feat: scroll app list from anywhere on screen; gate search item animation

DrawFragment: app-list touch area now forwards vertical drags/flings to the
drawer RecyclerView, so the list scrolls even when grabbing empty space
right of the app names. OnSwipeTouchListener gained no-op vertical scroll
and fling hooks.

When animations are disabled, drop the RecyclerView item animator so
DiffUtil search updates no longer pan entries up into place.

app/src/main/java/com/github/droidworksstudio/launcher/listener/OnSwipeTouchListener.kt

@@ -90,6 +90,7 @@ internal open class OnSwipeTouchListener(context: Context?, private val preferen
                 }
                 // Vertical swipe
                 else {
+                    onVerticalScroll(distanceY)
                     if (abs(diffY) > swipeThreshold && abs(distanceY) > swipeScrollThreshold) {
                         if (diffY > 0) onSwipeDown() else onSwipeUp()
                     }
@@ -115,6 +116,7 @@ internal open class OnSwipeTouchListener(context: Context?, private val preferen
                     }
                 } else {
                     if (abs(diffY) > swipeThreshold && abs(velocityY) > swipeVelocityThreshold) {
+                        onVerticalFling(velocityY)
                         if (diffY < 0) onSwipeUp() else onSwipeDown()
                     }
                 }
@@ -129,6 +131,21 @@ internal open class OnSwipeTouchListener(context: Context?, private val preferen
     open fun onSwipeLeft() {}
     open fun onSwipeUp() {}
     open fun onSwipeDown() {}
+
+    /**
+     * Called for every vertical drag movement (per-event delta, same sign
+     * convention as RecyclerView's own touch handling: positive when the
+     * finger moves up). Default is a no-op.
+     */
+    open fun onVerticalScroll(distanceY: Float) {}
+
+    /**
+     * Called on a vertical fling with the raw pointer velocity in pixels per
+     * second (positive when the finger moved down, same convention as
+     * VelocityTracker.getYVelocity()). Default is a no-op.
+     */
+    open fun onVerticalFling(velocityY: Float) {}
+
     open fun onLongClick() {}
     open fun onDoubleClick() {}
     open fun onTripleClick() {}

app/src/main/java/com/github/droidworksstudio/launcher/ui/drawer/DrawFragment.kt

@@ -40,6 +40,7 @@ import com.github.droidworksstudio.launcher.helper.PreferenceHelper
 import com.github.droidworksstudio.launcher.listener.OnItemClickedListener
 import com.github.droidworksstudio.launcher.listener.OnSwipeTouchListener
 import com.github.droidworksstudio.launcher.listener.ScrollEventListener
+import kotlin.math.roundToInt
 import com.github.droidworksstudio.launcher.ui.bottomsheetdialog.AppInfoBottomSheetFragment
 import com.github.droidworksstudio.launcher.utils.Constants
 import com.github.droidworksstudio.launcher.viewmodel.AppViewModel
@@ -157,6 +158,11 @@ class DrawFragment : Fragment(),
             setHasFixedSize(false)
             layoutManager = StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL)
             isNestedScrollingEnabled = false
+
+            // Search results update the list with DiffUtil. When animations
+            // are disabled, drop the item animator so entries don't "pan-up"
+            // into place while filtering.
+            if (preferenceHelper.disableAnimations) itemAnimator = null
         }
     }
 
@@ -237,7 +243,7 @@ class DrawFragment : Fragment(),
         binding.apply {
             mainView.setOnTouchListener(getSwipeGestureListener(context))
             touchArea.setOnTouchListener(getSwipeGestureListener(context))
-            appListTouchArea.setOnTouchListener(getSwipeGestureListener(context))
+            appListTouchArea.setOnTouchListener(getAppListSwipeGestureListener(context))
         }
     }
 
@@ -302,36 +308,65 @@ class DrawFragment : Fragment(),
         return object : OnSwipeTouchListener(context, preferenceHelper) {
             override fun onSwipeLeft() {
                 super.onSwipeLeft()
-                val actionTypeNavOptions: NavOptions? =
-                    if (preferenceHelper.disableAnimations) null
-                    else appHelper.getActionType(Constants.Swipe.Left)
-
-                Handler(Looper.getMainLooper()).post {
-                    findNavController().navigate(
-                        R.id.HomeFragment,
-                        null,
-                        actionTypeNavOptions
-                    )
-                }
+                navigateToHome(Constants.Swipe.Left)
             }
 
             override fun onSwipeRight() {
                 super.onSwipeRight()
-                val actionTypeNavOptions: NavOptions? =
-                    if (preferenceHelper.disableAnimations) null
-                    else appHelper.getActionType(Constants.Swipe.Right)
-
-                Handler(Looper.getMainLooper()).post {
-                    findNavController().navigate(
-                        R.id.HomeFragment,
-                        null,
-                        actionTypeNavOptions
-                    )
-                }
+                navigateToHome(Constants.Swipe.Right)
             }
         }
     }
 
+    /**
+     * Swipe listener for the app list area.
+     *
+     * Behaves like [getSwipeGestureListener] (left/right swipes navigate
+     * home), but vertical drags and flings over the empty space around the
+     * list (e.g. right of the app names) scroll the list itself. This makes
+     * the drawer scrollable from the whole screen, not just the app rows.
+     */
+    private fun getAppListSwipeGestureListener(context: Context): View.OnTouchListener {
+        return object : OnSwipeTouchListener(context, preferenceHelper) {
+            override fun onSwipeLeft() {
+                super.onSwipeLeft()
+                navigateToHome(Constants.Swipe.Left)
+            }
+
+            override fun onSwipeRight() {
+                super.onSwipeRight()
+                navigateToHome(Constants.Swipe.Right)
+            }
+
+            override fun onVerticalScroll(distanceY: Float) {
+                super.onVerticalScroll(distanceY)
+                binding.drawAdapter.scrollBy(0, distanceY.roundToInt())
+            }
+
+            override fun onVerticalFling(velocityY: Float) {
+                super.onVerticalFling(velocityY)
+                // RecyclerView.fling expects the negated pointer velocity
+                // (the same negation RecyclerView applies to its own
+                // VelocityTracker value in onTouchEvent).
+                binding.drawAdapter.fling(0, -velocityY.roundToInt())
+            }
+        }
+    }
+
+    private fun navigateToHome(swipe: Constants.Swipe) {
+        val actionTypeNavOptions: NavOptions? =
+            if (preferenceHelper.disableAnimations) null
+            else appHelper.getActionType(swipe)
+
+        Handler(Looper.getMainLooper()).post {
+            findNavController().navigate(
+                R.id.HomeFragment,
+                null,
+                actionTypeNavOptions
+            )
+        }
+    }
+
     /**
      * Runs the fuzzy search synchronously over the in-memory index.
      *