[UI] Enable colored app bars on scroll (#211)

* Extract fragment scroll listener to separate file

* Replace canRefresh with isScrolled

* Add empty helper class to animate app bar color

* Implement AppBarColorAnimator

* Rename getRefreshScrollingView() to getScrollingView()

* Set isScrolled on drag start

* Clear isScrolled on fling to top

* Add getSyncParams() to fragments

* Convert getAppBars() to property

* Tint TabLayout background drawable

Author: kuba2k2

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/agenda/AgendaFragment.kt

@@ -19,6 +19,7 @@ import kotlinx.coroutines.withContext
 import pl.szczodrzynski.edziennik.MainActivity
 import pl.szczodrzynski.edziennik.R
 import pl.szczodrzynski.edziennik.data.db.entity.Profile
+import pl.szczodrzynski.edziennik.data.enums.FeatureType
 import pl.szczodrzynski.edziennik.data.enums.MetadataType
 import pl.szczodrzynski.edziennik.databinding.FragmentAgendaCalendarBinding
 import pl.szczodrzynski.edziennik.databinding.FragmentAgendaDefaultBinding
@@ -45,6 +46,7 @@ class AgendaFragment : BaseFragment<ViewBinding, MainActivity>(
 
     override fun getFab() = R.string.add to CommunityMaterial.Icon3.cmd_plus
     override fun getMarkAsReadType() = MetadataType.EVENT
+    override fun getSyncParams() = FeatureType.AGENDA to null
     override fun getBottomSheetItems() = listOf(
         BottomSheetPrimaryItem(true)
             .withTitle(R.string.menu_add_event)
@@ -114,6 +116,7 @@ class AgendaFragment : BaseFragment<ViewBinding, MainActivity>(
     private suspend fun createDefaultAgendaView(b: FragmentAgendaDefaultBinding) {
         if (!isAdded)
             return
+        canRefreshDisabled = true
         checkEventTypes()
         delay(500)
 

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/attendance/AttendanceFragment.kt

@@ -7,6 +7,7 @@ package pl.szczodrzynski.edziennik.ui.attendance
 import com.mikepenz.iconics.typeface.library.community.material.CommunityMaterial
 import pl.szczodrzynski.edziennik.MainActivity
 import pl.szczodrzynski.edziennik.R
+import pl.szczodrzynski.edziennik.data.enums.FeatureType
 import pl.szczodrzynski.edziennik.data.enums.MetadataType
 import pl.szczodrzynski.edziennik.databinding.BasePagerFragmentBinding
 import pl.szczodrzynski.edziennik.ext.Bundle
@@ -32,6 +33,7 @@ class AttendanceFragment : PagerFragment<BasePagerFragmentBinding, MainActivity>
         }
 
     override fun getMarkAsReadType() = MetadataType.ATTENDANCE
+    override fun getSyncParams() = FeatureType.ATTENDANCE to null
     override fun getBottomSheetItems() = listOf(
         BottomSheetPrimaryItem(true)
             .withTitle(R.string.menu_attendance_config)

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/attendance/AttendanceListFragment.kt

@@ -29,7 +29,7 @@ class AttendanceListFragment : BaseFragment<AttendanceListFragmentBinding, MainA
     inflater = AttendanceListFragmentBinding::inflate,
 ) {
 
-    override fun getRefreshScrollingView() = b.list
+    override fun getScrollingView() = b.list
 
     private var viewType = AttendanceFragment.VIEW_DAYS
     private var expandSubjectId = 0L

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/attendance/AttendanceSummaryFragment.kt

@@ -43,7 +43,7 @@ class AttendanceSummaryFragment : BaseFragment<AttendanceSummaryFragmentBinding,
         private var periodSelection = 0
     }
 
-    override fun getRefreshScrollingView() = b.scrollView
+    override fun getScrollingView() = b.scrollView
 
     private val manager
         get() = app.attendanceManager

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/base/fragment/ActivityUtil.kt

@@ -4,11 +4,7 @@
 
 package pl.szczodrzynski.edziennik.ui.base.fragment
 
-import android.annotation.SuppressLint
-import android.view.MotionEvent
-import android.view.View
 import android.widget.Toast
-import androidx.recyclerview.widget.RecyclerView
 import com.mikepenz.iconics.typeface.library.community.material.CommunityMaterial
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
@@ -18,49 +14,6 @@ import pl.szczodrzynski.edziennik.ui.login.LoginActivity
 import pl.szczodrzynski.navlib.bottomsheet.items.BottomSheetPrimaryItem
 import pl.szczodrzynski.navlib.bottomsheet.items.BottomSheetSeparatorItem
 
-@SuppressLint("ClickableViewAccessibility")
-internal fun BaseFragment<*, *>.setupCanRefresh() {
-    when (val view = getRefreshScrollingView()) {
-        is RecyclerView -> {
-            canRefresh = !view.canScrollVertically(-1)
-            view.addOnScrollListener(object : RecyclerView.OnScrollListener() {
-                override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
-                    // disable refresh when scrolled down
-                    if (recyclerView.canScrollVertically(-1))
-                        canRefresh = false
-                    // enable refresh when scrolled to the top and not scrolling anymore
-                    else if (newState == RecyclerView.SCROLL_STATE_IDLE)
-                        canRefresh = true
-                }
-            })
-        }
-
-        is View -> {
-            canRefresh = !view.canScrollVertically(-1)
-            var isTouched = false
-            view.setOnTouchListener { _, event ->
-                // keep track of the touch state
-                when (event.action) {
-                    MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> isTouched = false
-                    MotionEvent.ACTION_DOWN, MotionEvent.ACTION_MOVE -> isTouched = true
-                }
-                // disable refresh when scrolled down
-                if (view.canScrollVertically(-1))
-                    canRefresh = false
-                // enable refresh when scrolled to the top and not touching anymore
-                else if (!isTouched)
-                    canRefresh = true
-                false
-            }
-        }
-
-        else -> {
-            // dispatch the default value to the activity
-            canRefresh = canRefresh
-        }
-    }
-}
-
 internal fun BaseFragment<*, *>.setupMainActivity(activity: MainActivity) {
     val items = getBottomSheetItems().toMutableList()
     getMarkAsReadType()?.let { metadataType ->
@@ -97,6 +50,8 @@ internal fun BaseFragment<*, *>.setupMainActivity(activity: MainActivity) {
             }
         }
     }
+
+    appBars += activity.navView.toolbar
 }
 
 internal fun BaseFragment<*, *>.setupLoginActivity(activity: LoginActivity) {}

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/base/fragment/BaseFragment.kt

@@ -12,13 +12,15 @@ import android.view.ViewGroup
 import androidx.appcompat.app.AppCompatActivity
 import androidx.fragment.app.Fragment
 import androidx.viewbinding.ViewBinding
+import com.google.gson.JsonObject
 import com.mikepenz.iconics.typeface.IIcon
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
 import org.greenrobot.eventbus.EventBus
 import pl.szczodrzynski.edziennik.App
 import pl.szczodrzynski.edziennik.MainActivity
+import pl.szczodrzynski.edziennik.data.enums.FeatureType
 import pl.szczodrzynski.edziennik.data.enums.MetadataType
 import pl.szczodrzynski.edziennik.ext.registerSafe
 import pl.szczodrzynski.edziennik.ext.startCoroutineTimer
@@ -38,31 +40,37 @@ abstract class BaseFragment<B : ViewBinding, A : AppCompatActivity>(
 
     private var isViewReady: Boolean = false
     private var inState: Bundle? = null
+    private var appBarAnimator: AppBarColorAnimator? = null
 
     /**
-     * Enables or disables the activity's SwipeRefreshLayout.
-     * Use only if [getRefreshScrollingView] is not used.
-     *
-     * The [PagerFragment] manages its [canRefresh] state
-     * based on the value of the currently selected page.
+     * Whether the view is currently being scrolled
+     * or is left scrolled away from the top.
      */
-    internal var canRefresh = false
-        set(value) {
+    internal var isScrolled = false
+        set(value) { // cannot be private - PagerFragment onPageScrollStateChanged
             field = value
-            (activity as? MainActivity)?.swipeRefreshLayout?.isEnabled =
-                !canRefreshDisabled && value
+            dispatchCanRefresh()
+            appBarAnimator?.dispatchLiftOnScroll()
         }
 
     /**
-     * Forcefully disables the activity's SwipeRefreshLayout
-     * if [getRefreshScrollingView] is used.
+     * Forcefully disables the activity's SwipeRefreshLayout.
+     *
+     * The [PagerFragment] manages its [canRefreshDisabled] state
+     * based on the value of the currently selected page.
      */
     internal var canRefreshDisabled = false
         set(value) {
             field = value
-            canRefresh = canRefresh
+            dispatchCanRefresh()
         }
 
+    /**
+     * A list of views (usually app bars) that should have their
+     * background color elevated when the fragment is scrolled.
+     */
+    internal var appBars = mutableSetOf<View>()
+
     private var job = Job()
     final override val coroutineContext: CoroutineContext
         get() = job + Dispatchers.Main
@@ -83,6 +91,7 @@ abstract class BaseFragment<B : ViewBinding, A : AppCompatActivity>(
             ?: return null
         isViewReady = false // reinitialize the view in onResume()
         inState = savedInstanceState // save the instance state for onResume()
+        appBarAnimator = AppBarColorAnimator(activity, appBars)
         return b.root
     }
 
@@ -92,9 +101,17 @@ abstract class BaseFragment<B : ViewBinding, A : AppCompatActivity>(
         if (!isAdded || isViewReady)
             return
         isViewReady = true
-        setupCanRefresh()
+        // setup the activity (bottom sheet, FAB, etc.)
+        // run before setupScrollListener {} to populate appBars
         (activity as? MainActivity)?.let(::setupMainActivity)
         (activity as? LoginActivity)?.let(::setupLoginActivity)
+        // listen to scroll state changes
+        var first = true
+        setupScrollListener {
+            if (isScrolled != it || first)
+                isScrolled = it
+            first = false
+        }
         // let the UI transition for a moment
         startCoroutineTimer(100L) {
             if (!isAdded)
@@ -141,9 +158,10 @@ abstract class BaseFragment<B : ViewBinding, A : AppCompatActivity>(
 
     /**
      * Called to retrieve the scrolling view contained in the fragment.
-     * The scrolling view is configured to act nicely with the SwipeRefreshLayout.
+     * The scrolling view is configured to work nicely with the app bars
+     * and the SwipeRefreshLayout.
      */
-    open fun getRefreshScrollingView(): View? = null
+    open fun getScrollingView(): View? = null
 
     /**
      * Called to retrieve the FAB label resource and the icon.
@@ -157,6 +175,22 @@ abstract class BaseFragment<B : ViewBinding, A : AppCompatActivity>(
      */
     open fun getMarkAsReadType(): MetadataType? = null
 
+    /**
+     * Called to retrieve the [FeatureType] this fragment is associated with.
+     * May also return arguments for the sync task.
+     *
+     * If not provided, swipe-to-refresh is disabled and the manual sync dialog
+     * selects all features by default.
+     *
+     * If [FeatureType] is null, all features are synced (and selected by the
+     * manual sync dialog).
+     *
+     * It is important to return the desired [FeatureType] from the first
+     * call of this method, which runs before [onViewReady]. Otherwise,
+     * swipe-to-refresh will not be enabled unless the view is scrolled.
+     */
+    open fun getSyncParams(): Pair<FeatureType?, JsonObject?>? = null
+
     /**
      * Called to retrieve any extra bottom sheet items that should be displayed.
      */

Diff for: app/src/main/java/pl/szczodrzynski/edziennik/ui/base/fragment/PagerFragment.kt

@@ -23,8 +23,8 @@ abstract class PagerFragment<B : ViewBinding, A : AppCompatActivity>(
     inflater: ((inflater: LayoutInflater, parent: ViewGroup?, attachToParent: Boolean) -> B)?,
 ) : BaseFragment<B, A>(inflater) {
 
-    private lateinit var pages: List<Pair<Fragment, String>>
-    private val fragmentCache = mutableMapOf<Int, Fragment>()
+    private lateinit var pages: List<Pair<BaseFragment<*, *>, String>>
+    private val fragmentCache = mutableMapOf<Int, BaseFragment<*, *>>()
 
     /**
      * Stores the default page index that is activated when
@@ -37,6 +37,18 @@ abstract class PagerFragment<B : ViewBinding, A : AppCompatActivity>(
      */
     protected open var savedPageSelection = -1
 
+    protected val currentFragment: BaseFragment<*, *>?
+        get() = fragmentCache[getViewPager().currentItem]
+
+    final override fun getScrollingView() = null
+    override fun getSyncParams() = currentFragment?.getSyncParams()
+
+    override fun onResume() {
+        // add TabLayout before super's setupScrollListener {}
+        appBars += getTabLayout()
+        super.onResume()
+    }
+
     override suspend fun onViewReady(savedInstanceState: Bundle?) {
         if (savedPageSelection == -1)
             savedPageSelection = savedInstanceState?.getInt("pageSelection") ?: 0
@@ -47,6 +59,7 @@ abstract class PagerFragment<B : ViewBinding, A : AppCompatActivity>(
             override fun getItemCount() = getPageCount()
             override fun createFragment(position: Int): Fragment {
                 val fragment = getPageFragment(position)
+                fragment.appBars += getTabLayout()
                 fragmentCache[position] = fragment
                 return fragment
             }
@@ -58,15 +71,15 @@ abstract class PagerFragment<B : ViewBinding, A : AppCompatActivity>(
             it.setCurrentItem(savedPageSelection, false)
             it.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
                 override fun onPageScrollStateChanged(state: Int) {
-                    canRefresh = when (state) {
-                        ViewPager2.SCROLL_STATE_IDLE -> {
-                            val fragment =
-                                fragmentCache[it.currentItem] as? BaseFragment<*, *>
-                            fragment != null && !fragment.canRefreshDisabled && fragment.canRefresh
-                        }
-
-                        else -> false
+                    if (state != ViewPager2.SCROLL_STATE_IDLE) {
+                        // disable swipe-to-refresh during scrolling
+                        canRefreshDisabled = true
+                        return
                     }
+                    // take child fragment's values
+                    val fragment = currentFragment
+                    canRefreshDisabled = fragment?.canRefreshDisabled == true
+                    isScrolled = fragment?.isScrolled == true
                 }
 
                 override fun onPageSelected(position: Int) {
@@ -125,7 +138,7 @@ abstract class PagerFragment<B : ViewBinding, A : AppCompatActivity>(
      * Only used with the default implementation of [getPageCount], [getPageFragment]
      * and [getPageTitle].
      */
-    open suspend fun onCreatePages() = listOf<Pair<Fragment, String>>()
+    open suspend fun onCreatePages() = listOf<Pair<BaseFragment<*, *>, String>>()
 
     open fun getPageCount() = pages.size
     open fun getPageFragment(position: Int) = pages[position].first