Ensure FloatingActionButtonLocations are always within safe interactive areas (#60248)

packages/flutter/lib/src/material/floating_action_button_location.dart

@@ -413,14 +413,26 @@ abstract class StandardFabLocation extends FloatingActionButtonLocation {
 
 }
 
-/// Mixin for a "top" floating action button location, such as [FloatingActionButtonLocation.startTop].
+/// Mixin for a "top" floating action button location, such as
+/// [FloatingActionButtonLocation.startTop].
+///
+/// The [adjustment], typically [kMiniButtonOffsetAdjustment], is ignored in the
+/// Y axis of "top" positions. For "top" positions, the X offset is adjusted to
+/// move closer to the edge of the screen. This is so that a minified floating
+/// action button appears to align with [CircleAvatar]s in the
+/// [ListTile.leading] slot of a [ListTile] in a [ListView] in the
+/// [Scaffold.body].
 mixin FabTopOffsetY on StandardFabLocation {
   /// Calculates y-offset for [FloatingActionButtonLocation]s floating over
   /// the transition between the [Scaffold.appBar] and the [Scaffold.body].
   @override
   double getOffsetY(ScaffoldPrelayoutGeometry scaffoldGeometry, double adjustment) {
-    final double fabHalfHeight = scaffoldGeometry.floatingActionButtonSize.height / 2.0;
-    return scaffoldGeometry.contentTop - fabHalfHeight;
+    if (scaffoldGeometry.contentTop > scaffoldGeometry.minViewPadding.top) {
+      final double fabHalfHeight = scaffoldGeometry.floatingActionButtonSize.height / 2.0;
+      return scaffoldGeometry.contentTop - fabHalfHeight;
+    }
+    // Otherwise, ensure we are placed within the bounds of a safe area.
+    return scaffoldGeometry.minViewPadding.top;
   }
 }
 
@@ -434,8 +446,12 @@ mixin FabFloatOffsetY on StandardFabLocation {
     final double bottomSheetHeight = scaffoldGeometry.bottomSheetSize.height;
     final double fabHeight = scaffoldGeometry.floatingActionButtonSize.height;
     final double snackBarHeight = scaffoldGeometry.snackBarSize.height;
+    final double safeMargin = math.max(
+      kFloatingActionButtonMargin,
+      scaffoldGeometry.minViewPadding.bottom,
+    );
 
-    double fabY = contentBottom - fabHeight - kFloatingActionButtonMargin;
+    double fabY = contentBottom - fabHeight - safeMargin;
     if (snackBarHeight > 0.0)
       fabY = math.min(fabY, contentBottom - snackBarHeight - fabHeight - kFloatingActionButtonMargin);
     if (bottomSheetHeight > 0.0)
@@ -453,19 +469,21 @@ mixin FabDockedOffsetY on StandardFabLocation {
   @override
   double getOffsetY(ScaffoldPrelayoutGeometry scaffoldGeometry, double adjustment) {
     final double contentBottom = scaffoldGeometry.contentBottom;
+    final double contentMargin = scaffoldGeometry.scaffoldSize.height - contentBottom;
+    final double bottomViewPadding = scaffoldGeometry.minViewPadding.bottom;
     final double bottomSheetHeight = scaffoldGeometry.bottomSheetSize.height;
     final double fabHeight = scaffoldGeometry.floatingActionButtonSize.height;
     final double snackBarHeight = scaffoldGeometry.snackBarSize.height;
+    final double safeMargin = bottomViewPadding > contentMargin ? bottomViewPadding : 0.0;
 
-    double fabY = contentBottom - fabHeight / 2.0;
+    double fabY = contentBottom - fabHeight / 2.0 - safeMargin;
     // The FAB should sit with a margin between it and the snack bar.
     if (snackBarHeight > 0.0)
       fabY = math.min(fabY, contentBottom - snackBarHeight - fabHeight - kFloatingActionButtonMargin);
     // The FAB should sit with its center in front of the top of the bottom sheet.
     if (bottomSheetHeight > 0.0)
       fabY = math.min(fabY, contentBottom - bottomSheetHeight - fabHeight / 2.0);
-
-    final double maxFabY = scaffoldGeometry.scaffoldSize.height - fabHeight;
+    final double maxFabY = scaffoldGeometry.scaffoldSize.height - fabHeight - safeMargin;
     return math.min(maxFabY, fabY);
   }
 }

packages/flutter/lib/src/material/scaffold.dart

@@ -80,6 +80,7 @@ class ScaffoldPrelayoutGeometry {
     @required this.contentTop,
     @required this.floatingActionButtonSize,
     @required this.minInsets,
+    @required this.minViewPadding,
     @required this.scaffoldSize,
     @required this.snackBarSize,
     @required this.textDirection,
@@ -134,6 +135,16 @@ class ScaffoldPrelayoutGeometry {
   /// will be 0.0.
   final EdgeInsets minInsets;
 
+  /// The minimum padding to inset interactive elements to be within a safe,
+  /// un-obscured space.
+  ///
+  /// This value reflects the [MediaQuery.viewPadding] of the [Scaffold]'s
+  /// [BuildContext] when [Scaffold.resizeToAvoidBottomInset] is false or and
+  /// the [MediaQuery.viewInsets] > 0.0. This helps distinguish between
+  /// different types of obstructions on the screen, such as software keyboards
+  /// and physical device notches.
+  final EdgeInsets minViewPadding;
+
   /// The [Size] of the whole [Scaffold].
   ///
   /// If the [Size] of the [Scaffold]'s contents is modified by values such as
@@ -389,6 +400,7 @@ class _BodyBuilder extends StatelessWidget {
 class _ScaffoldLayout extends MultiChildLayoutDelegate {
   _ScaffoldLayout({
     @required this.minInsets,
+    @required this.minViewPadding,
     @required this.textDirection,
     @required this.geometryNotifier,
     // for floating action button
@@ -410,6 +422,7 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
   final bool extendBody;
   final bool extendBodyBehindAppBar;
   final EdgeInsets minInsets;
+  final EdgeInsets minViewPadding;
   final TextDirection textDirection;
   final _ScaffoldGeometryNotifier geometryNotifier;
 
@@ -536,6 +549,7 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
         scaffoldSize: size,
         snackBarSize: snackBarSize,
         textDirection: textDirection,
+        minViewPadding: minViewPadding,
       );
       final Offset currentFabOffset = currentFloatingActionButtonLocation.getOffset(currentGeometry);
       final Offset previousFabOffset = previousFloatingActionButtonLocation.getOffset(currentGeometry);
@@ -2497,6 +2511,12 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
       bottom: _resizeToAvoidBottomInset ? mediaQuery.viewInsets.bottom : 0.0,
     );
 
+    // The minimum viewPadding for interactive elements positioned by the
+    // Scaffold to keep within safe interactive areas.
+    final EdgeInsets minViewPadding = mediaQuery.viewPadding.copyWith(
+      bottom: _resizeToAvoidBottomInset &&  mediaQuery.viewInsets.bottom != 0.0 ? 0.0 : null,
+    );
+
     // extendBody locked when keyboard is open
     final bool _extendBody = minInsets.bottom <= 0 && widget.extendBody;
 
@@ -2514,6 +2534,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
                 extendBody: _extendBody,
                 extendBodyBehindAppBar: widget.extendBodyBehindAppBar,
                 minInsets: minInsets,
+                minViewPadding: minViewPadding,
                 currentFloatingActionButtonLocation: _floatingActionButtonLocation,
                 floatingActionButtonMoveAnimationProgress: _floatingActionButtonMoveController.value,
                 floatingActionButtonMotionAnimator: _floatingActionButtonAnimator,