[material_ui] Paint Scaffold persistent bottom sheet background color behind the keyboard

packages/material_ui/lib/src/scaffold.dart

@@ -983,6 +983,46 @@ class _BodyBoxConstraints extends BoxConstraints {
       Object.hash(super.hashCode, materialBannerHeight, bottomWidgetsHeight, appBarHeight);
 }
 
+// Used to communicate the keyboard inset computed by _ScaffoldLayout to the
+// persistent bottom sheet, in the same way _BodyBoxConstraints communicates
+// layout information to the body.
+class _BottomSheetBoxConstraints extends BoxConstraints {
+  const _BottomSheetBoxConstraints({super.maxWidth, super.maxHeight, required this.keyboardInset})
+    : assert(keyboardInset >= 0);
+
+  // The distance between the bottom of the sheet's content, which avoids the
+  // keyboard, and the bottom edge of the sheet's Material, which extends
+  // behind it. Zero when the keyboard is closed or when
+  // Scaffold.resizeToAvoidBottomInset is false.
+  final double keyboardInset;
+
+  @override
+  bool operator ==(Object other) {
+    if (super != other) {
+      return false;
+    }
+    return other is _BottomSheetBoxConstraints && other.keyboardInset == keyboardInset;
+  }
+
+  @override
+  int get hashCode => Object.hash(super.hashCode, keyboardInset);
+}
+
+// Provides _BottomSheetBoxConstraints.keyboardInset to the _StandardBottomSheets
+// in the Scaffold's bottom sheet slot, which are built before layout.
+class _BottomSheetKeyboardInset extends InheritedWidget {
+  const _BottomSheetKeyboardInset({required this.inset, required super.child});
+
+  final double inset;
+
+  static double of(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<_BottomSheetKeyboardInset>()?.inset ?? 0.0;
+  }
+
+  @override
+  bool updateShouldNotify(_BottomSheetKeyboardInset oldWidget) => inset != oldWidget.inset;
+}
+
 // Used when Scaffold.extendBody is true to wrap the scaffold's body in a MediaQuery
 // whose padding accounts for the height of the bottomNavigationBar and/or the
 // persistentFooterButtons.
@@ -1135,6 +1175,15 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
       bottom - math.max(minInsets.bottom, bottomWidgetsHeight),
     );
 
+    // When the keyboard lifts the bottom sheet's content above it, the sheet's
+    // Material keeps extending down to the edge otherwise available to the
+    // sheet (above any bottom bars), so that a translucent keyboard shows the
+    // sheet's color rather than the Scaffold's background.
+    final double bottomSheetKeyboardInset = math.max(
+      0.0,
+      bottom - bottomWidgetsHeight - contentBottom,
+    );
+
     if (hasChild(_ScaffoldSlot.body)) {
       double bodyMaxHeight = math.max(0.0, contentBottom - contentTop);
 
@@ -1189,14 +1238,23 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     }
 
     if (hasChild(_ScaffoldSlot.bottomSheet)) {
-      final bottomSheetConstraints = BoxConstraints(
+      final double bottomSheetBottom = contentBottom + bottomSheetKeyboardInset;
+      final bottomSheetConstraints = _BottomSheetBoxConstraints(
         maxWidth: fullWidthConstraints.maxWidth,
-        maxHeight: math.max(0.0, contentBottom - contentTop),
+        maxHeight: math.max(0.0, bottomSheetBottom - contentTop),
+        keyboardInset: bottomSheetKeyboardInset,
       );
-      bottomSheetSize = layoutChild(_ScaffoldSlot.bottomSheet, bottomSheetConstraints);
+      final Size sheetSize = layoutChild(_ScaffoldSlot.bottomSheet, bottomSheetConstraints);
       positionChild(
         _ScaffoldSlot.bottomSheet,
-        Offset((size.width - bottomSheetSize.width) / 2.0, contentBottom - bottomSheetSize.height),
+        Offset((size.width - sheetSize.width) / 2.0, bottomSheetBottom - sheetSize.height),
+      );
+      // The floating action button is positioned relative to the sheet's
+      // content, which ends at contentBottom, not to the Material behind the
+      // keyboard.
+      bottomSheetSize = Size(
+        sheetSize.width,
+        math.max(0.0, sheetSize.height - bottomSheetKeyboardInset),
       );
     }
 
@@ -1997,6 +2055,13 @@ class Scaffold extends StatefulWidget {
   /// [showBottomSheet] and [showModalBottomSheet]. Typically it's a widget
   /// that includes [Material].
   ///
+  /// When [resizeToAvoidBottomInset] is true and the software keyboard is
+  /// shown, the sheet's content is kept above the keyboard while the sheet's
+  /// [Material] continues behind it, so that a translucent keyboard shows the
+  /// sheet's surface rather than the scaffold's [backgroundColor]. That surface
+  /// is configured with [BottomSheetThemeData]; decorations painted by the
+  /// [bottomSheet] widget itself do not extend behind the keyboard.
+  ///
   /// See also:
   ///
   ///  * [showBottomSheet], which displays a bottom sheet as a route that can
@@ -2735,6 +2800,12 @@ class ScaffoldState extends State<Scaffold>
   ///
   /// </callout-box>
   ///
+  /// When [Scaffold.resizeToAvoidBottomInset] is true and the software keyboard
+  /// is shown, the sheet's content is kept above the keyboard while the sheet's
+  /// [Material] continues behind it, so that a translucent keyboard shows the
+  /// sheet's surface rather than the scaffold's background. Use
+  /// [backgroundColor] or [BottomSheetThemeData] to configure that surface.
+  ///
   /// See also:
   ///
   ///  * [BottomSheet], which becomes the parent of the widget returned by the
@@ -3164,9 +3235,16 @@ class ScaffoldState extends State<Scaffold>
     double? snackBarWidth;
 
     if (_currentBottomSheet != null || _dismissedBottomSheets.isNotEmpty) {
-      final Widget stack = Stack(
-        alignment: Alignment.bottomCenter,
-        children: <Widget>[..._dismissedBottomSheets, ?_currentBottomSheet?._widget],
+      final Widget stack = LayoutBuilder(
+        builder: (BuildContext context, BoxConstraints constraints) {
+          return _BottomSheetKeyboardInset(
+            inset: (constraints as _BottomSheetBoxConstraints).keyboardInset,
+            child: Stack(
+              alignment: Alignment.bottomCenter,
+              children: <Widget>[..._dismissedBottomSheets, ?_currentBottomSheet?._widget],
+            ),
+          );
+        },
       );
       _addIfNonNull(
         children,
@@ -3505,6 +3583,14 @@ class _StandardBottomSheetState extends State<_StandardBottomSheet> {
 
   @override
   Widget build(BuildContext context) {
+    // Non-zero only while the keyboard lifts this sheet, see _ScaffoldLayout.
+    final double keyboardInset = _BottomSheetKeyboardInset.of(context);
+    // The constraints describe the content, so they grow by the part of the
+    // Material that extends behind the keyboard. This mirrors BottomSheet's own
+    // lookup; its defaults, used when both are null, don't limit the height.
+    final BoxConstraints? constraints =
+        widget.constraints ?? Theme.of(context).bottomSheetTheme.constraints;
+
     return AnimatedBuilder(
       animation: widget.animationController,
       builder: (BuildContext context, Widget? child) {
@@ -3526,12 +3612,20 @@ class _StandardBottomSheetState extends State<_StandardBottomSheet> {
             onDragStart: _handleDragStart,
             onDragEnd: _handleDragEnd,
             onClosing: widget.onClosing!,
-            builder: widget.builder,
+            // Extends the Material behind the keyboard. Always present, so the
+            // content keeps its state when the keyboard shows or hides.
+            builder: (BuildContext context) => Padding(
+              padding: EdgeInsets.only(bottom: keyboardInset),
+              child: widget.builder(context),
+            ),
             backgroundColor: widget.backgroundColor,
             elevation: widget.elevation,
             shape: widget.shape,
             clipBehavior: widget.clipBehavior,
-            constraints: widget.constraints,
+            constraints: constraints?.copyWith(
+              minHeight: constraints.minHeight + keyboardInset,
+              maxHeight: constraints.maxHeight + keyboardInset,
+            ),
           ),
         ),
       ),

packages/material_ui/pending_changelogs/change_2026_10_13_persistent_bottom_sheet_keyboard.yaml

@@ -0,0 +1,3 @@
+changelog: |
+  - Extends the `Material` of a `Scaffold` persistent bottom sheet behind the software keyboard when `resizeToAvoidBottomInset` is true, so that a translucent keyboard shows the sheet's surface instead of the scaffold's background color.
+version: patch