TODO here,
in case you're not using my starter files.
10:07
In your base application,
make sure you call init here,
10:11
this creates a new instance.
10:14
So there are some getters and setters for
storing data into the shared preference.
10:21
And the last thing we need to do here
is we need to complete the logic for
10:26
this helper called isAuthorized.
10:30
So isAuthorized is going to tell us
do we have a valid token or not, so
10:32
to compute whether we have a valid token,
what we need to do is return.
10:37
If we have an access token at all,
so that should be not null.
10:46
And we want to make sure that
the expires in value is still valid,
10:53
so let's call getLong and
get the EXPIRES_IN value.
10:59
And make sure that that's less than
the current time on the system.
11:03
So if both these cases are true, then we
have a valid token and we're authorized.
11:10
That's good for now, when you come back
we'll authenticate our app for the user.
11:16
Now that we know about how Retrofit works,
let's start writing our app.
11:22
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