Scroll dash profile title off-screen with the app grid

AGENTS.md

@@ -93,7 +93,25 @@ etc/                                        — design assets (SVG/XCF sources,
     (the genie) and `ThemeApplier` reach the live grid (both null-safe for when
     it isn't laid out yet). The per-page `LayoutTransition` is set in the adapter
     (it can't be in `LayoutTransitionConfigurer`, which runs before any page
-    exists). Tests force the lazy layout via `ActivityTestSupport.layoutDashApps`.
+    exists) and **must** keep `setAnimateParentHierarchy(false)`: ViewPager2
+    rejects a page whose child ViewGroup has a parent-animating LayoutTransition
+    and crashes mid-scroll (notably on rotation). Each page's title
+    (`tvDashHomeTitle` — the profile name, or "Applications" for a single
+    profile) overlays the top of its grid rather than sitting in a row above it:
+    the grid reserves a top padding the height of the title (`clipToPadding=false`
+    so that padding scrolls away with the apps) and
+    `ProfilePagerAdapter.updateTitleOffset` translates the title up in step with
+    the grid's scroll, so it scrolls off-screen with the first row instead of
+    permanently occupying the top of the dash. The padding is applied in
+    `onBindViewHolder` *before* the grid's adapter is set (from a one-off
+    `measureTitleHeight`, stable since the title is one line of identical height
+    for every profile): AbsListView does not re-anchor already-filled rows when
+    paddingTop changes at runtime, so applying it after the fill left the first
+    row at `top=0` and the title resting pre-collapsed on swiped-to pages. A grid
+    layout-change listener recomputes the at-rest offset after any (re)fill or
+    rotation, since the scroll listener never fires for a page whose apps fit
+    without scrolling.
+    Tests force the lazy layout via `ActivityTestSupport.layoutDashApps`.
     Grid sizing is owned by `desktop/dash/DashGrid` (the dash counterpart to
     `widgets/WidgetGrid`): the user picks a column count across the short screen
     edge (`DASH_GRID_COLUMNS`, adaptive default from `smallestScreenWidthDp`),

app/src/main/java/be/robinj/distrohopper/desktop/dash/ProfilePagerAdapter.kt

@@ -5,6 +5,7 @@ import android.os.UserHandle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.widget.AbsListView
 import android.widget.GridView
 import android.widget.TextView
 import androidx.recyclerview.widget.RecyclerView
@@ -45,15 +46,76 @@ class ProfilePagerAdapter(
 
 		// The icon appear/disappear transition that LayoutTransitionConfigurer
 		// used to set on the standalone grid; set per page here since the pages
-		// don't exist when that configurer runs.
+		// don't exist when that configurer runs. setAnimateParentHierarchy(false)
+		// is required: ViewPager2 rejects a page whose child ViewGroup has a
+		// LayoutTransition that animates the parent hierarchy (the default), and
+		// crashes mid-scroll on the next layout pass (e.g. on rotation) with
+		// "...interferes with the scrolling animation".
 		holder.grid.layoutTransition = LayoutTransition().apply {
 			setDuration(180L)
 			setStartDelay(LayoutTransition.APPEARING, 0)
+			setAnimateParentHierarchy(false)
 		}
 
+		this.bindTitleCollapse(holder)
+
 		return holder
 	}
 
+	/**
+	 * Makes the page title scroll off-screen together with the apps instead of
+	 * staying pinned above them. The title overlays the grid's top padding (see
+	 * widget_dash_profile_page) and we translate it up in step with the grid's
+	 * scroll, so it slides out of view as the first row of apps does.
+	 *
+	 * The padding that reserves the title's space is set in onBindViewHolder
+	 * *before* the grid's adapter (so the first fill lands the first row at
+	 * paddingTop); it must not change after the grid is populated, because
+	 * AbsListView does not re-anchor already-laid-out rows when paddingTop
+	 * changes at runtime (that was the cause of the title resting pre-collapsed
+	 * on swiped-to pages). Here we only attach the listeners that read the
+	 * scroll position and move the title:
+	 *  - a scroll listener for live scrolling, and
+	 *  - a layout-change listener so the at-rest baseline is recomputed after
+	 *    any (re)fill or rotation — the scroll listener never fires for a page
+	 *    whose apps fit without scrolling. Both only set translationY, which is
+	 *    a draw-time transform, so they don't trigger further layout.
+	 */
+	private fun bindTitleCollapse(holder: PageViewHolder) {
+		holder.grid.addOnLayoutChangeListener { _, _, _, _, _, _, _, _, _ ->
+			this.updateTitleOffset(holder)
+		}
+
+		holder.grid.setOnScrollListener(object : AbsListView.OnScrollListener {
+			override fun onScrollStateChanged(view: AbsListView, scrollState: Int) {}
+			override fun onScroll(view: AbsListView, firstVisibleItem: Int,
+				visibleItemCount: Int, totalItemCount: Int) {
+				this@ProfilePagerAdapter.updateTitleOffset(holder)
+			}
+		})
+	}
+
+	private fun updateTitleOffset(holder: PageViewHolder) {
+		// The reserved space (== title height) is the grid's top padding; the
+		// title is fully off-screen once scrolled by that much.
+		val collapse = holder.grid.paddingTop
+		if (collapse == 0) {
+			holder.title.translationY = 0F
+			return
+		}
+
+		// With the padding applied before the fill, the first row rests at
+		// paddingTop; as the grid scrolls up that gap shrinks. Once the first
+		// row has scrolled past the top the title is fully gone.
+		val first = holder.grid.getChildAt(0)
+		val scrolled = if (holder.grid.firstVisiblePosition == 0 && first != null) {
+			collapse - first.top
+		} else {
+			collapse
+		}
+		holder.title.translationY = -scrolled.coerceIn(0, collapse).toFloat()
+	}
+
 	override fun getItemCount(): Int = this.profiles.size
 
 	override fun onBindViewHolder(holder: PageViewHolder, position: Int) {
@@ -70,9 +132,37 @@ class ProfilePagerAdapter(
 		holder.title.setShadowLayer(5F, 2F, 2F,
 			res.getColor(theme.dash_applauncher_text_shadow_colour))
 
+		// Reserve the title's space as grid top padding *before* assigning the
+		// adapter, so the very first fill of this page lands the first row at
+		// paddingTop. Changing padding after the grid is populated does not move
+		// already-laid-out rows, which left the title pre-collapsed on swiped-to
+		// pages. The title is a single line of identical height for every
+		// profile, so a one-off measure is stable across pages.
+		val titleHeight = this.measureTitleHeight(holder.title)
+		if (holder.grid.paddingTop != titleHeight) {
+			holder.grid.setPadding(holder.grid.paddingLeft, titleHeight,
+				holder.grid.paddingRight, holder.grid.paddingBottom)
+		}
+
 		holder.grid.adapter = this.gridAdapters[position]
 		holder.grid.onItemClickListener = AppLauncherClickListener(this.activity)
 		holder.grid.onItemLongClickListener = AppLauncherLongClickListener(this.activity)
+
+		// Fresh bind starts at scroll 0; reset the baseline so a recycled holder
+		// doesn't carry a previous (scrolled) page's translation. The layout
+		// listener corrects it once this page's rows are laid out.
+		holder.title.translationY = 0F
+	}
+
+	/**
+	 * The laid-out height of the single-line title, measured without needing the
+	 * view to be attached/laid out yet, so it can be reserved as grid padding
+	 * before the first fill.
+	 */
+	private fun measureTitleHeight(title: TextView): Int {
+		val unspecified = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED)
+		title.measure(unspecified, unspecified)
+		return title.measuredHeight
 	}
 
 	override fun onViewAttachedToWindow(holder: PageViewHolder) {

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

@@ -4,28 +4,34 @@
      The grid carries the gvDashHomeApps id so the genie animation, layout
      transition and icon-width theming resolve the current page (only the
      current page is attached when the pager is idle). The title swipes with the
-     page: the profile name, or "Applications" when there is a single profile. -->
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="match_parent"
-    android:layout_height="match_parent"
-    android:orientation="vertical">
+     page: the profile name, or "Applications" when there is a single profile.
 
-    <TextView
-        android:id="@+id/tvDashHomeTitle"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:layout_gravity="center_horizontal"
-        android:textAppearance="@style/textshadow_2px_black"
-        android:textColor="@android:color/white" />
+     The title overlays the top of the grid rather than sitting in a row above
+     it: the grid keeps a top padding the height of the title (clipToPadding is
+     false so that padding scrolls away with the content), and
+     ProfilePagerAdapter translates the title in step with the grid's scroll. So
+     the title scrolls off-screen together with the apps instead of permanently
+     occupying the top of the dash. -->
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
 
     <GridView
         android:id="@+id/gvDashHomeApps"
         android:layout_width="match_parent"
-        android:layout_height="0dp"
-        android:layout_weight="1"
+        android:layout_height="match_parent"
         android:choiceMode="singleChoice"
+        android:clipToPadding="false"
         android:columnWidth="@dimen/dash_applauncher_width"
         android:gravity="center"
         android:numColumns="auto_fit"
         android:scrollbars="none" />
-</LinearLayout>
+
+    <TextView
+        android:id="@+id/tvDashHomeTitle"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center_horizontal"
+        android:textAppearance="@style/textshadow_2px_black"
+        android:textColor="@android:color/white" />
+</FrameLayout>