feat: 홈 화면 무한 스크롤 기능 구현 (#109)

* build: pagination라이브러리 추가

* feat: 홈 화면 무한 스크롤 기능 구현

android/app/build.gradle.kts

@@ -135,6 +135,10 @@ dependencies {
     androidTestImplementation("androidx.test.ext:junit:1.1.5")
     androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
     androidTestImplementation("androidx.test:runner:1.4.0")
+
     // Espresso RecyclerView Actions
     androidTestImplementation("androidx.test.espresso:espresso-contrib:3.3.0")
+
+    // Pagination
+    implementation("androidx.paging:paging-runtime-ktx:3.3.0")
 }

android/app/src/main/java/com/zzang/chongdae/data/repository/remote/OfferingsRepositoryImpl.kt

@@ -11,9 +11,9 @@ class OfferingsRepositoryImpl(
     override suspend fun fetchOfferings(
         lastOfferingId: Long,
         pageSize: Int,
-    ): Result<List<Offering>> {
+    ): List<Offering> {
         return offeringsDataSource.fetchOfferings(lastOfferingId, pageSize).mapCatching {
             it.offerings.map { it.toDomain() }
-        }
+        }.getOrThrow()
     }
 }

android/app/src/main/java/com/zzang/chongdae/domain/paging/OfferingPagingSource.kt

@@ -0,0 +1,33 @@
+package com.zzang.chongdae.domain.paging
+
+import androidx.paging.PagingSource
+import androidx.paging.PagingState
+import com.zzang.chongdae.domain.model.Offering
+
+class OfferingPagingSource(
+    private val fetchOfferings: suspend (lastOfferingId: Long, pageSize: Int) -> List<Offering>,
+) : PagingSource<Long, Offering>() {
+    override suspend fun load(params: LoadParams<Long>): LoadResult<Long, Offering> {
+        val lastOfferingId = params.key ?: INIT_LAST_OFFERING_ID
+        return runCatching {
+            val offerings = fetchOfferings(lastOfferingId, params.loadSize)
+            LoadResult.Page(
+                data = offerings,
+                prevKey = if (lastOfferingId == INIT_LAST_OFFERING_ID) null else lastOfferingId - params.loadSize,
+                nextKey = if (offerings.isEmpty()) null else lastOfferingId + params.loadSize,
+            )
+        }.onFailure { throwable ->
+            LoadResult.Error<Long, Offering>(throwable)
+        }.getOrThrow()
+    }
+
+    override fun getRefreshKey(state: PagingState<Long, Offering>): Long? {
+        return state.anchorPosition?.let { anchorPosition ->
+            state.closestPageToPosition(anchorPosition)?.prevKey
+        }
+    }
+
+    companion object {
+        private const val INIT_LAST_OFFERING_ID = 0L
+    }
+}

android/app/src/main/java/com/zzang/chongdae/domain/repository/OfferingsRepository.kt

@@ -6,5 +6,5 @@ interface OfferingsRepository {
     suspend fun fetchOfferings(
         lastOfferingId: Long,
         pageSize: Int,
-    ): Result<List<Offering>>
+    ): List<Offering>
 }

android/app/src/main/java/com/zzang/chongdae/presentation/view/home/HomeFragment.kt

@@ -61,15 +61,10 @@ class HomeFragment : Fragment(), OnArticleClickListener {
 
     private fun setUpOfferingsObserve() {
         viewModel.offerings.observe(viewLifecycleOwner) {
-            offeringAdapter.submitList(it)
+            offeringAdapter.submitData(viewLifecycleOwner.lifecycle, it)
         }
     }
 
-    override fun onStart() {
-        super.onStart()
-        viewModel.updateArticles()
-    }
-
     override fun onClick(offeringId: Long) {
         OfferingDetailActivity.startActivity(activity as Context, offeringId)
     }

android/app/src/main/java/com/zzang/chongdae/presentation/view/home/OfferingViewModel.kt

@@ -1,26 +1,28 @@
 package com.zzang.chongdae.presentation.view.home
 
 import androidx.lifecycle.LiveData
-import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
+import androidx.paging.Pager
+import androidx.paging.PagingConfig
+import androidx.paging.PagingData
+import androidx.paging.cachedIn
+import androidx.paging.liveData
 import com.zzang.chongdae.domain.model.Offering
+import com.zzang.chongdae.domain.paging.OfferingPagingSource
 import com.zzang.chongdae.domain.repository.OfferingsRepository
-import kotlinx.coroutines.launch
 
 class OfferingViewModel(
     private val offeringsRepository: OfferingsRepository,
 ) : ViewModel() {
-    private val _offerings: MutableLiveData<List<Offering>> = MutableLiveData()
-    val offerings: LiveData<List<Offering>> get() = _offerings
+    val offerings: LiveData<PagingData<Offering>> =
+        Pager(
+            config = PagingConfig(pageSize = PAGE_SIZE, enablePlaceholders = false),
+            pagingSourceFactory = { OfferingPagingSource(fetchOfferings = offeringsRepository::fetchOfferings) },
+        ).liveData
+            .cachedIn(viewModelScope)
 
-    // 무한 스크롤 적용 시 수정 예정
-    fun updateArticles() {
-        viewModelScope.launch {
-            offeringsRepository.fetchOfferings(0L, 100).onSuccess {
-                _offerings.value = it
-            }.onFailure {
-            }
-        }
+    companion object {
+        private const val PAGE_SIZE = 10
     }
 }

android/app/src/main/java/com/zzang/chongdae/presentation/view/home/adapter/OfferingAdapter.kt

@@ -2,15 +2,15 @@ package com.zzang.chongdae.presentation.view.home.adapter
 
 import android.view.LayoutInflater
 import android.view.ViewGroup
+import androidx.paging.PagingDataAdapter
 import androidx.recyclerview.widget.DiffUtil
-import androidx.recyclerview.widget.ListAdapter
 import com.zzang.chongdae.databinding.ItemOfferingBinding
 import com.zzang.chongdae.domain.model.Offering
 import com.zzang.chongdae.presentation.view.home.OnArticleClickListener
 
 class OfferingAdapter(
     private val onArticleClickListener: OnArticleClickListener,
-) : ListAdapter<Offering, OfferingViewHolder>(productComparator) {
+) : PagingDataAdapter<Offering, OfferingViewHolder>(productComparator) {
     override fun onCreateViewHolder(
         parent: ViewGroup,
         viewType: Int,
@@ -24,7 +24,7 @@ class OfferingAdapter(
         holder: OfferingViewHolder,
         position: Int,
     ) {
-        holder.bind(getItem(position), onArticleClickListener)
+        getItem(position)?.let { holder.bind(it, onArticleClickListener) }
     }
 
     companion object {