Implemented the actual sorting.

app/src/main/java/de/ph1b/audiobook/features/bookCategory/BookCategoryController.kt

@@ -37,17 +37,18 @@ class BookCategoryController(bundle: Bundle) : BaseController(bundle), EditBookB
   @Inject
   lateinit var galleryPicker: GalleryPicker
 
-  init {
-    appComponent.inject(this)
-  }
-
   constructor(category: BookOverviewCategory) : this(Bundle().apply {
     putSerializable(NI_CATEGORY, category)
   })
 
   private val category = bundle.getSerializable(NI_CATEGORY) as BookOverviewCategory
   private var adapter by clearAfterDestroyView<BookCategoryAdapter>()
 
+  init {
+    appComponent.inject(this)
+    viewModel.category = category
+  }
+
   override val layoutRes = R.layout.book_category
 
   override fun onViewCreated() {
@@ -84,7 +85,7 @@ class BookCategoryController(bundle: Bundle) : BaseController(bundle), EditBookB
     recyclerView.addItemDecoration(BookCategoryItemDecoration(activity, layoutManager))
     (recyclerView.itemAnimator as DefaultItemAnimator).supportsChangeAnimations = false
 
-    viewModel.get(category)
+    viewModel.get()
       .subscribe {
         layoutManager.spanCount = it.gridColumnCount
         adapter.submitList(it.models)

app/src/main/java/de/ph1b/audiobook/features/bookCategory/BookCategoryViewModel.kt

@@ -21,16 +21,26 @@ class BookCategoryViewModel
   private val currentBookIdPref: Pref<UUID>,
   @Named(PrefKeys.GRID_MODE)
   private val gridModePref: Pref<GridMode>,
-  private val gridCount: GridCount
+  private val gridCount: GridCount,
+  private val comparatorPrefForCategory: @JvmSuppressWildcards Map<BookOverviewCategory, Pref<BookComparator>>
 ) {
 
-  fun get(category: BookOverviewCategory): Observable<BookCategoryState> {
-    return Observables.combineLatest(gridModePref.stream, repo.booksStream()) { gridMode, books ->
+  lateinit var category: BookOverviewCategory
+
+  private fun comparatorPref(): Pref<BookComparator> = comparatorPrefForCategory[category]!!
+
+  fun get(): Observable<BookCategoryState> {
+    val comparatorStream = comparatorPref().stream
+    return Observables.combineLatest(
+      gridModePref.stream,
+      repo.booksStream(),
+      comparatorStream
+    ) { gridMode, books, comparator ->
       val gridColumnCount = gridCount.gridColumnCount(gridMode)
       val currentBookId = currentBookIdPref.value
       val models = books.asSequence()
         .filter(category.filter)
-        .sortedWith(BookComparator.BY_NAME)
+        .sortedWith(comparator)
         .map { book ->
           BookOverviewModel(
             book = book,
@@ -44,12 +54,12 @@ class BookCategoryViewModel
   }
 
   fun sort(comparator: BookComparator) {
+    comparatorPref().value = comparator
   }
 
   fun bookSorting(): BookComparator {
-    return BookComparator.BY_NAME
+    return comparatorPref().value
   }
-
 }
 
 data class BookCategoryState(

app/src/main/java/de/ph1b/audiobook/injection/AppComponent.kt

@@ -41,7 +41,8 @@ import javax.inject.Singleton
     AndroidModule::class,
     PrefsModule::class,
     PersistenceModule::class,
-    PlaybackModule::class
+    PlaybackModule::class,
+    SortingModule::class
   ]
 )
 interface AppComponent : DataComponent {

app/src/main/java/de/ph1b/audiobook/injection/SortingModule.kt

@@ -0,0 +1,49 @@
+package de.ph1b.audiobook.injection
+
+import com.f2prateek.rx.preferences2.RxSharedPreferences
+import dagger.MapKey
+import dagger.Module
+import dagger.Provides
+import dagger.multibindings.IntoMap
+import de.ph1b.audiobook.features.bookOverview.list.BookComparator
+import de.ph1b.audiobook.features.bookOverview.list.header.BookOverviewCategory
+import de.ph1b.audiobook.persistence.pref.PersistentPref
+import de.ph1b.audiobook.persistence.pref.Pref
+import javax.inject.Singleton
+
+@MapKey
+annotation class BookOverviewCategoryKey(val value: BookOverviewCategory)
+
+@Module
+object SortingModule {
+
+  @JvmStatic
+  @Provides
+  @Singleton
+  @IntoMap
+  @BookOverviewCategoryKey(BookOverviewCategory.CURRENT)
+  fun currentComparatorPref(prefs: RxSharedPreferences): Pref<BookComparator> {
+    val pref = prefs.getEnum(BookOverviewCategory.CURRENT.name, BookComparator.BY_NAME, BookComparator::class.java)
+    return PersistentPref(pref)
+  }
+
+  @JvmStatic
+  @Provides
+  @Singleton
+  @IntoMap
+  @BookOverviewCategoryKey(BookOverviewCategory.NOT_STARTED)
+  fun notStartedComparatorPref(prefs: RxSharedPreferences): Pref<BookComparator> {
+    val pref = prefs.getEnum(BookOverviewCategory.NOT_STARTED.name, BookComparator.BY_NAME, BookComparator::class.java)
+    return PersistentPref(pref)
+  }
+
+  @JvmStatic
+  @Provides
+  @Singleton
+  @IntoMap
+  @BookOverviewCategoryKey(BookOverviewCategory.FINISHED)
+  fun finishedComparatorPref(prefs: RxSharedPreferences): Pref<BookComparator> {
+    val pref = prefs.getEnum(BookOverviewCategory.FINISHED.name, BookComparator.BY_NAME, BookComparator::class.java)
+    return PersistentPref(pref)
+  }
+}

app/src/main/java/de/ph1b/audiobook/misc/Observables.kt

@@ -3,6 +3,7 @@ package de.ph1b.audiobook.misc
 import io.reactivex.Observable
 import io.reactivex.ObservableSource
 import io.reactivex.functions.BiFunction
+import io.reactivex.functions.Function3
 import io.reactivex.functions.Function5
 
 object Observables {
@@ -15,6 +16,15 @@ object Observables {
     return Observable.combineLatest(source1, source2, BiFunction { t1, t2 -> combiner(t1, t2) })
   }
 
+  inline fun <T1 : Any, T2 : Any, T3 : Any, R : Any> combineLatest(
+    source1: ObservableSource<T1>,
+    source2: ObservableSource<T2>,
+    source3: ObservableSource<T3>,
+    crossinline combiner: (T1, T2, T3) -> R
+  ): Observable<R> {
+    return Observable.combineLatest(source1, source2, source3, Function3 { t1, t2, t3 -> combiner(t1, t2, t3) })
+  }
+
   inline fun <T1 : Any, T2 : Any, T3 : Any, T4 : Any, T5 : Any, R : Any> combineLatest(
     source1: ObservableSource<T1>,
     source2: ObservableSource<T2>,