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. 1:32 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. 1:47 The method actually looks like this has a name. 1:52 We're gonna call images and 1:54 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 2:38 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 3:19 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. 3:35 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. 3:41 Okay since this is an interface, it's not an actual object we can work with. 3:49 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. 4:07 So it's going create a new class and our API. 4:12 We'll call it service. 4:14 And what we want to do here is how to method that returns back 4:22 an instance of our. 4:25 API interface that we just created. 4:26 So let's go ahead and create a new method and static, and 4:29 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. 4:45 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 5:02 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 5:15 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. 5:29 JSON has JsonConverterFactory.create. 5:33 And this creates an instance of this converter for us. 5:37 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. 6:31 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. 6:47 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 7:34 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. 10:23 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