Kotlin: How to fetch data from web service and display it in app? - api

Question

Hello :) I'm working on app that shows popular movies and some details about each of them. I created a RecyclerView where information should be displayed. I'm stuck with getting and displaying data. I'm using https://www.themoviedb.org/ page for api.
I was following these steps: http://imakeanapp.com/make-a-movies-app-using-tmdb-api-part-4-networking-using-retrofit-library/ , but it's written in Java and I need code in Kotlin. I converted by myself a part of the code, here is what I have:
in Movie.kt
data class Movie (
#SerializedName("id") val id: Int,
#SerializedName("title") val title: String,
#SerializedName("poster_path") val posterPath: String,
#SerializedName("release_date") val releaseDate: String,
#SerializedName("vote_average") val rating: Float
)
in MoviesResponse.kt
data class MoviesResponse (
#SerializedName("page") val page: Int,
#SerializedName("total_results") val totalResults: Int,
#SerializedName("results") val movies: List<Movie>,
#SerializedName("total_pages") val totalPages: Int
)
in TMDbApi.kt
interface TMDbApi {
#GET("movie/popular")
fun getPopularMovies (
#Query("api_key") apiKey: String,
#Query("language") language: String,
#Query("page") page: Int
): Call<List<MoviesResponse>>
}
in OnGetMoviesCallback.kt
interface OnGetMoviesCallback {
fun onSuccess(movies: List<Movie>)
fun onError()
}
in MainAdapter.kt
class MainAdapter: RecyclerView.Adapter<CustomHolder>(){
var movies: List<Movie> = listOf()
fun MainAdapter(movies: List<Movie>) {
this.movies = movies
}
override fun getItemCount(): Int {
return movies.size
}
override fun onBindViewHolder(holder: CustomHolder, position: Int) {
holder.bind(movies.get(position))
holder?.setOnClick()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomHolder {
val layoutInflater = LayoutInflater.from(parent?.context)
val cellForRow = layoutInflater.inflate(R.layout.movie_row, parent, false)
return CustomHolder(cellForRow)
}
}
class CustomHolder(view: View): RecyclerView.ViewHolder(view){
fun bind(result: Movie){
itemView.title.text = result.title
itemView.release_date.text = result.releaseDate
}
}
in MoviesRepository.kt
val BASE_URL: String = "https://api.themoviedb.org/3/"
val LANGUAGE: String = "en-US"
data class MoviesRepository (
val repositroy: MoviesRepository,
val api: TMDbApi
)
object getInstance{
val retrofit: TMDbApi = Retrofit.Builder()
.addConverterFactory(GsonConverterFactory.create())
.client(OkHttpClient().newBuilder().build())
.baseUrl(BASE_URL)
.build()
.create(TMDbApi::class.java)
}
in AllMoviesActivity.kt
class AllMoviesActivity : AppCompatActivity(), Callback<List<MoviesResponse>> {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_all_movies)
rw_main.layoutManager = LinearLayoutManager(this)
rw_main.adapter = MainAdapter()
getMovies()
}
private fun getMovies() {
getInstance.retrofit.getPopularMovies("2B0b0e8d104f0d6130a4fc67848f89e107", LANGUAGE, 1).enqueue(this)
}
override fun onResponse(call: retrofit2.Call<List<MoviesResponse>>, response: Response<List<MoviesResponse>>) {
val moviesResponse = response.body() ?: listOf()
Log.d("Results", moviesResponse.toString())
}
override fun onFailure(call: retrofit2.Call<List<MoviesResponse>>, t: Throwable) {
Toast.makeText(this, "Failed", Toast.LENGTH_SHORT).show()
}
}
And I have added in Manifest file Internet permission. When I run this, I get 'Failed' Toast and I don't see RecyclerView. Can you tell me what I'm missing or what's wrong? I've been searching on the Internet solutions but with no results. Hope you could help me. Thanks!

Answer 1

Looks like you are missing something small. After making a call to the API on Postman, Here's what you expect on your response body:
{
"page": 1,
"total_results": 10000,
"total_pages": 500,
"results": [...
}
Having brought that up, lets digest your lines, in TMDbApi.kt, you have indicated that your expected response is a List<MoviesResponse> which conflicts the response you receive as it is a JSON of type MoviesResponse,
Fix:
...): Call<List<MoviesResponse>>
}
to:
): Call<MoviesResponse>
}
The rest are small fixes to align your response handling.
Head over to AllMoviesActivity.kt and change the following:
class AllMoviesActivity : AppCompatActivity(), Callback<List<MoviesResponse>> {
to
class MainActivity : AppCompatActivity(), Callback<MoviesResponse>
Then on the callback functions, change signatures like so:
override fun onResponse(call: retrofit2.Call<List<MoviesResponse>>, response: Response<List<MoviesResponse>>) {
val moviesResponse = response.body() ?: listOf() ...
to:
override fun onResponse(call: Call<MoviesResponse>, response:Response<MoviesResponse>
) {
val moviesResponse = response.body()//type will be inferred ...
Then finally,
override fun onFailure(call: retrofit2.Call<List<MoviesResponse>>, t: Throwable) {
to:
override fun onFailure(call: Call<MoviesResponse>, t: Throwable) {
That's the basic to get the response and keep the Failure toast at bay.
Parting shot
Make the logs your friend, they can reveal the messy & smallest misses