[TIL]221116 - Kotlin Volley ViewModel

//MainActivity.kt

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private lateinit var model: SongViewModel
    private var songs: Array<String>? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        model = ViewModelProvider(this)[SongViewModel::class.java] // this: context
        /**
         * [songViewModel] 해시맵으로 생각함
         * get...Model 대신 사용
         */


        model.requestSong()

        model.songs.observe(this, Observer<ArrayList<String>> {
//            Toast.makeText(this, model.songs.value.toString(), Toast.LENGTH_LONG).show()
            songs = model.songs.value?.toTypedArray()
            /**
             * 단지 asynchronous(비동기성의)하게 호출하기 때문에 (observer 사용하지 않은 경우)
             * request가 콜백함수를 통해 값을 넣고 다시 반환해줌
             * 초기화 값이 빈배열이기 때문에 이 부분(songs = ...)을 그냥 지나치게 되면서 그대로 출력됨
             */

            binding.listSongs.adapter = ArrayAdapter<String> (this, android.R.layout.simple_list_item_1, songs as Array<out String>)
        })

    }
}

//SongViewModel.kt

class SongViewModel(application: Application) : AndroidViewModel(application) {
    companion object {
        /**
         * Request Tag 생성
         */
        const val  QUEUE_TAG = "SongVolleyRequest"
    }
    private val list = ArrayList<String>()
    val songs = MutableLiveData<ArrayList<String>>()

    private var queue: RequestQueue
    init {
        songs.value = list
        queue = Volley.newRequestQueue(getApplication())
    }

    fun requestSong() {
        val url = "https://expreesongdb-hoaos.run.goorm.io"

        val request = JsonArrayRequest(
            Request.Method.GET,
            url,
            null,
            {
                list.clear() // 리스트 비워주기
                parseJson(it)
                songs.value = list //songs의 값에 넣어줘야 observer가 동작함
                Toast.makeText(getApplication(), list.toString(), Toast.LENGTH_LONG).show()
            },
            {
                Toast.makeText(getApplication(), it.toString(), Toast.LENGTH_LONG).show()
            }
        )

        request.tag = QUEUE_TAG
        queue.add(request)
    }
    //volley -> pascal case

    private fun parseJson(items: JSONArray) {
        for (i in 0 until items.length()) {
            val item: JSONObject = items[i] as JSONObject
            val id = item.getInt("id")
            val title = item.getString("title")
            val singer = item.getString("singer")

            list.add("$title ($singer)")
        }
    }

    override fun onCleared() {
        super.onCleared()
        queue.cancelAll(QUEUE_TAG)
    }

}

val songs = MutableLiveData<ArrayList<String>>()

실습 결과 화면