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journal: add initial refresh support and paging
Due to the potentially large number of journal entries, the Paging library is introduced to avoid holding too many entries in memory. The `JournalPagingSource` is responsible for grabbing the correct pages of data from Room. It also observes the refresh status and invalidates itself after a refresh event. The synchronization is done on the first load of the journal screen and then only on demand.
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app/src/main/java/com/teobaranga/monica/data/sync/Synchronizer.kt
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,10 @@ | ||
| package com.teobaranga.monica.data.sync | ||
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| interface Synchronizer { | ||
| suspend fun sync() | ||
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| enum class State { | ||
| IDLE, | ||
| REFRESHING, | ||
| } | ||
| } |
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app/src/main/java/com/teobaranga/monica/journal/data/JournalPagingSource.kt
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,86 @@ | ||
| package com.teobaranga.monica.journal.data | ||
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| import androidx.paging.PagingSource | ||
| import androidx.paging.PagingState | ||
| import com.teobaranga.monica.data.sync.Synchronizer | ||
| import com.teobaranga.monica.database.OrderBy | ||
| import com.teobaranga.monica.journal.database.JournalDao | ||
| import com.teobaranga.monica.journal.database.toExternalModel | ||
| import com.teobaranga.monica.journal.model.JournalEntry | ||
| import com.teobaranga.monica.util.coroutines.Dispatcher | ||
| import dagger.assisted.Assisted | ||
| import dagger.assisted.AssistedFactory | ||
| import dagger.assisted.AssistedInject | ||
| import kotlinx.coroutines.CoroutineScope | ||
| import kotlinx.coroutines.SupervisorJob | ||
| import kotlinx.coroutines.cancel | ||
| import kotlinx.coroutines.flow.first | ||
| import kotlinx.coroutines.flow.map | ||
| import kotlinx.coroutines.flow.reduce | ||
| import kotlinx.coroutines.launch | ||
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| private const val STARTING_KEY = 0 | ||
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| internal class JournalPagingSource @AssistedInject constructor( | ||
| dispatcher: Dispatcher, | ||
| private val journalDao: JournalDao, | ||
| private val journalSynchronizer: JournalSynchronizer, | ||
| @Assisted | ||
| private val orderBy: JournalRepository.OrderBy, | ||
| ) : PagingSource<Int, JournalEntry>() { | ||
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| private val scope = CoroutineScope(SupervisorJob() + dispatcher.io) | ||
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| init { | ||
| scope.launch { | ||
| journalSynchronizer.syncState | ||
| .reduce { prev, new -> | ||
| if (prev == Synchronizer.State.REFRESHING && new == Synchronizer.State.IDLE) { | ||
| scope.cancel() | ||
| invalidate() | ||
| } | ||
| new | ||
| } | ||
| } | ||
| } | ||
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| override suspend fun load(params: LoadParams<Int>): LoadResult<Int, JournalEntry> { | ||
| // Start paging with the STARTING_KEY if this is the first load | ||
| val start = params.key ?: STARTING_KEY | ||
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| val entries = getEntries(start, params) | ||
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| return LoadResult.Page( | ||
| data = entries, | ||
| // Make sure we don't try to load items behind the STARTING_KEY | ||
| prevKey = if (start == 0) null else start - 1, | ||
| nextKey = if (entries.isEmpty()) null else start + 1, | ||
| ) | ||
| } | ||
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| override fun getRefreshKey(state: PagingState<Int, JournalEntry>): Int? { | ||
| return state.anchorPosition?.let { anchorPosition -> | ||
| val anchorPage = state.closestPageToPosition(anchorPosition) | ||
| anchorPage?.prevKey?.plus(1) ?: anchorPage?.nextKey?.minus(1) | ||
| } | ||
| } | ||
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| private suspend fun getEntries(start: Int, params: LoadParams<Int>): List<JournalEntry> { | ||
| return journalDao.getJournalEntries( | ||
| orderBy = with(orderBy) { OrderBy(columnName, isAscending) }, | ||
| limit = params.loadSize, | ||
| offset = start * params.loadSize, | ||
| ).map { journalEntryEntities -> | ||
| journalEntryEntities.map { | ||
| it.toExternalModel() | ||
| } | ||
| }.first() | ||
| } | ||
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| @AssistedFactory | ||
| internal interface Factory { | ||
| fun create(orderBy: JournalRepository.OrderBy): JournalPagingSource | ||
| } | ||
| } |
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