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Add some final polish by saving state across rotation and displaying loading and error states.
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Now we need to actually
perform our API call.
0:00
You don't have a method to actually do
that from our Etsy class yet so let's go
0:03
ahead and add in a new method to Etsy
class so we can perform a call to our API.
0:07
This method needs to be public so that
the activity class has access to it and
0:13
can call it.
0:17
Now the important thing
is that this is void.
0:20
We're just going to be
passing in the call back.
0:22
So the call back is going to get
called back when the network request
0:25
completes and
is parsed into the active listings.
0:29
I'm gonna call this getActiveListings.
0:34
And it's going to take in
the callback of type active listings.
0:37
And what we're going to do is,
oh, import callback type,
0:42
what we're going to do is just call API,
and the API has our active listings.
0:47
And to call that we need
to include images and shop.
0:54
And it's asking for
the call back itself, which is here, so
0:58
now that, since this is public,
we can call it from our main activity.
1:02
First what we need to do is
set up our recycler view.
1:08
To do this we need to set a layout
manager on our recycler view, and
1:14
in this case, I'm just going to use
a staggered grid layout manager.
1:18
And it's going to take number
of spans that we want.
1:23
For now, I'll just say one.
1:26
And it wants an orientation, which just
going to say vertical to start out with.
1:27
You might want to change the span
count to be based on a dimension or
1:35
integer, based on the number columns
that might fit on the screen.
1:39
You can choose whatever you want.
1:43
I'm just going to go ahead and
go with one for now.
1:45
And our list is going to be scrolling hor,
vertically up and down.
1:47
So we've chosen vertical.
1:51
Next, we need to go ahead and
set an adapter on here.
1:54
I'm going to say new listing adapter.
1:56
We need a pass and a context,
which is this referring to the activity.
2:02
And we need, actually,
2:07
to use this adapter because remember
this adapter is our call back.
2:08
So, let's go ahead and
take this adapter object, and
2:12
get that reference before we assign it.
2:16
And then what we're going to do
is first time we're running,
2:23
saved instance state will be null.
2:28
We can go ahead and
just fire off the API call.
2:29
We're going to pass in the adapter.
2:34
Okay.
This looks pretty great.
2:37
We need to go ahead and
save state as well.
2:39
So let's override the on
save instance state method,
2:42
and in on save instance state,
2:48
we need to save the data
that came back from the API,
2:51
so I'm going to keep the key for
the save instance state.
2:56
If savedInstanceState was null, it was the
first time, we're going to go ahead, and
3:10
again, and show loading.
3:14
If it wasn't null, we need to go ahead and
pull out from savedInstanceState.
3:18
The parsable object,
which is our active listings and
3:25
on our adapter,
we need to call success with that data.
3:32
The data is the parsable object.
3:44
Which is in fact active listings, object.
3:45
And the second value of success
is the response itself.
3:51
Which we can just pass in null.
3:59
So now, if it's the first time running,
we're going to go ahead and show loading,
4:03
we're going to make the call to
the network, otherwise when we come back,
4:07
if we have that active listings there,
we're going to just go ahead and
4:10
set it on the adapter and
display our lists.
4:15
But it might be the case that we don't
have any data yet, so we need to make sure
4:20
we check if there's any data to begin
with in the saved instance state.
4:24
So we're gonna only do this if the saved
instance state contains the key.
4:27
So if it contains that key
that means it had some data.
4:35
And it, on saving some state, we're gonna
go ahead and check by getting that data.
4:39
Now we need to add a method to our
adapter to get the current data, so
4:45
let's go ahead and add that in here.
4:49
Public, it's gonna return back
that active listings object,
4:53
getActiveListings, and we're just gonna
return our active listings object.
4:58
It may or may not be null,
it could be null.
5:03
So, we need to check that.
5:06
Now we have to have access to our
adapter here so, let's go ahead and
5:08
move the scope of this to be just
within our activity class itself.
5:13
So, if the active listings are not null,
we're gonna to go ahead and
5:31
put them in our outState window.
5:34
Put parsable, going to give it the key,
and the actual active listings object.
5:38
So if we have that data, it'll be
passed into the bundle, the outstate.
5:44
Then come back to on create.
5:49
We're going to check if there's data.
5:52
Go ahead and display it.
5:54
If not, kick off a call to the API.
5:55
So in this case, again there was an eta,
it wasn't stored in the save instance
5:59
state bundle, so again we need to show
loading, and do another call to the API.
6:04
One last thing we want to do is in
our adapter, we want to go ahead and
6:15
if failure does happen,
we want to call back to our activity and
6:19
say we should display that error text.
6:22
So, since that's the case,
we need access to that activity.
6:25
So, instead of passing in
a generic context here,
6:28
let's just pass in our
main activity itself.
6:31
And we'll just call this activity instead.
6:35
And we'll keep a reference
to it here in the class.
6:40
And then down on success.
6:53
We're gonna go ahead and show the list by
calling to our activity show the list.
6:58
Otherwise, you wanna show that failure.
7:05
So it's gonna show the error message here.
7:11
And error message we can actually
retrieve from our object here.
7:14
Okay, let's go ahead and run this to
see if everything is working okay,
7:18
we should get a call to the network, get
a response back, display some listings.
7:21
Our app now displays listings from an API.
7:30
We use the Retrofit library to
make it easy to call the API and
7:34
parse the response to the type we need.
7:37
After that, we displayed
the list using Recycler view and
7:40
the staggered grid layout manager.
7:43
Finally, in our adapter, we used
the Picasso library to display the images.
7:46
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