Collapsible sort group headers

app/src/androidTest/java/com/todoroo/astrid/adapter/CaldavManualSortTaskAdapterTest.kt

@@ -41,7 +41,7 @@ class CaldavManualSortTaskAdapterTest : InjectingTestCase() {
     private val dataSource = object : TaskAdapterDataSource {
         override fun getItem(position: Int) = tasks[position]
 
-        override fun getItemCount() = tasks.size
+        override fun getTaskCount() = tasks.size
     }
 
     @Before

app/src/androidTest/java/com/todoroo/astrid/adapter/CaldavTaskAdapterTest.kt

@@ -36,7 +36,7 @@ class CaldavTaskAdapterTest : InjectingTestCase() {
         adapter.setDataSource(object : TaskAdapterDataSource {
             override fun getItem(position: Int) = tasks[position]
 
-            override fun getItemCount() = tasks.size
+            override fun getTaskCount() = tasks.size
         })
     }
 

app/src/androidTest/java/com/todoroo/astrid/adapter/GoogleTaskManualSortAdapterTest.kt

@@ -40,7 +40,7 @@ class GoogleTaskManualSortAdapterTest : InjectingTestCase() {
     private val dataSource = object : TaskAdapterDataSource {
         override fun getItem(position: Int) = tasks[position]
 
-        override fun getItemCount() = tasks.size
+        override fun getTaskCount() = tasks.size
     }
 
     @Test

app/src/main/java/com/todoroo/astrid/activity/MainActivity.kt

@@ -404,6 +404,7 @@ class MainActivity : InjectingAppCompatActivity(), TaskListFragmentCallbackHandl
     }
 
     override fun sortChanged(reload: Boolean) {
+        taskListFragment?.clearCollapsed()
         localBroadcastManager.broadcastRefresh()
         if (reload) {
             openTaskListFragment(filter, true)

app/src/main/java/com/todoroo/astrid/activity/TaskListFragment.kt

@@ -167,7 +167,7 @@ class TaskListFragment : InjectingFragment(), OnRefreshListener, Toolbar.OnMenuI
         if (savedInstanceState != null) {
             val longArray = savedInstanceState.getLongArray(EXTRA_SELECTED_TASK_IDS)
             if (longArray?.isNotEmpty() == true) {
-                taskAdapter.setSelected(*longArray)
+                taskAdapter.setSelected(longArray.toList())
                 startActionMode()
             }
         }
@@ -185,6 +185,7 @@ class TaskListFragment : InjectingFragment(), OnRefreshListener, Toolbar.OnMenuI
         val selectedTaskIds: List<Long> = taskAdapter.getSelected()
         outState.putLongArray(EXTRA_SELECTED_TASK_IDS, selectedTaskIds.toLongArray())
         outState.putString(EXTRA_SEARCH, searchQuery)
+        outState.putLongArray(EXTRA_COLLAPSED, taskAdapter.getCollapsed().toLongArray())
     }
 
     override fun onCreateView(
@@ -197,6 +198,7 @@ class TaskListFragment : InjectingFragment(), OnRefreshListener, Toolbar.OnMenuI
 
         // set up list adapters
         taskAdapter = taskAdapterProvider.createTaskAdapter(filter)
+        taskAdapter.setCollapsed(savedInstanceState?.getLongArray(EXTRA_COLLAPSED))
         taskListViewModel = ViewModelProvider(requireActivity()).get(TaskListViewModel::class.java)
         if (savedInstanceState != null) {
             searchQuery = savedInstanceState.getString(EXTRA_SEARCH)
@@ -231,13 +233,13 @@ class TaskListFragment : InjectingFragment(), OnRefreshListener, Toolbar.OnMenuI
             if (recyclerAdapter !is PagedListRecyclerAdapter) {
                 setAdapter(
                         PagedListRecyclerAdapter(
-                                taskAdapter, recyclerView, viewHolderFactory, this, tasks, taskDao))
+                                taskAdapter, recyclerView, viewHolderFactory, this, tasks, taskDao, preferences))
                 return
             }
         } else if (recyclerAdapter !is DragAndDropRecyclerAdapter) {
             setAdapter(
                     DragAndDropRecyclerAdapter(
-                            taskAdapter, recyclerView, viewHolderFactory, this, tasks as MutableList, taskDao))
+                            taskAdapter, recyclerView, viewHolderFactory, this, tasks as MutableList, taskDao, preferences))
             return
         }
         recyclerAdapter!!.submitList(tasks)
@@ -740,6 +742,8 @@ class TaskListFragment : InjectingFragment(), OnRefreshListener, Toolbar.OnMenuI
         makeSnackbar(R.string.copy_multiple_tasks_confirmation, duplicates.size.toString()).show()
     }
 
+    fun clearCollapsed() = taskAdapter.clearCollapsed()
+
     companion object {
         const val TAGS_METADATA_JOIN = "for_tags" // $NON-NLS-1$
         const val GTASK_METADATA_JOIN = "googletask" // $NON-NLS-1$
@@ -748,6 +752,7 @@ class TaskListFragment : InjectingFragment(), OnRefreshListener, Toolbar.OnMenuI
         const val ACTION_DELETED = "action_deleted"
         private const val EXTRA_SELECTED_TASK_IDS = "extra_selected_task_ids"
         private const val EXTRA_SEARCH = "extra_search"
+        private const val EXTRA_COLLAPSED = "extra_collapsed"
         private const val VOICE_RECOGNITION_REQUEST_CODE = 1234
         private const val EXTRA_FILTER = "extra_filter"
         private const val FRAG_TAG_REMOTE_LIST_PICKER = "frag_tag_remote_list_picker"

app/src/main/java/com/todoroo/astrid/adapter/CaldavTaskAdapter.kt

@@ -12,6 +12,9 @@ open class CaldavTaskAdapter internal constructor(private val taskDao: TaskDao,
 
     override fun minIndent(nextPosition: Int, task: TaskContainer): Int {
         (nextPosition until count).forEach {
+            if (isHeader(it)) {
+                return 0
+            }
             if (!taskIsChild(task, it)) {
                 return getTask(it).indent
             }
@@ -79,6 +82,9 @@ open class CaldavTaskAdapter internal constructor(private val taskDao: TaskDao,
 
     private fun taskIsChild(source: TaskContainer, destinationIndex: Int): Boolean {
         (destinationIndex downTo 0).forEach {
+            if (isHeader(it)) {
+                return false
+            }
             when (getTask(it).parent) {
                 0L -> return false
                 source.parent -> return false

app/src/main/java/com/todoroo/astrid/adapter/TaskAdapter.kt

@@ -11,10 +11,11 @@ import java.util.*
 
 open class TaskAdapter {
     private val selected = HashSet<Long>()
+    private val collapsed = HashSet<Long>()
     private lateinit var dataSource: TaskAdapterDataSource
 
     val count: Int
-        get() = dataSource.getItemCount()
+        get() = dataSource.getTaskCount()
 
     fun setDataSource(dataSource: TaskAdapterDataSource) {
         this.dataSource = dataSource
@@ -25,15 +26,22 @@ open class TaskAdapter {
 
     fun getSelected(): ArrayList<Long> = ArrayList(selected)
 
-    fun setSelected(vararg ids: Long) = setSelected(ids.toList())
-
     fun setSelected(ids: Collection<Long>) {
-        selected.clear()
+        clearSelections()
         selected.addAll(ids)
     }
 
     fun clearSelections() = selected.clear()
 
+    fun getCollapsed(): ArrayList<Long> = ArrayList(collapsed)
+
+    fun setCollapsed(groups: LongArray?) {
+        clearCollapsed()
+        groups?.toList()?.let(collapsed::addAll)
+    }
+
+    fun clearCollapsed() = collapsed.clear()
+
     open fun getIndent(task: TaskContainer): Int = task.getIndent()
 
     open fun canMove(source: TaskContainer, from: Int, target: TaskContainer, to: Int): Boolean = false
@@ -53,12 +61,22 @@ open class TaskAdapter {
         }
     }
 
+    fun toggleCollapsed(group: Long) {
+        if (collapsed.contains(group)) {
+            collapsed.remove(group)
+        } else {
+            collapsed.add(group)
+        }
+    }
+
     open fun supportsParentingOrManualSort(): Boolean = false
 
     open fun supportsManualSorting(): Boolean = false
 
     open fun moved(from: Int, to: Int, indent: Int) {}
 
+    fun isHeader(position: Int): Boolean = dataSource.isHeader(position)
+
     fun getTask(position: Int): TaskContainer = dataSource.getItem(position)
 
     fun getItemUuid(position: Int): String = getTask(position).uuid

app/src/main/java/com/todoroo/astrid/adapter/TaskAdapterDataSource.kt

@@ -5,5 +5,7 @@ import org.tasks.data.TaskContainer
 interface TaskAdapterDataSource {
     fun getItem(position: Int): TaskContainer
 
-    fun getItemCount(): Int
+    fun getTaskCount(): Int
+
+    fun isHeader(position: Int): Boolean = false
 }

app/src/main/java/com/todoroo/astrid/core/SortHelper.java

@@ -11,6 +11,7 @@ import static org.tasks.db.QueryUtils.showHidden;
 import static org.tasks.db.QueryUtils.showRecentlyCompleted;
 
 import android.annotation.SuppressLint;
+import androidx.annotation.Nullable;
 import com.todoroo.andlib.sql.Functions;
 import com.todoroo.andlib.sql.Order;
 import com.todoroo.astrid.data.Task;
@@ -122,6 +123,21 @@ public class SortHelper {
     return order;
   }
 
+  public static @Nullable String getSortGroup(int sortType) {
+    switch (sortType) {
+      case SORT_DUE:
+        return "tasks.dueDate";
+      case SORT_IMPORTANCE:
+        return "tasks.importance";
+      case SORT_MODIFIED:
+        return "tasks.modified";
+      case SORT_CREATED:
+        return "tasks.created";
+      default:
+        return null;
+    }
+  }
+
   public static String orderSelectForSortTypeRecursive(int sortType) {
     String select;
     switch (sortType) {

app/src/main/java/org/tasks/data/TaskContainer.java

@@ -11,6 +11,7 @@ public class TaskContainer {
   @Embedded public Location location;
   public String tags;
   public int children;
+  public Long sortGroup;
   public long primarySort;
   public long secondarySort;
   public int indent;
@@ -52,6 +53,10 @@ public class TaskContainer {
     return task.hasDueDate();
   }
 
+  public boolean hasDueTime() {
+    return task.hasDueTime();
+  }
+
   public boolean isOverdue() {
     return task.isOverdue();
   }
@@ -107,14 +112,24 @@ public class TaskContainer {
         && Objects.equals(googletask, that.googletask)
         && Objects.equals(caldavTask, that.caldavTask)
         && Objects.equals(location, that.location)
-        && Objects.equals(tags, that.tags);
+        && Objects.equals(tags, that.tags)
+        && Objects.equals(sortGroup, that.sortGroup);
   }
 
   @Override
   public int hashCode() {
-    return Objects
+    return Objects.hash(
-        .hash(task, googletask, caldavTask, location, tags, children, primarySort,
+        task,
-            secondarySort, indent, targetIndent);
+        googletask,
+        caldavTask,
+        location,
+        tags,
+        children,
+        sortGroup,
+        primarySort,
+        secondarySort,
+        indent,
+        targetIndent);
   }
 
   @Override
@@ -133,6 +148,8 @@ public class TaskContainer {
         + '\''
         + ", children="
         + children
+        + ", sortGroup="
+        + sortGroup
         + ", primarySort="
         + primarySort
         + ", secondarySort="

app/src/main/java/org/tasks/data/TaskListQueryRecursive.kt

@@ -22,6 +22,7 @@ internal object TaskListQueryRecursive {
             TaskListQuery.FIELDS.plus(listOf(
                     field("(${Query.select(field("group_concat(distinct(tag_uid))")).from(Tag.TABLE).where(Task.ID.eq(Tag.TASK))} GROUP BY ${Tag.TASK})").`as`("tags"),
                     field("indent"),
+                    field("sort_group").`as`("sortGroup"),
                     field("children"),
                     field("primary_sort").`as`("primarySort"),
                     field("secondary_sort").`as`("secondarySort"))).toTypedArray()
@@ -94,10 +95,10 @@ internal object TaskListQueryRecursive {
         val sortSelect = SortHelper.orderSelectForSortTypeRecursive(sortMode)
         val withClause ="""
             CREATE TEMPORARY TABLE `recursive_tasks` AS
-            WITH RECURSIVE recursive_tasks (task, parent, collapsed, hidden, indent, title, sortField, primary_sort, secondary_sort) AS (
+            WITH RECURSIVE recursive_tasks (task, parent, collapsed, hidden, indent, title, sortField, primary_sort, secondary_sort, sort_group) AS (
-                SELECT tasks._id, 0 as parent, tasks.collapsed as collapsed, 0 as hidden, 0 AS sort_indent, UPPER(tasks.title) AS sort_title, $sortSelect, $sortField as primary_sort, NULL as secondarySort FROM tasks
+                SELECT tasks._id, 0 as parent, tasks.collapsed as collapsed, 0 as hidden, 0 AS sort_indent, UPPER(tasks.title) AS sort_title, $sortSelect, $sortField as primary_sort, NULL as secondarySort, ${SortHelper.getSortGroup(sortMode)} FROM tasks
                 $parentQuery
-                UNION ALL SELECT tasks._id, recursive_tasks.task as parent, tasks.collapsed as collapsed, CASE WHEN recursive_tasks.collapsed > 0 OR recursive_tasks.hidden > 0 THEN 1 ELSE 0 END as hidden, recursive_tasks.indent+1 AS sort_indent, UPPER(tasks.title) AS sort_title, $sortSelect, recursive_tasks.primary_sort as primary_sort, $sortField as secondary_sort FROM tasks
+                UNION ALL SELECT tasks._id, recursive_tasks.task as parent, tasks.collapsed as collapsed, CASE WHEN recursive_tasks.collapsed > 0 OR recursive_tasks.hidden > 0 THEN 1 ELSE 0 END as hidden, recursive_tasks.indent+1 AS sort_indent, UPPER(tasks.title) AS sort_title, $sortSelect, recursive_tasks.primary_sort as primary_sort, $sortField as secondary_sort, recursive_tasks.sort_group FROM tasks
                 $subtaskQuery
                 ORDER BY sort_indent DESC, ${SortHelper.orderForSortTypeRecursive(sortMode, reverseSort)}
             ) SELECT * FROM recursive_tasks

app/src/main/java/org/tasks/injection/ApplicationModule.kt

@@ -23,6 +23,10 @@ class ApplicationModule(@get:Provides @get:ForApplication val context: Context)
     val locale: Locale
         get() = Locale.getInstance(context)
 
+    @Provides
+    @ApplicationScope
+    fun getJavaLocale(locale: Locale): java.util.Locale = locale.locale
+
     @Provides
     @ApplicationScope
     fun getNotificationDao(db: Database): NotificationDao = db.notificationDao()

app/src/main/java/org/tasks/tasklist/AdapterSection.kt

@@ -0,0 +1,3 @@
+package org.tasks.tasklist
+
+data class AdapterSection(var firstPosition: Int, val value: Long, var sectionedPosition: Int = 0, var collapsed: Boolean = false)

app/src/main/java/org/tasks/tasklist/DiffCallback.kt

@@ -2,21 +2,32 @@ package org.tasks.tasklist
 
 import androidx.recyclerview.widget.DiffUtil
 import com.todoroo.astrid.adapter.TaskAdapter
-import org.tasks.data.TaskContainer
 
-internal class DiffCallback(private val old: List<TaskContainer>, private val new: List<TaskContainer>, @Deprecated("") private val adapter: TaskAdapter) : DiffUtil.Callback() {
+internal class DiffCallback(private val old: SectionedDataSource, private val new: SectionedDataSource, @Deprecated("") private val adapter: TaskAdapter) : DiffUtil.Callback() {
 
     override fun getOldListSize() = old.size
 
     override fun getNewListSize() = new.size
 
     override fun areItemsTheSame(oldPosition: Int, newPosition: Int): Boolean {
-        return old[oldPosition].id == new[newPosition].id
+        val wasHeader = old.isHeader(oldPosition)
+        val isHeader = new.isHeader(newPosition)
+        if (wasHeader != isHeader) {
+            return false
+        }
+        return if (isHeader) {
+            old.sortMode == new.sortMode && old.getHeaderValue(oldPosition) == new.getHeaderValue(newPosition)
+        } else {
+            old.getItem(oldPosition).id == new.getItem(newPosition).id
+        }
     }
 
     override fun areContentsTheSame(oldPosition: Int, newPosition: Int): Boolean {
-        val oldItem = old[oldPosition]
+        if (new.isHeader(newPosition)) {
-        val newItem = new[newPosition]
+            return old.getSection(oldPosition).collapsed == new.getSection(newPosition).collapsed
+        }
+        val oldItem = old.getItem(oldPosition)
+        val newItem = new.getItem(newPosition)
         return oldItem == newItem && oldItem.getIndent() == adapter.getIndent(newItem)
     }
 }

app/src/main/java/org/tasks/tasklist/DragAndDropRecyclerAdapter.kt

@@ -1,6 +1,7 @@
 package org.tasks.tasklist
 
 import android.graphics.Canvas
+import android.view.ViewGroup
 import androidx.core.util.Pair
 import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.ItemTouchHelper
@@ -11,11 +12,13 @@ import com.todoroo.astrid.activity.TaskListFragment
 import com.todoroo.astrid.adapter.TaskAdapter
 import com.todoroo.astrid.dao.TaskDao
 import com.todoroo.astrid.utility.Flags
+import io.reactivex.Single
 import io.reactivex.android.schedulers.AndroidSchedulers
 import io.reactivex.disposables.CompositeDisposable
 import io.reactivex.schedulers.Schedulers
 import io.reactivex.subjects.PublishSubject
 import org.tasks.data.TaskContainer
+import org.tasks.preferences.Preferences
 import java.util.*
 import kotlin.math.max
 import kotlin.math.min
@@ -25,27 +28,61 @@ class DragAndDropRecyclerAdapter(
         private val recyclerView: RecyclerView,
         viewHolderFactory: ViewHolderFactory,
         private val taskList: TaskListFragment,
-        private var list: MutableList<TaskContainer>,
+        tasks: MutableList<TaskContainer>,
-        taskDao: TaskDao) : TaskListRecyclerAdapter(adapter, viewHolderFactory, taskList, taskDao) {
+        taskDao: TaskDao,
-    private val publishSubject = PublishSubject.create<MutableList<TaskContainer>>()
+        preferences: Preferences) : TaskListRecyclerAdapter(adapter, viewHolderFactory, taskList, taskDao, preferences) {
+    private var list: SectionedDataSource
+    private val publishSubject = PublishSubject.create<SectionedDataSource>()
     private val disposables = CompositeDisposable()
-    private val updates: Queue<Pair<MutableList<TaskContainer>, DiffUtil.DiffResult>> = LinkedList()
+    private val updates: Queue<Pair<SectionedDataSource, DiffUtil.DiffResult>> = LinkedList()
     private var dragging = false
+    private val disableHeaders: Boolean
+
+    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
+        val viewType = getItemViewType(position)
+        if (viewType == 1) {
+            val headerSection = list.getSection(position)
+            (holder as HeaderViewHolder).bind(taskList.getFilter(), preferences.sortMode, headerSection)
+        } else {
+            super.onBindViewHolder(holder, position)
+        }
+    }
+
+    override fun getItemViewType(position: Int) = if (list.isHeader(position)) 1 else 0
+
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder = if (viewType == 1) {
+        viewHolderFactory.newHeaderViewHolder(parent, this::toggleGroup)
+    } else {
+        super.onCreateViewHolder(parent, viewType)
+    }
+
+    private fun toggleGroup(group: Long) {
+        adapter.toggleCollapsed(group)
+        taskList.loadTaskListContent()
+    }
+
     override fun dragAndDropEnabled() = adapter.supportsParentingOrManualSort()
 
-    override fun getItem(position: Int) = list[position]
+    override fun isHeader(position: Int): Boolean = list.isHeader(position)
+
+    override fun getItem(position: Int): TaskContainer = list.getItem(position)
 
-    override fun submitList(list: List<TaskContainer>) = publishSubject.onNext(list as MutableList<TaskContainer>)
+    override fun submitList(list: List<TaskContainer>) {
+        disposables.add(
+                Single.fromCallable { SectionedDataSource(list as MutableList, disableHeaders, preferences.sortMode, adapter.getCollapsed().toMutableSet()) }
+                        .subscribeOn(Schedulers.computation())
+                        .subscribe(publishSubject::onNext))
+    }
 
     private fun calculateDiff(
-            last: Pair<MutableList<TaskContainer>, DiffUtil.DiffResult>, next: MutableList<TaskContainer>): Pair<MutableList<TaskContainer>, DiffUtil.DiffResult> {
+            last: Pair<SectionedDataSource, DiffUtil.DiffResult>, next: SectionedDataSource): Pair<SectionedDataSource, DiffUtil.DiffResult> {
         AndroidUtilities.assertNotMainThread()
         val cb = DiffCallback(last.first!!, next, adapter)
         val result = DiffUtil.calculateDiff(cb, next.size < LONG_LIST_SIZE)
         return Pair.create(next, result)
     }
 
-    private fun applyDiff(update: Pair<MutableList<TaskContainer>, DiffUtil.DiffResult>) {
+    private fun applyDiff(update: Pair<SectionedDataSource, DiffUtil.DiffResult>) {
         AndroidUtilities.assertMainThread()
         updates.add(update)
         if (!dragging) {
@@ -67,9 +104,9 @@ class DragAndDropRecyclerAdapter(
 
     override fun onDetachedFromRecyclerView(recyclerView: RecyclerView) = disposables.dispose()
 
-    override fun getItemCount(): Int {
+    override fun getTaskCount() = list.taskCount
-        return list.size
+
-    }
+    override fun getItemCount() = list.size
 
     private inner class ItemTouchHelperCallback : ItemTouchHelper.Callback() {
         private var from = -1
@@ -85,10 +122,14 @@ class DragAndDropRecyclerAdapter(
             }
         }
 
-        override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder) = if (adapter.supportsParentingOrManualSort() && adapter.numSelected == 0) {
+        override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {
-            makeMovementFlags(ItemTouchHelper.UP or ItemTouchHelper.DOWN or ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT, 0)
+            return if (adapter.isHeader(viewHolder.adapterPosition)) {
-        } else {
+                makeMovementFlags(0, 0)
-            makeMovementFlags(0, 0)
+            } else if (adapter.supportsParentingOrManualSort() && adapter.numSelected == 0) {
+                makeMovementFlags(ItemTouchHelper.UP or ItemTouchHelper.DOWN or ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT, 0)
+            } else {
+                makeMovementFlags(0, 0)
+            }
         }
 
         override fun onMove(
@@ -99,7 +140,8 @@ class DragAndDropRecyclerAdapter(
             val fromPosition = src.adapterPosition
             val toPosition = target.adapterPosition
             val source = src as TaskViewHolder
-            if (!adapter.canMove(source.task, fromPosition, (target as TaskViewHolder).task, toPosition)) {
+            val isHeader = isHeader(toPosition)
+            if (!isHeader && !adapter.canMove(source.task, fromPosition, (target as TaskViewHolder).task, toPosition)) {
                 return false
             }
             if (from == -1) {
@@ -108,14 +150,19 @@ class DragAndDropRecyclerAdapter(
             }
             to = toPosition
             notifyItemMoved(fromPosition, toPosition)
+            if (isHeader) {
+                val offset = if (fromPosition < toPosition) -1 else 1
+                list.moveSection(toPosition, offset)
+            }
             updateIndents(source, from, to)
             return true
         }
 
         private fun updateIndents(source: TaskViewHolder?, from: Int, to: Int) {
             val task = source!!.task
-            source.minIndent = if (to == 0 || to == itemCount - 1) 0 else adapter.minIndent(if (from <= to) to + 1 else to, task)
+            val previousIsHeader = to > 0 && isHeader(to - 1)
-            source.maxIndent = if (to == 0) 0 else adapter.maxIndent(if (from >= to) to - 1 else to, task)
+            source.minIndent = if (to == 0 || to == itemCount - 1 || previousIsHeader) 0 else adapter.minIndent(if (from <= to) to + 1 else to, task)
+            source.maxIndent = if (to == 0 || previousIsHeader) 0 else adapter.maxIndent(if (from >= to) to - 1 else to, task)
         }
 
         override fun onChildDraw(
@@ -191,7 +238,14 @@ class DragAndDropRecyclerAdapter(
             throw UnsupportedOperationException()
         }
 
-        private fun moved(from: Int, to: Int, indent: Int) {
+        private fun moved(fromOrig: Int, to: Int, indent: Int) {
+            val from = if (fromOrig == to) {
+                to
+            } else if (fromOrig > to && isHeader(fromOrig)) {
+                from - 1
+            } else {
+                from
+            }
             adapter.moved(from, to, indent)
             val task: TaskContainer = list.removeAt(from)
             list.add(if (from < to) to - 1 else to, task)
@@ -204,16 +258,18 @@ class DragAndDropRecyclerAdapter(
     }
 
     init {
+        val filter = taskList.getFilter()
+        disableHeaders = !filter.supportsSorting() || preferences.isManualSort && filter.supportsManualSort()
         ItemTouchHelper(ItemTouchHelperCallback()).attachToRecyclerView(recyclerView)
-        val initial = Pair.create<MutableList<TaskContainer>, DiffUtil.DiffResult>(list, null)
+        list = SectionedDataSource(tasks, disableHeaders, preferences.sortMode, adapter.getCollapsed().toMutableSet())
-        disposables.add(
+        val initial = Pair.create<SectionedDataSource, DiffUtil.DiffResult>(list, null)
-                publishSubject
+        disposables.add(publishSubject
-                        .observeOn(Schedulers.computation())
+                .observeOn(Schedulers.computation())
-                        .scan(initial, { last: Pair<MutableList<TaskContainer>, DiffUtil.DiffResult>, next: List<TaskContainer> ->
+                .scan(initial, { last: Pair<SectionedDataSource, DiffUtil.DiffResult>, next: SectionedDataSource ->
-                            calculateDiff(last, next.toMutableList())
+                    calculateDiff(last, next)
-                        })
+                })
-                        .skip(1)
+                .skip(1)
-                        .observeOn(AndroidSchedulers.mainThread())
+                .observeOn(AndroidSchedulers.mainThread())
-                        .subscribe { update: Pair<MutableList<TaskContainer>, DiffUtil.DiffResult> -> applyDiff(update) })
+                .subscribe { update: Pair<SectionedDataSource, DiffUtil.DiffResult> -> applyDiff(update) })
     }
 }

app/src/main/java/org/tasks/tasklist/HeaderViewHolder.kt

@@ -0,0 +1,73 @@
+package org.tasks.tasklist
+
+import android.content.Context
+import android.view.View
+import android.widget.TextView
+import androidx.annotation.StringRes
+import androidx.recyclerview.widget.RecyclerView
+import com.todoroo.andlib.utility.DateUtilities
+import com.todoroo.astrid.api.Filter
+import com.todoroo.astrid.core.SortHelper
+import org.tasks.R
+import org.tasks.date.DateTimeUtils.newDateTime
+import org.threeten.bp.format.FormatStyle
+import java.util.*
+
+class HeaderViewHolder(
+        private val context: Context,
+        private val locale: Locale,
+        view: View,
+        callback: (Long) -> Unit) : RecyclerView.ViewHolder(view) {
+
+    private val header: TextView = view.findViewById(R.id.header)
+    private var sortGroup = -1L
+
+    fun bind(filter: Filter, sortMode: Int, section: AdapterSection) {
+        sortGroup = section.value
+        val header: String? = if (filter.supportsSorting()) getHeader(sortMode, sortGroup) else null
+
+        if (header == null) {
+            this.header.visibility = View.GONE
+        } else {
+            this.header.visibility = View.VISIBLE
+            this.header.text = header
+            this.header.setCompoundDrawablesRelativeWithIntrinsicBounds(0, 0, if (section.collapsed) R.drawable.ic_keyboard_arrow_up_black_18dp else R.drawable.ic_keyboard_arrow_down_black_18dp, 0)
+            this.header.setTextColor(
+                    context.getColor(
+                            if (sortMode == SortHelper.SORT_DUE && sortGroup > 0 && newDateTime(sortGroup).plusDays(1).startOfDay().isBeforeNow) R.color.overdue else R.color.text_secondary))
+        }
+    }
+
+    private fun getHeader(sortMode: Int, group: Long): String {
+        return when {
+            sortMode == SortHelper.SORT_IMPORTANCE -> context.getString(priorityToString(group.toInt()))
+            group == 0L -> context.getString(if (sortMode == SortHelper.SORT_DUE) {
+                R.string.no_due_date
+            } else {
+                R.string.no_date
+            })
+            sortMode == SortHelper.SORT_CREATED ->
+                context.getString(R.string.sort_created_group, getDateString(group))
+            sortMode == SortHelper.SORT_MODIFIED ->
+                context.getString(R.string.sort_modified_group, getDateString(group))
+            else -> getDateString(group, false)
+        }
+    }
+
+    private fun getDateString(value: Long, lowercase: Boolean = true) =
+            DateUtilities.getRelativeDay(context, value, locale, FormatStyle.FULL, lowercase)
+
+    @StringRes
+    private fun priorityToString(priority: Int) = when (priority) {
+        0 -> R.string.filter_high_priority
+        1 -> R.string.filter_medium_priority
+        2 -> R.string.filter_low_priority
+        else -> R.string.filter_no_priority
+    }
+
+    init {
+        header.setOnClickListener {
+            callback.invoke(sortGroup)
+        }
+    }
+}

app/src/main/java/org/tasks/tasklist/PagedListRecyclerAdapter.kt

@@ -8,6 +8,7 @@ import com.todoroo.astrid.activity.TaskListFragment
 import com.todoroo.astrid.adapter.TaskAdapter
 import com.todoroo.astrid.dao.TaskDao
 import org.tasks.data.TaskContainer
+import org.tasks.preferences.Preferences
 
 class PagedListRecyclerAdapter(
         adapter: TaskAdapter,
@@ -15,7 +16,8 @@ class PagedListRecyclerAdapter(
         viewHolderFactory: ViewHolderFactory,
         taskList: TaskListFragment,
         list: List<TaskContainer>,
-        taskDao: TaskDao) : TaskListRecyclerAdapter(adapter, viewHolderFactory, taskList, taskDao) {
+        taskDao: TaskDao,
+        preferences: Preferences) : TaskListRecyclerAdapter(adapter, viewHolderFactory, taskList, taskDao, preferences) {
 
     private val differ: AsyncPagedListDiffer<TaskContainer> =
             AsyncPagedListDiffer(this, AsyncDifferConfig.Builder(ItemCallback()).build())
@@ -34,6 +36,8 @@ class PagedListRecyclerAdapter(
 
     override fun getItemCount() = differ.itemCount
 
+    override fun getTaskCount() = itemCount
+
     init {
         if (list is PagedList<*>) {
             differ.submitList(list as PagedList<TaskContainer>?)

app/src/main/java/org/tasks/tasklist/SectionedDataSource.kt

@@ -0,0 +1,111 @@
+package org.tasks.tasklist
+
+import android.util.SparseArray
+import com.todoroo.astrid.core.SortHelper
+import org.tasks.data.TaskContainer
+import org.tasks.date.DateTimeUtils
+import java.util.*
+
+class SectionedDataSource constructor(tasks: List<TaskContainer>, disableHeaders: Boolean, val sortMode: Int, private val collapsed: MutableSet<Long>) {
+
+    private val tasks = tasks.toMutableList()
+
+    private val sections = if (disableHeaders) {
+        SparseArray()
+    } else {
+        getSections()
+    }
+
+    fun getItem(position: Int): TaskContainer = tasks[sectionedPositionToPosition(position)]
+
+    fun getHeaderValue(position: Int): Long = sections[position]!!.value
+
+    fun isHeader(position: Int) = sections[position] != null
+
+    private fun sectionedPositionToPosition(sectionedPosition: Int): Int {
+        if (isHeader(sectionedPosition)) {
+            return sections[sectionedPosition].firstPosition
+        }
+
+        var offset = 0
+        for (i in 0 until sections.size()) {
+            val section = sections.valueAt(i)
+            if (section.sectionedPosition > sectionedPosition) {
+                break
+            }
+            --offset
+        }
+        return sectionedPosition + offset
+    }
+
+    val taskCount: Int
+        get() = tasks.size
+
+    val size: Int
+        get() = tasks.size + sections.size()
+
+    fun getSection(position: Int): AdapterSection = sections[position]
+
+    fun add(position: Int, task: TaskContainer) = tasks.add(sectionedPositionToPosition(position), task)
+
+    fun removeAt(position: Int): TaskContainer = tasks.removeAt(sectionedPositionToPosition(position))
+
+    private fun getSections(): SparseArray<AdapterSection> {
+        val sections = ArrayList<AdapterSection>()
+        for (i in tasks.indices) {
+            val task = tasks[i]
+            val sortGroup = task.sortGroup ?: continue
+            val header = if (sortMode == SortHelper.SORT_IMPORTANCE || sortGroup == 0L) {
+                sortGroup
+            } else {
+                DateTimeUtils.newDateTime(sortGroup).startOfDay().millis
+            }
+            val isCollapsed = collapsed.contains(header)
+            if (i == 0) {
+                sections.add(AdapterSection(i, header, 0, isCollapsed))
+            } else {
+                val previous = tasks[i - 1].sortGroup
+                when (sortMode) {
+                    SortHelper.SORT_IMPORTANCE -> if (header != previous) {
+                        sections.add(AdapterSection(i, header, 0, isCollapsed))
+                    }
+                    else -> if (previous > 0 && header != DateTimeUtils.newDateTime(previous).startOfDay().millis) {
+                        sections.add(AdapterSection(i, header, 0, isCollapsed))
+                    }
+                }
+            }
+        }
+
+        var adjustment = 0
+        for (i in sections.indices) {
+            val section = sections[i]
+            section.firstPosition -= adjustment
+            if (section.collapsed) {
+                val next = sections.getOrNull(i + 1)?.firstPosition?.minus(adjustment) ?: tasks.size
+                tasks.subList(section.firstPosition, next).clear()
+                adjustment += next - section.firstPosition
+            }
+        }
+
+        return setSections(sections)
+    }
+
+    private fun setSections(newSections: List<AdapterSection>): SparseArray<AdapterSection> {
+        val sections = SparseArray<AdapterSection>()
+        newSections.forEachIndexed { index, section ->
+            section.sectionedPosition = section.firstPosition + index
+            sections.append(section.sectionedPosition, section)
+        }
+        return sections
+    }
+
+    fun moveSection(toPosition: Int, offset: Int) {
+        val old = sections[toPosition]
+        sections.remove(toPosition)
+        val newSectionedPosition = old.sectionedPosition + offset
+        val previousSection = if (isHeader(newSectionedPosition - 1)) sections[newSectionedPosition - 1] else null
+        val newFirstPosition = previousSection?.firstPosition ?: old.firstPosition + offset
+        val new = AdapterSection(newFirstPosition, old.value, newSectionedPosition, old.collapsed)
+        sections.append(new.sectionedPosition, new)
+    }
+}

app/src/main/java/org/tasks/tasklist/TaskListRecyclerAdapter.kt

@@ -10,22 +10,24 @@ import com.todoroo.astrid.api.Filter
 import com.todoroo.astrid.dao.TaskDao
 import org.tasks.data.TaskContainer
 import org.tasks.intents.TaskIntents
+import org.tasks.preferences.Preferences
 import org.tasks.tasklist.TaskViewHolder.ViewHolderCallbacks
 
 abstract class TaskListRecyclerAdapter internal constructor(
         private val adapter: TaskAdapter,
-        private val viewHolderFactory: ViewHolderFactory,
+        internal val viewHolderFactory: ViewHolderFactory,
         private val taskList: TaskListFragment,
-        private val taskDao: TaskDao) : RecyclerView.Adapter<TaskViewHolder>(), ViewHolderCallbacks, ListUpdateCallback, TaskAdapterDataSource {
+        private val taskDao: TaskDao,
+        internal val preferences: Preferences)
+    : RecyclerView.Adapter<RecyclerView.ViewHolder>(), ViewHolderCallbacks, ListUpdateCallback, TaskAdapterDataSource {
 
-    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): TaskViewHolder {
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder = viewHolderFactory.newViewHolder(parent, this)
-        return viewHolderFactory.newViewHolder(parent, this)
-    }
 
-    override fun onBindViewHolder(holder: TaskViewHolder, position: Int) {
+    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
+        val sortMode = preferences.sortMode
         val task = getItem(position)
         if (task != null) {
-            holder.bindView(task, taskList.getFilter())
+            (holder as TaskViewHolder).bindView(task, taskList.getFilter(), sortMode)
             holder.isMoving = false
             val indent = adapter.getIndent(task)
             task.setIndent(indent)
@@ -85,8 +87,6 @@ abstract class TaskListRecyclerAdapter internal constructor(
 
     protected abstract fun dragAndDropEnabled(): Boolean
 
-    abstract override fun getItem(position: Int): TaskContainer
-
     abstract fun submitList(list: List<TaskContainer>)
 
     override fun onInserted(position: Int, count: Int) {

app/src/main/java/org/tasks/tasklist/TaskViewHolder.java

@@ -1,6 +1,8 @@
 package org.tasks.tasklist;
 
 import static com.todoroo.andlib.utility.DateUtilities.getRelativeDateTime;
+import static com.todoroo.andlib.utility.DateUtilities.getTimeString;
+import static org.tasks.date.DateTimeUtils.newDateTime;
 
 import android.annotation.SuppressLint;
 import android.app.Activity;
@@ -18,13 +20,14 @@ import butterknife.OnLongClick;
 import com.google.android.material.chip.Chip;
 import com.google.android.material.chip.ChipGroup;
 import com.todoroo.astrid.api.Filter;
+import com.todoroo.astrid.core.SortHelper;
 import com.todoroo.astrid.service.TaskCompleter;
 import com.todoroo.astrid.ui.CheckableImageView;
 import java.util.List;
+import java.util.Locale;
 import org.tasks.R;
 import org.tasks.data.TaskContainer;
 import org.tasks.dialogs.Linkify;
-import org.tasks.locale.Locale;
 import org.tasks.preferences.Preferences;
 import org.tasks.ui.CheckBoxProvider;
 import org.tasks.ui.ChipProvider;
@@ -42,6 +45,7 @@ public class TaskViewHolder extends RecyclerView.ViewHolder {
   private final int selectedColor;
   private final int rowPadding;
   private final Linkify linkify;
+  private final Locale locale;
   private final CheckBoxProvider checkBoxProvider;
   private final int textColorOverdue;
   private final ChipProvider chipProvider;
@@ -93,7 +97,8 @@ public class TaskViewHolder extends RecyclerView.ViewHolder {
       int background,
       int selectedColor,
       int rowPadding,
-      Linkify linkify) {
+      Linkify linkify,
+      Locale locale) {
     super(view);
     this.context = context;
     this.preferences = preferences;
@@ -108,6 +113,7 @@ public class TaskViewHolder extends RecyclerView.ViewHolder {
     this.selectedColor = selectedColor;
     this.rowPadding = rowPadding;
     this.linkify = linkify;
+    this.locale = locale;
     ButterKnife.bind(this, view);
 
     if (preferences.getBoolean(R.string.p_fullTaskTitle, false)) {
@@ -188,14 +194,14 @@ public class TaskViewHolder extends RecyclerView.ViewHolder {
     return Math.round(indent * getShiftSize());
   }
 
-  void bindView(TaskContainer task, Filter filter) {
+  void bindView(TaskContainer task, Filter filter, int sortMode) {
     this.task = task;
     this.indent = task.indent;
 
     nameView.setText(task.getTitle());
     hiddenIcon.setVisibility(task.isHidden() ? View.VISIBLE : View.GONE);
     setupTitleAndCheckbox();
-    setupDueDate();
+    setupDueDate(sortMode);
     setupChips(filter);
     if (preferences.getBoolean(R.string.p_show_description, true)) {
       description.setText(task.getNotes());
@@ -233,16 +239,20 @@ public class TaskViewHolder extends RecyclerView.ViewHolder {
     completeBox.invalidate();
   }
 
-  private void setupDueDate() {
+  private void setupDueDate(int sortMode) {
     if (task.hasDueDate()) {
       if (task.isOverdue()) {
         dueDate.setTextColor(textColorOverdue);
       } else {
         dueDate.setTextColor(textColorSecondary);
       }
-      String dateValue =
+      String dateValue;
-          getRelativeDateTime(
+      if (sortMode == SortHelper.SORT_DUE && task.sortGroup != null && newDateTime(task.sortGroup).startOfDay().equals(newDateTime(task.getDueDate()).startOfDay())) {
-              context, task.getDueDate(), Locale.getInstance().getLocale(), FormatStyle.MEDIUM);
+        dateValue =
+            task.hasDueTime() ? getTimeString(context, newDateTime(task.getDueDate())) : null;
+      } else {
+        dateValue = getRelativeDateTime(context, task.getDueDate(), locale, FormatStyle.MEDIUM);
+      }
       dueDate.setText(dateValue);
       dueDate.setVisibility(View.VISIBLE);
     } else {
@@ -332,7 +342,7 @@ public class TaskViewHolder extends RecyclerView.ViewHolder {
     return maxIndent;
   }
 
-  interface ViewHolderCallbacks {
+  public interface ViewHolderCallbacks {
 
     void onCompletedTask(TaskContainer task, boolean newState);
 

app/src/main/java/org/tasks/tasklist/ViewHolderFactory.java

@@ -1,79 +0,0 @@
-package org.tasks.tasklist;
-
-import static com.todoroo.andlib.utility.AndroidUtilities.convertDpToPixels;
-import static org.tasks.preferences.ResourceResolver.getData;
-import static org.tasks.preferences.ResourceResolver.getResourceId;
-
-import android.app.Activity;
-import android.content.Context;
-import android.util.DisplayMetrics;
-import android.view.LayoutInflater;
-import android.view.ViewGroup;
-import com.todoroo.astrid.service.TaskCompleter;
-import javax.inject.Inject;
-import org.tasks.R;
-import org.tasks.dialogs.Linkify;
-import org.tasks.injection.ForActivity;
-import org.tasks.preferences.Preferences;
-import org.tasks.ui.CheckBoxProvider;
-import org.tasks.ui.ChipProvider;
-
-public class ViewHolderFactory {
-
-  private final int textColorSecondary;
-  private final int textColorOverdue;
-  private final Context context;
-  private final ChipProvider chipProvider;
-  private final int fontSize;
-  private final CheckBoxProvider checkBoxProvider;
-  private final TaskCompleter taskCompleter;
-  private final DisplayMetrics metrics;
-  private final int background;
-  private final int selectedColor;
-  private final int rowPadding;
-  private final Linkify linkify;
-  private final Preferences preferences;
-
-  @Inject
-  public ViewHolderFactory(
-      @ForActivity Context context,
-      Preferences preferences,
-      ChipProvider chipProvider,
-      CheckBoxProvider checkBoxProvider,
-      TaskCompleter taskCompleter,
-      Linkify linkify) {
-    this.context = context;
-    this.chipProvider = chipProvider;
-    this.checkBoxProvider = checkBoxProvider;
-    this.taskCompleter = taskCompleter;
-    this.preferences = preferences;
-    this.linkify = linkify;
-    textColorSecondary = getData(context, android.R.attr.textColorSecondary);
-    textColorOverdue = context.getColor(R.color.overdue);
-    background = getResourceId(context, R.attr.selectableItemBackground);
-    selectedColor = getData(context, R.attr.colorControlHighlight);
-    fontSize = preferences.getFontSize();
-    metrics = context.getResources().getDisplayMetrics();
-    rowPadding = convertDpToPixels(metrics, preferences.getInt(R.string.p_rowPadding, 16));
-  }
-
-  TaskViewHolder newViewHolder(ViewGroup parent, TaskViewHolder.ViewHolderCallbacks callbacks) {
-    return new TaskViewHolder(
-        (Activity) context,
-        (ViewGroup)
-            LayoutInflater.from(context).inflate(R.layout.task_adapter_row, parent, false),
-        preferences,
-        fontSize,
-        chipProvider,
-        checkBoxProvider,
-        textColorOverdue,
-        textColorSecondary,
-        taskCompleter,
-        callbacks,
-        metrics,
-        background,
-        selectedColor,
-        rowPadding,
-        linkify);
-  }
-}

app/src/main/java/org/tasks/tasklist/ViewHolderFactory.kt

@@ -0,0 +1,62 @@
+package org.tasks.tasklist
+
+import android.app.Activity
+import android.content.Context
+import android.util.DisplayMetrics
+import android.view.LayoutInflater
+import android.view.ViewGroup
+import com.todoroo.andlib.utility.AndroidUtilities
+import com.todoroo.astrid.service.TaskCompleter
+import org.tasks.R
+import org.tasks.dialogs.Linkify
+import org.tasks.injection.ForActivity
+import org.tasks.preferences.Preferences
+import org.tasks.preferences.ResourceResolver
+import org.tasks.tasklist.TaskViewHolder.ViewHolderCallbacks
+import org.tasks.ui.CheckBoxProvider
+import org.tasks.ui.ChipProvider
+import java.util.*
+import javax.inject.Inject
+
+class ViewHolderFactory @Inject constructor(
+        @param:ForActivity private val context: Context,
+        private val preferences: Preferences,
+        private val chipProvider: ChipProvider,
+        private val checkBoxProvider: CheckBoxProvider,
+        private val taskCompleter: TaskCompleter,
+        private val linkify: Linkify,
+        private val locale: Locale) {
+    private val textColorSecondary: Int = ResourceResolver.getData(context, android.R.attr.textColorSecondary)
+    private val textColorOverdue: Int = context.getColor(R.color.overdue)
+    private val fontSize: Int = preferences.fontSize
+    private val metrics: DisplayMetrics = context.resources.displayMetrics
+    private val background: Int = ResourceResolver.getResourceId(context, R.attr.selectableItemBackground)
+    private val selectedColor: Int = ResourceResolver.getData(context, R.attr.colorControlHighlight)
+    private val rowPadding: Int = AndroidUtilities.convertDpToPixels(metrics, preferences.getInt(R.string.p_rowPadding, 16))
+
+    fun newHeaderViewHolder(parent: ViewGroup?, callback: (Long) -> Unit) =
+            HeaderViewHolder(
+                    context,
+                    locale,
+                    LayoutInflater.from(context).inflate(R.layout.task_adapter_header, parent, false),
+                    callback)
+
+    fun newViewHolder(parent: ViewGroup?, callbacks: ViewHolderCallbacks?) =
+            TaskViewHolder(
+                    context as Activity,
+                    LayoutInflater.from(context).inflate(R.layout.task_adapter_row, parent, false) as ViewGroup,
+                    preferences,
+                    fontSize,
+                    chipProvider,
+                    checkBoxProvider,
+                    textColorOverdue,
+                    textColorSecondary,
+                    taskCompleter,
+                    callbacks,
+                    metrics,
+                    background,
+                    selectedColor,
+                    rowPadding,
+                    linkify,
+                    locale)
+}

app/src/main/res/layout/task_adapter_header.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<TextView xmlns:android="http://schemas.android.com/apk/res/android"
+  xmlns:app="http://schemas.android.com/apk/res-auto"
+  android:id="@+id/header"
+  style="@style/TextAppearance"
+  android:layout_width="match_parent"
+  android:layout_height="wrap_content"
+  android:background="?attr/selectableItemBackground"
+  android:padding="@dimen/keyline_first"
+  android:gravity="start|center_vertical"
+  android:textColor="@color/text_secondary"
+  android:textSize="@dimen/sku_details_row_text_size"
+  android:drawableEnd="@drawable/ic_keyboard_arrow_down_black_18dp"
+  android:drawableTint="@color/text_tertiary"
+  app:fontFamily="sans-serif-medium" />
+

app/src/main/res/values/strings.xml

@@ -630,4 +630,6 @@ File %1$s contained %2$s.\n\n
   <string name="support_development_subscribe">Unlock additional features and support open source software</string>
   <string name="no_thanks">No thanks</string>
   <string name="got_it">Got it!</string>
+  <string name="sort_created_group">Created %s</string>
+  <string name="sort_modified_group">Modified %s</string>
 </resources>