Deprecate Scaffold resizeToAvoidBottomPadding, now resizeToAvoidBottomInset (#26259)

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

@@ -25,6 +25,13 @@ import 'material.dart';
 import 'snack_bar.dart';
 import 'theme.dart';
 
+// Examples can assume:
+// TabController tabController
+// void setState(VoidCallback fn) { }
+// String appBarTitle
+// int tabCount
+// TickerProvider tickerProvider
+
 const FloatingActionButtonLocation _kDefaultFloatingActionButtonLocation = FloatingActionButtonLocation.endFloat;
 const FloatingActionButtonAnimator _kDefaultFloatingActionButtonAnimator = FloatingActionButtonAnimator.scaling;
 
@@ -110,14 +117,14 @@ class ScaffoldPrelayoutGeometry {
   /// and is useful for insetting the [FloatingActionButton] to avoid features like
   /// the system status bar or the keyboard.
   ///
-  /// If [Scaffold.resizeToAvoidBottomPadding] is set to false, [minInsets.bottom]
-  /// will be 0.0 instead of [MediaQuery.padding.bottom].
+  /// If [Scaffold.resizeToAvoidBottomInset] is set to false, [minInsets.bottom]
+  /// will be 0.0.
   final EdgeInsets minInsets;
 
   /// The [Size] of the whole [Scaffold].
   ///
   /// If the [Size] of the [Scaffold]'s contents is modified by values such as
-  /// [Scaffold.resizeToAvoidBottomPadding] or the keyboard opening, then the
+  /// [Scaffold.resizeToAvoidBottomInset] or the keyboard opening, then the
   /// [scaffoldSize] will not reflect those changes.
   ///
   /// This means that [FloatingActionButtonLocation]s designed to reposition
@@ -278,7 +285,10 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     @required this.currentFloatingActionButtonLocation,
     @required this.floatingActionButtonMoveAnimationProgress,
     @required this.floatingActionButtonMotionAnimator,
-  }) : assert(previousFloatingActionButtonLocation != null),
+  }) : assert(minInsets != null),
+       assert(textDirection != null),
+       assert(geometryNotifier != null),
+       assert(previousFloatingActionButtonLocation != null),
        assert(currentFloatingActionButtonLocation != null);
 
   final EdgeInsets minInsets;
@@ -694,6 +704,58 @@ class _FloatingActionButtonTransitionState extends State<_FloatingActionButtonTr
 /// ```
 /// {@end-tool}
 ///
+/// ## Scaffold layout, the keyboard, and display "notches"
+///
+/// The scaffold will expand to fill the available space. That usually
+/// means that it will occupy its entire window or device screen. When
+/// the device's keyboard appears the Scaffold's ancestor [MediaQuery]
+/// widget's [MediaQueryData.viewInsets] changes and the Scaffold will
+/// be rebuilt. By default the scaffold's [body] is resized to make
+/// room for the keyboard. To prevent the resize set
+/// [resizeToAvoidBottomInset] to false. In either case the focused
+/// widget will be scrolled into view if it's within a scrollable
+/// container.
+///
+/// The [MediaQueryData.padding] value defines areas that might
+/// not be completely visible, like the display "notch" on the iPhone
+/// X. The scaffold's [body] is not inset by this padding value
+/// although an [appBar] or [bottomNavigationBar] will typically
+/// cause the body to avoid the padding. The [SafeArea]
+/// widget can be used within the scaffold's body to avoid areas
+/// like display notches.
+///
+/// ## Troubleshooting
+///
+/// ### Nested Scaffolds
+///
+/// The Scaffold was designed to be the single top level container for
+/// a [MaterialApp] and it's typically not necessary to nest
+/// scaffolds. For example in a tabbed UI, where the
+/// [bottomNavigationBar] is a [TabBar] and the body is a
+/// [TabBarView], you might be tempted to make each tab bar view a
+/// scaffold with a differently titled AppBar. It would be better to add a
+/// listener to the [TabController] that updates the AppBar.
+///
+/// ## Sample Code
+///
+/// Add a listener to the app's tab controller so that the [AppBar] title of the
+/// app's one and only scaffold is reset each time a new tab is selected.
+///
+/// ```dart
+/// tabController = TabController(vsync: tickerProvider, length: tabCount)..addListener(() {
+///   if (!tabController.indexIsChanging) {
+///     setState(() {
+///       // Rebuild the enclosing scaffold with a new AppBar title
+///       appBarTitle = 'Tab ${tabController.index}';
+///     });
+///   }
+/// });
+/// ```
+///
+/// Although there are some use cases, like a presentation app that
+/// shows embedded flutter content, where nested scaffolds are
+/// appropriate, it's best to avoid nesting scaffolds.
+///
 /// See also:
 ///
 ///  * [AppBar], which is a horizontal bar typically shown at the top of an app
@@ -731,7 +793,8 @@ class Scaffold extends StatefulWidget {
     this.bottomNavigationBar,
     this.bottomSheet,
     this.backgroundColor,
-    this.resizeToAvoidBottomPadding = true,
+    this.resizeToAvoidBottomPadding,
+    this.resizeToAvoidBottomInset,
     this.primary = true,
     this.drawerDragStartBehavior = DragStartBehavior.start,
   }) : assert(primary != null),
@@ -743,9 +806,11 @@ class Scaffold extends StatefulWidget {
 
   /// The primary content of the scaffold.
   ///
-  /// Displayed below the app bar and behind the [floatingActionButton] and
-  /// [drawer]. To avoid the body being resized to avoid the window padding
-  /// (e.g., from the onscreen keyboard), see [resizeToAvoidBottomPadding].
+  /// Displayed below the [appBar], above the bottom of the ambient
+  /// [MediaQuery]'s [MediaQueryData.viewInsets], and behind the
+  /// [floatingActionButton] and [drawer]. If [resizeToAvoidBottomInset] is
+  /// false then the body is not resized when the onscreen keyboard appears,
+  /// i.e. it is not inset by `viewInsets.bottom`.
   ///
   /// The widget in the body of the scaffold is positioned at the top-left of
   /// the available space between the app bar and the bottom of the scaffold. To
@@ -850,15 +915,25 @@ class Scaffold extends StatefulWidget {
   ///  * [showModalBottomSheet], which displays a modal bottom sheet.
   final Widget bottomSheet;
 
-  /// Whether the [body] (and other floating widgets) should size themselves to
-  /// avoid the window's bottom padding.
+  /// This flag is deprecated, please use [resizeToAvoidBottomInset]
+  /// instead.
+  ///
+  /// Originally the name referred [MediaQueryData.padding]. Now it refers
+  /// [MediaQueryData.viewInsets], so using [resizeToAvoidBottomInset]
+  /// should be clearer to readers.
+  @Deprecated('Use resizeToAvoidBottomInset to specify if the body should resize when the keyboard appears')
+  final bool resizeToAvoidBottomPadding;
+
+  /// If true the [body] and the scaffold's floating widgets should size
+  /// themselves to avoid the onscreen keyboard whose height is defined by the
+  /// ambient [MediaQuery]'s [MediaQueryData.viewInsets] `bottom` property.
   ///
   /// For example, if there is an onscreen keyboard displayed above the
   /// scaffold, the body can be resized to avoid overlapping the keyboard, which
   /// prevents widgets inside the body from being obscured by the keyboard.
   ///
   /// Defaults to true.
-  final bool resizeToAvoidBottomPadding;
+  final bool resizeToAvoidBottomInset;
 
   /// Whether this scaffold is being displayed at the top of the screen.
   ///
@@ -1399,6 +1474,12 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
 
   _ScaffoldGeometryNotifier _geometryNotifier;
 
+  // Backwards compatibility for deprecated resizeToAvoidBottomPadding property
+  bool get _resizeToAvoidBottomInset {
+    // ignore: deprecated_member_use
+    return widget.resizeToAvoidBottomInset ?? widget.resizeToAvoidBottomPadding ?? true;
+  }
+
   @override
   void initState() {
     super.initState();
@@ -1479,19 +1560,22 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     @required bool removeTopPadding,
     @required bool removeRightPadding,
     @required bool removeBottomPadding,
+    bool removeBottomInset = false,
   }) {
+    MediaQueryData data = MediaQuery.of(context).removePadding(
+      removeLeft: removeLeftPadding,
+      removeTop: removeTopPadding,
+      removeRight: removeRightPadding,
+      removeBottom: removeBottomPadding,
+    );
+    if (removeBottomInset)
+      data = data.removeViewInsets(removeBottom: true);
+
     if (child != null) {
       children.add(
         LayoutId(
           id: childId,
-          child: MediaQuery.removePadding(
-            context: context,
-            removeLeft: removeLeftPadding,
-            removeTop: removeTopPadding,
-            removeRight: removeRightPadding,
-            removeBottom: removeBottomPadding,
-            child: child,
-          ),
+          child: MediaQuery(data: data, child: child),
         ),
       );
     }
@@ -1580,8 +1664,8 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
       removeLeftPadding: false,
       removeTopPadding: widget.appBar != null,
       removeRightPadding: false,
-      removeBottomPadding: widget.bottomNavigationBar != null ||
-        widget.persistentFooterButtons != null,
+      removeBottomPadding: widget.bottomNavigationBar != null || widget.persistentFooterButtons != null,
+      removeBottomInset: _resizeToAvoidBottomInset,
     );
 
     if (widget.appBar != null) {
@@ -1606,8 +1690,6 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     }
 
     if (_snackBars.isNotEmpty) {
-      final bool removeBottomPadding = widget.persistentFooterButtons != null ||
-        widget.bottomNavigationBar != null;
       _addIfNonNull(
         children,
         _snackBars.first._widget,
@@ -1615,7 +1697,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
         removeLeftPadding: false,
         removeTopPadding: true,
         removeRightPadding: false,
-        removeBottomPadding: removeBottomPadding,
+        removeBottomPadding: widget.bottomNavigationBar != null || widget.persistentFooterButtons != null,
       );
     }
 
@@ -1676,7 +1758,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
         removeLeftPadding: false,
         removeTopPadding: true,
         removeRightPadding: false,
-        removeBottomPadding: widget.resizeToAvoidBottomPadding,
+        removeBottomPadding: _resizeToAvoidBottomInset,
       );
     }
 
@@ -1722,7 +1804,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
 
     // The minimum insets for contents of the Scaffold to keep visible.
     final EdgeInsets minInsets = mediaQuery.padding.copyWith(
-      bottom: widget.resizeToAvoidBottomPadding ? mediaQuery.viewInsets.bottom : 0.0,
+      bottom: _resizeToAvoidBottomInset ? mediaQuery.viewInsets.bottom : 0.0,
     );
 
     return _ScaffoldScope(

packages/flutter/lib/src/widgets/media_query.dart

@@ -30,6 +30,25 @@ enum Orientation {
 /// If no [MediaQuery] is in scope then the [MediaQuery.of] method will throw an
 /// exception, unless the `nullOk` argument is set to true, in which case it
 /// returns null.
+///
+/// MediaQueryData includes two [EdgeInsets] values:
+/// [padding] and [viewInsets]. These
+/// values reflect the configuration of the device and are used by
+/// many top level widgets, like [SafeArea] and the Cupertino and
+/// Material scaffold widgets. The padding value defines areas that
+/// might not be completely visible, like the display "notch" on the
+/// iPhone X. The viewInsets value defines areas that aren't visible at
+/// all, typically because they're obscured by the device's keyboard.
+///
+/// The viewInsets and padding values are independent, they're both
+/// measured from the edges of the MediaQuery widget's bounds. The
+/// bounds of the top level MediaQuery created by [WidgetsApp] are the
+/// same as the window that contains the app.
+///
+/// Widgets whose layouts consume space defined by [viewInsets] or
+/// [padding] shoud enclose their children in secondary MediaQuery
+/// widgets that reduce those properties by the same amount.
+/// The [removePadding] and [removeInsets] methods are useful for this.
 @immutable
 class MediaQueryData {
   /// Creates data for a media query with explicit values.
@@ -67,7 +86,7 @@ class MediaQueryData {
       boldText = window.accessibilityFeatures.boldText,
       alwaysUse24HourFormat = window.alwaysUse24HourFormat;
 
-  /// The size of the media in logical pixel (e.g, the size of the screen).
+  /// The size of the media in logical pixels (e.g, the size of the screen).
   ///
   /// Logical pixels are roughly the same visual size across devices. Physical
   /// pixels are the size of the actual hardware pixels on the device. The
@@ -91,17 +110,25 @@ class MediaQueryData {
   ///    textScaleFactor defined for a [BuildContext].
   final double textScaleFactor;
 
-  /// The number of physical pixels on each side of the display rectangle into
-  /// which the application can render, but over which the operating system
-  /// will likely place system UI, such as the keyboard, that fully obscures
-  /// any content.
+  /// The parts of the display that are completely obscured by system UI,
+  /// typically by the device's keyboard.
+  ///
+  /// When a mobile device's keyboard is visible `viewInsets.bottom`
+  /// corresponds to the top of the keyboard.
+  ///
+  /// This value is independent of the [padding]: both values are
+  /// measured from the edges of the [MediaQuery] widget's bounds. The
+  /// bounds of the top level MediaQuery created by [WidgetsApp] are the
+  /// same as the window (often the mobile device screen) that contains the app.
+  ///
+  /// See also:
+  ///
+  /// * [MediaQueryData], which provides some additional detail about this
+  ///   property and how it differs from [padding].
   final EdgeInsets viewInsets;
 
-  /// The number of physical pixels on each side of the display rectangle into
-  /// which the application can render, but which may be partially obscured by
-  /// system UI (such as the system notification area), or or physical
-  /// intrusions in the display (e.g. overscan regions on television screens or
-  /// phone sensor housings).
+  /// The parts of the display that are partially obscured by system UI,
+  /// typically by the hardware display "notches" or the system status bar.
   ///
   /// If you consumed this padding (e.g. by building a widget that envelops or
   /// accounts for this padding in its layout in such a way that children are
@@ -111,6 +138,8 @@ class MediaQueryData {
   ///
   /// See also:
   ///
+  ///  * [MediaQueryData], which provides some additional detail about this
+  ///    property and how it differs from [viewInsets].
   ///  * [SafeArea], a widget that consumes this padding with a [Padding] widget
   ///    and automatically removes it from the [MediaQuery] for its child.
   final EdgeInsets padding;

packages/flutter/test/material/scaffold_test.dart

@@ -59,7 +59,20 @@ void main() {
       child: Scaffold(
         appBar: AppBar(title: const Text('Title')),
         body: Container(key: bodyKey),
-        resizeToAvoidBottomPadding: false,
+        resizeToAvoidBottomInset: false,
+      ),
+    )));
+
+    bodyBox = tester.renderObject(find.byKey(bodyKey));
+    expect(bodyBox.size, equals(const Size(800.0, 544.0)));
+
+    // Backwards compatiblity: deprecated resizeToAvoidBottomPadding flag
+    await tester.pumpWidget(boilerplate(MediaQuery(
+      data: const MediaQueryData(viewInsets: EdgeInsets.only(bottom: 100.0)),
+      child: Scaffold(
+        appBar: AppBar(title: const Text('Title')),
+        body: Container(key: bodyKey),
+        resizeToAvoidBottomPadding: false, // ignore: deprecated_member_use
       ),
     )));
 
@@ -1200,6 +1213,58 @@ void main() {
       expect(scaffoldState.isDrawerOpen, true);
     });
   });
+
+  testWidgets('Nested scaffold body insets', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/20295
+
+    final Key bodyKey = UniqueKey();
+
+    Widget buildFrame(bool innerResizeToAvoidBottomInset, bool outerResizeToAvoidBottomInset) {
+      return Directionality(
+        textDirection: TextDirection.ltr,
+        child: MediaQuery(
+          data: const MediaQueryData(viewInsets: EdgeInsets.only(bottom: 100.0)),
+          child: Builder(
+            builder: (BuildContext context) {
+              return Scaffold(
+                resizeToAvoidBottomInset: outerResizeToAvoidBottomInset,
+                body: Builder(
+                  builder: (BuildContext context) {
+                    return Scaffold(
+                      resizeToAvoidBottomInset: innerResizeToAvoidBottomInset,
+                      body: Container(key: bodyKey),
+                    );
+                  },
+                ),
+              );
+            },
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(true, true));
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 500.0));
+
+    await tester.pumpWidget(buildFrame(false, true));
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 500.0));
+
+    await tester.pumpWidget(buildFrame(true, false));
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 500.0));
+
+    // This is the only case where the body is not bottom inset.
+    await tester.pumpWidget(buildFrame(false, false));
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 600.0));
+
+    await tester.pumpWidget(buildFrame(null, null));  // resizeToAvoidBottomInset default  is true
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 500.0));
+
+    await tester.pumpWidget(buildFrame(null, false));
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 500.0));
+
+    await tester.pumpWidget(buildFrame(false, null));
+    expect(tester.getSize(find.byKey(bodyKey)), const Size(800.0, 500.0));
+  });
 }
 
 class _GeometryListener extends StatefulWidget {