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To connect to an API using Retrofit we create an interface that describes the endpoints. These methods describe the HTTP method we are using, URL we are calling to, and the type of data we expect to receive back.
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Welcome back, we added the functionality
to authorize the user and
0:00
allow our app to act on behalf of them.
0:04
So next we need to add the functionality
to connect to the imager api and
0:07
get the user's currently uploaded images.
0:11
And this is where we're
start leveraging retrofit.
0:15
So to connect to an api using retrofit,
we want to create an interface.
0:18
And that interface is going to describe
the endpoints we're connecting to.
0:23
So here I already have
our imager interface, and
0:27
we're going to start adding to it.
0:30
So in here I'm actually gonna make
sub-interfaces within this one and
0:34
that's because some of these endpoints
we connect to are gonna require
0:37
authentication, some of them aren't, so
we want to distinguish between those two.
0:41
So here I'm gonna say interface and
I'm just gonna call it auth
0:44
because these are gonna be the endpoints
we connect to that require authentication.
0:48
And next we wanna go ahead and
add the method for
0:53
getting the users uploaded pictures.
0:57
Here's what that looks like.
1:01
First we can annotate the type
that this is gonna be.
1:03
It's going to be an HTTP GET call.
1:06
So we annotate get.
1:10
Notice it's prompting us to import here.
1:12
We're gonna go ahead and do that.
1:15
Then we're going to add in
the end point that we connect to.
1:20
And this is found in the documentation
on the Imgur API website.
1:24
The version is three of their API.
1:30
You want to connect to the account.
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And we're going to put in the user name.
1:35
Get the images for that account.
1:40
And optionally page through various pages
1:43
of images if they have a lot of images
uploaded there's gonna be pages of them.
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The method actually looks
like this has a name.
1:52
We're gonna call images and
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text we fill in those path
variables user name and page.
1:58
We're going to supply
an annotated path parameter here,
2:01
and we just want that to match
the names that we gave them in the URL.
2:07
And this is going to be a string.
2:12
The second one Is the page number.
2:13
That's gonna be an int.
2:22
Okay, but we need to make sure
that we import these as well.
2:25
And finally we need to
add the return type.
2:31
So on retrofit the return
type is always a call.
2:33
You can see here that
it's parameterized and
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the type we're expecting to get back is
something called BassicArrayList=Image.
2:43
And we're gonna wanna use the image class
that's in the model that I've supplied.
2:56
Let's go ahead and
take a look at what basic actually is.
3:06
So if we look here in our model we can
see that basic is a really simple class.
3:10
It has a status code, and
a bullion indicating whether this call is
3:15
successful, and then it has some
data associated with it and
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this is parameterized as well so the type
of data is whatever you supply to it.
3:23
In this case, I know that I want to
get back an ArrayList of images.
3:28
And we can look at the image class.
3:33
It's also pretty straightforward.
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It's just all the metadata that each
image has when it's returned back from
3:37
the imager API So looking back here, we
can see we have a complete API call now.
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Okay since this is an interface, it's
not an actual object we can work with.
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We need something to create an object
out of this interface declaration.
3:54
And that is something that
we usually call a service.
4:00
You can call it anything you want.
4:03
But typically will create
a class called service.
4:05
And we're going to use this to create
instances of our API that we can use.
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So it's going create a new class and
our API.
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We'll call it service.
4:14
And what we want to do here is
how to method that returns back
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an instance of our.
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API interface that we just created.
4:26
So let's go ahead and
create a new method and static, and
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it's going to turn back
the type that we just created.
4:33
And we'll call it getAuthedApi.
4:39
And the nice thing
4:40
about retrofit is that it has really nice
builder classes built right into it.
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So here we can say return
new retrofit.builder.
4:50
Let's go ahead and import that.
4:55
And the first thing I wanna
supply is the base URL and
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we stored that earlier in our image or
a class.
5:07
We wanna add a converter factory.
5:12
So this is what's actually used
to take the binary data and
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convert it into some object
type that we can actually use.
5:18
Those are the models,
image that we have in our model package.
5:22
So the one we included
in our dependencies,
5:27
if your member earlier, is the JSON one.
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JSON has JsonConverterFactory.create.
5:33
And this creates an instance
of this converter for us.
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Finally we call, build.
5:41
And then we're gonna call create.
5:43
And in create, what we're going to do
is pass in what we want to create.
5:48
Which is an instance of
our Imgur.Auth.class.
5:55
So this is gonna to return back
an instance of our Imgur.Auth.class.
5:58
Now there's one thing we do need
to add here, and that is because
6:06
in the documentation found on the website
it says, for every request, if
6:11
we're authorized by the user, we need to
include the access token in that request.
6:17
And the way we do that is we
add a header to that request.
6:22
So the way we're gonna do that,
it's pretty easy, pretty straightforward.
6:26
First we're gonna get our HTTP client.
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It's the OK HTTP client.
6:34
And we're going to supply
a custom OK HTTP client.
6:35
We're gonna use the builder and with
the builder are gonna say add interceptor.
6:40
And here's what this is gonna do.
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Every single call that goes through
this instance of OkHttpClient will
6:49
be intercepted by this piece
of code we're about to write.
6:54
And so for every single request that comes
in, we're just going to take that and
6:57
append a new header with our
access token and let it proceed.
7:01
So create a new interceptor.
7:07
And you can see here the call
that happens is called intercept.
7:09
And when it calls
intercept has this chain.
7:16
So there can be multiple interceptors.
7:19
Happening at different
levels of the request and so
7:22
what we're going to do is we're
going to call chain.request and
7:25
this is going to give us
back the current request.
7:28
I wanna call it authed
let's import this and
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the request is now going to be added to.
7:41
And to do that, I can use a newBuilder.
7:49
And with newBuilder, it allows me to
build on to the existing request.
7:52
So I'm gonna say, newBuilder addHeader.
7:56
And the header is authorization.
8:00
And the format looks like this,
bare space.
8:05
And we want to add in our token.
8:13
So I'm going to call get access to it.
8:15
Finally We can build this, and
8:23
this is gonna return back
a new request that is off.
8:27
That is it has an authorization
header we've added to it.
8:31
Finally from this we have to
return back a response, and
8:34
that is done by saying
return chain.proceed.
8:37
And this will proceed
to send our new request
8:41
on to the next level in
the network request.
8:44
And here, instead of ending it,
we're going to call build,
8:52
cuz we were working with
the OkHttpBuilder here.
8:56
So call build here.
9:00
That returns back the actual client.
9:02
And one final thing is we need to supply
this client in our retrofit builder so
9:05
that it's used every
time we make a call here.
9:10
So here, we're just gonna call client,
and supply it.
9:13
So this is gonna complete our Service
class and the getAuth API method,
9:19
which will return back an instance
of the interface Imgur.auth.
9:25
Okay, so we've written some code.
9:29
Uses OK HTTP client,
it uses retrofit builders.
9:33
So, you might be wondering what's
the difference between all this?
9:38
What's retrofit, what isn't?
9:41
Let's go ahead to talk about
the differences between HTTP,
9:43
OK HTTP and retrofit.
9:48
So, http, it's a standard
protocol used by all web sites to
9:50
deliver content between different clients.
9:55
So it has things like the type.
9:58
Here we have to get it's using HTTP
2.0 and it has the host this is
10:01
the API we're connecting to and that
typically has a whole bunch of headers.
10:06
So these have a lot of different
information used by clients to know
10:12
what data is coming over the wire.
10:16
Then there's going to be some response.
10:20
That might be a 200, that means it's okay.
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That's a standard value.
10:25
Again, this is just a protocol being used,
in addition to this the response might
10:28
have a number of headers as well,
just like the request had.
10:32
The response will have additional headers.
10:36
And finally, the response is
going to have the actual data
10:39
that it's responding with,
so in this case, some Json.
10:43
And we can see here.
10:47
It has an id, a title, a description.
10:49
This is just an example.
10:52
Typically a response is much longer,
has much more data involved.
10:53
So that's HTTP.
10:57
So what is oKHTTP?
11:00
OkHttp Is an HTTP stack that allows us
to make HTTP calls using HTTP easily.
11:02
We can create a URL like this
by just making a string.
11:10
We can create a new client and
then create a new request using a builder.
11:14
Here I call get.
11:20
It's a get request, supply the URL.
11:21
I can add headers and
call build to build a request.
11:23
And then I can say newCall.
11:26
And that's gonna give me
back this call object.
11:27
And then I would do something like this.
11:31
I would say call.enqueue.
11:34
This is going to enqueue this
call in a threading pool.
11:36
So it's going to execute off the main u.i.
11:41
thread.
11:42
And i'm going to get a callback so
i supplied a callback here.
11:43
You can see I have a response and
a failure.
11:46
So if i get it back it's a two
hundred that means okay.
11:49
I'll get my response call.
11:52
If something happens and this fails,
I'm gonna get it an on failure call.
11:55
So that's OkHTTP,
11:59
it wraps up it’s to be a protocol
in some nice builders and
12:03
easiest classes, then there's retrofit.
12:07
Retrofit adds another level of easy
syntax to use on top of OkHTTP.
12:12
So we can see here, instead of having
to type .get, we can actually annotate
12:19
the URL and dynamic path variables and
the type, all in one go.
12:23
We can also easily tell it what type
of data we expect to get back and
12:30
it does the converting,
using that converter factory we supply.
12:34
And then we can just create a simple,
small piece of code using the retrofit
12:39
builder to tell it, all right what
is the API URL we're connecting to?
12:44
Do we need to supply a custom client?
12:47
Which we did.
12:49
And it creates an instance
of that class for us.
12:51
So it takes that interface, creates
an instance object that we can easily use.
12:56
Finally it does return back a call
the same type of call that HTTP has and
13:03
again, we can enqueue it.
13:08
But the difference here is
that we can use this nice,
13:10
static method we built in our service
class to do something like this.
13:13
We can say Service.getAuthedApi.images,
enqueue, and
13:17
just put our callback right there.
13:21
So this is something that we're gonna add
to our activity to actually call this.
13:23
And then the callback is gonna
happen in our activity so
13:28
we can display the images
that come back in the UI.
13:31
And again you'll notice we get
the onResponse, and we get the failure.
13:35
So we know what's happening and
we can respond accordingly in our UI.
13:39
Here we're back in our main activity and
now we want to actually add the call to
13:45
the API that we created in
our Imgur API interface.
13:48
So here we can see that in on create
we check if are authorized and if so
13:54
we call this show account images so
let's go and go to that definition.
13:59
You can see here that first we're just
going to show the images container and
14:03
hide the sign in
an anonymous upload buttons.
14:08
And the first thing we need to do here
is our to do which is to actually
14:12
make this call.
14:15
So let's go ahead and we'll add a call to
another method called fetchAccountImages.
14:16
And then let's go down and define that.
14:24
Okay, so we're gonna use our service
class that we created before.
14:33
Service.getAuthedApi.images.
14:39
And the first thing we need to supply
is that user name so let's go ahead and
14:46
use their off util to retrieve that back.
14:50
And the second thing is the page number.
14:57
For now let's just go ahead and
use page zero.
14:59
That's going to be a very first page.
15:02
So this is going to return
back a hold command.
15:05
Hover over here,
it's gonna return back our call.
15:09
And then we want to enqueue our call and
provide the callback.
15:12
So we'll say new callback and go ahead and
do what it suggests us to do,
15:17
which is provide an implementation
with the type correct.
15:23
It's gonna return back
our array list of images.
15:27
So, onResponse is gonna get called
as long as the HTTP call succeeded,
15:31
went through and
connected to the API and came back.
15:36
So, it may come back and it failed
in some way, according to the API.
15:40
The request didn't fail coming back,
15:44
but the API maybe didn't like
our request in some way.
15:45
So the first thing we want to do is
just check that our response.code
15:49
equals a known value which is OK.
15:56
That's the two hundred value.
16:01
And so as long as it's OK we
know that We got data back.
16:03
That's what we wanted.
16:08
So if we do have data back,
what we want to swap that in for
16:09
the adapter that's set on
the recycler view in this activity.
16:13
So I've already set that
up in the starter files.
16:18
So first thing I'm gonna do is just
cast to the type ImageAdapter and
16:21
get our adapter from the recycler view.
16:25
And then I'm gonna call
the method on it swap.
16:30
And I want to swap in the new data.
16:32
Notice that the data is
already in the type I need it.
16:36
That's because retrofit
converts the binary data
16:39
into the type that I
need using the converter.
16:42
So here I can just say
response.body().data.
16:45
That's gonna swap out these new
images into a recycler review.
16:51
Now if something went wrong if there
was something else that was a problem,
16:57
let's go ahead and
indicate that in some way.
17:00
I'm going to make a little snack bar.
17:03
You probably wanna have some sort
of prompt or make sure we go into
17:05
a state to allow the user to retry this or
maybe retry yourself a few times.
17:10
But for now I'm just going to go ahead and
supply a snack bar to just indicate
17:15
visually in the UI if
something went wrong.
17:20
I'm gonna say Failed and
provide a little sad face.
17:28
Finally, don't forget to call show and
17:35
I'm going to do the same thing
if a failure case happens.
17:38
So, a failure would
call back to onFailure,
17:43
if the call was unable
to complete in some way.
17:48
So if the call does complete in some
fashion, maybe the code's wrong or
17:51
we requested something incorrectly.
17:56
But it does complete.
17:58
It'll come back to onResponse.
17:59
If it fails in some way
18:01
trying to transmit the data over the wire
it's gonna come back to onFailure.
18:03
Now finally it's important to note
that when we call enqueue and
18:08
we provide this callback, this is
going to happen on the main UI thread.
18:12
The call itself will happen on
another thread, which is what we want.
18:16
But we can interact here, for instance,
18:20
with our adapter because
we are on the UI thread.
18:22
One more quick thing we're gonna do is
just add in another snack bar to tell us
18:26
that we're getting the user's images.
18:29
So we'll say Getting Images for
Account and
18:34
that'll just provide a nice UI so
we can know when this request starts.
18:41
Ok let's go and run this and
see this in action.
18:47
What we should see is that when
we run it we're not authorized.
18:51
We're going to need to authorize our app,
get a call back into our app, and
18:54
then make this call to
fetch image accounts.
18:58
And when we come back up here
what we'll seen on resume is that
19:02
If it is authorize show account
images should be called.
19:05
And that will in turn call
fetch account images and
19:09
we should get those images
displayed back to us.
19:12
So let's go to run this.
19:14
And run this on our device
switch over to our device now.
19:21
And our app just started.
19:36
First thing we'll see is
we have the sign in button.
19:37
The upload anonymous image button,
we'll get back to that later.
19:39
First thing we want to do
is we want to sign in and
19:43
authorized user and
authenticate our app for the user.
19:44
Go ahead and click sign in.
19:49
Remember this can take us to the image or
API website where we need to log in.
19:51
So here log in with your account and
click allow.
19:56
I'm gonna go ahead and
log in with mine now.
19:59
Okay, so once user signs in it's
gonna open this prompt with the url
20:06
that's coming back to our apps so we wanna
go ahead and use our Retrofit workshop.
20:11
And you can either say just once or
always.
20:17
For me i'm just gonna say always.
20:21
Here you can see it said we
are getting images for this account.
20:28
And lo and behold the images appeared.
20:32
So our API call succeeded.
20:34
And we got the images.
20:37
So this looks pretty great.
20:40
In the next video, we're going to go
ahead and fill out the functionality for
20:42
this bottom Upload Image button.
20:46
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