Use UI state classes in playlist

Author: Isira-Seneviratne

app/src/main/java/org/schabi/newpipe/ui/screens/PlaylistScreen.kt

@@ -5,11 +5,11 @@ import androidx.compose.foundation.lazy.grid.GridItemSpan
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.tooling.preview.Preview
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
 import androidx.paging.PagingData
 import androidx.paging.compose.collectAsLazyPagingItems
@@ -23,48 +23,67 @@ import org.schabi.newpipe.ui.components.items.ItemList
 import org.schabi.newpipe.ui.components.items.stream.StreamInfoItem
 import org.schabi.newpipe.ui.components.playlist.PlaylistHeader
 import org.schabi.newpipe.ui.components.playlist.PlaylistInfo
+import org.schabi.newpipe.ui.emptystate.EmptyStateComposable
+import org.schabi.newpipe.ui.emptystate.EmptyStateSpec
 import org.schabi.newpipe.ui.theme.AppTheme
 import org.schabi.newpipe.viewmodels.PlaylistViewModel
+import org.schabi.newpipe.viewmodels.util.Resource
 
 @Composable
 fun PlaylistScreen(playlistViewModel: PlaylistViewModel = viewModel()) {
     Surface(color = MaterialTheme.colorScheme.background) {
-        val playlistInfo by playlistViewModel.playlistInfo.collectAsState()
-        PlaylistScreen(playlistInfo, playlistViewModel.streamItems)
+        val uiState by playlistViewModel.uiState.collectAsStateWithLifecycle()
+        PlaylistScreen(uiState, playlistViewModel.streamItems)
     }
 }
 
 @Composable
 private fun PlaylistScreen(
-    playlistInfo: PlaylistInfo?,
+    uiState: Resource<PlaylistInfo>,
     streamFlow: Flow<PagingData<StreamInfoItem>>
 ) {
-    playlistInfo?.let {
-        val streams = streamFlow.collectAsLazyPagingItems()
+    when (uiState) {
+        is Resource.Success -> {
+            val info = uiState.data
+            val streams = streamFlow.collectAsLazyPagingItems()
 
-        // Paging's load states only indicate when loading is currently happening, not if it can/will
-        // happen. As such, the duration initially displayed will be the incomplete duration if more
-        // items can be loaded.
-        val totalDuration by remember {
-            derivedStateOf {
-                streams.itemSnapshotList.sumOf { it!!.duration }
+            // Paging's load states only indicate when loading is currently happening, not if it can/will
+            // happen. As such, the duration initially displayed will be the incomplete duration if more
+            // items can be loaded.
+            val totalDuration by remember {
+                derivedStateOf {
+                    streams.itemSnapshotList.sumOf { it!!.duration }
+                }
             }
-        }
 
-        ItemList(
-            items = streams,
-            gridHeader = {
-                item(span = { GridItemSpan(maxLineSpan) }) {
-                    PlaylistHeader(it, totalDuration)
-                }
-            },
-            listHeader = {
-                item {
-                    PlaylistHeader(it, totalDuration)
+            ItemList(
+                items = streams,
+                gridHeader = {
+                    item(span = { GridItemSpan(maxLineSpan) }) {
+                        PlaylistHeader(info, totalDuration)
+                    }
+                },
+                listHeader = {
+                    item {
+                        PlaylistHeader(info, totalDuration)
+                    }
                 }
-            }
-        )
-    } ?: LoadingIndicator()
+            )
+        }
+
+        is Resource.Loading -> {
+            LoadingIndicator()
+        }
+
+        is Resource.Error -> {
+            // TODO use error panel instead
+            EmptyStateComposable(
+                EmptyStateSpec.DisabledComments.copy(
+                    descriptionText = { "Could not load streams" }
+                )
+            )
+        }
+    }
 }
 
 @Preview(name = "Light mode", uiMode = Configuration.UI_MODE_NIGHT_NO)
@@ -81,7 +100,7 @@ private fun PlaylistPreview() {
 
     AppTheme {
         Surface(color = MaterialTheme.colorScheme.background) {
-            PlaylistScreen(playlistInfo, streamFlow)
+            PlaylistScreen(Resource.Success(playlistInfo), streamFlow)
         }
     }
 }

app/src/main/java/org/schabi/newpipe/viewmodels/PlaylistViewModel.kt

@@ -10,7 +10,7 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.combine
-import kotlinx.coroutines.flow.filterNotNull
+import kotlinx.coroutines.flow.filterIsInstance
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.stateIn
@@ -21,30 +21,37 @@ import org.schabi.newpipe.ui.components.playlist.PlaylistInfo
 import org.schabi.newpipe.util.KEY_SERVICE_ID
 import org.schabi.newpipe.util.KEY_URL
 import org.schabi.newpipe.util.NO_SERVICE_ID
+import org.schabi.newpipe.viewmodels.util.Resource
 import org.schabi.newpipe.extractor.playlist.PlaylistInfo as ExtractorPlaylistInfo
 
 class PlaylistViewModel(savedStateHandle: SavedStateHandle) : ViewModel() {
     private val serviceIdState = savedStateHandle.getStateFlow(KEY_SERVICE_ID, NO_SERVICE_ID)
     private val urlState = savedStateHandle.getStateFlow(KEY_URL, "")
 
-    val playlistInfo = serviceIdState.combine(urlState) { id, url ->
-        val info = ExtractorPlaylistInfo.getInfo(NewPipe.getService(id), url)
-        val description = info.description ?: Description.EMPTY_DESCRIPTION
-        PlaylistInfo(
-            info.id, info.serviceId, info.url, info.name, description, info.relatedItems,
-            info.streamCount, info.uploaderUrl, info.uploaderName, info.uploaderAvatars,
-            info.nextPage
-        )
+    val uiState = serviceIdState.combine(urlState) { id, url ->
+        try {
+            val extractorInfo = ExtractorPlaylistInfo.getInfo(NewPipe.getService(id), url)
+            val description = extractorInfo.description ?: Description.EMPTY_DESCRIPTION
+            val info = PlaylistInfo(
+                extractorInfo.id, extractorInfo.serviceId, extractorInfo.url, extractorInfo.name,
+                description, extractorInfo.relatedItems, extractorInfo.streamCount,
+                extractorInfo.uploaderUrl, extractorInfo.uploaderName, extractorInfo.uploaderAvatars,
+                extractorInfo.nextPage
+            )
+            Resource.Success(info)
+        } catch (e: Exception) {
+            Resource.Error(e)
+        }
     }
         .flowOn(Dispatchers.IO)
-        .stateIn(viewModelScope, SharingStarted.Eagerly, null)
+        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(), Resource.Loading)
 
     @OptIn(ExperimentalCoroutinesApi::class)
-    val streamItems = playlistInfo
-        .filterNotNull()
+    val streamItems = uiState
+        .filterIsInstance<Resource.Success<PlaylistInfo>>()
         .flatMapLatest {
             Pager(PagingConfig(pageSize = 20, enablePlaceholders = false)) {
-                PlaylistItemsSource(it)
+                PlaylistItemsSource(it.data)
             }.flow
         }
         .cachedIn(viewModelScope)