Fix bottom app bar height and end-contained fab location (#123746)

Fix bottom app bar height and end-contained fab location

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

@@ -194,9 +194,12 @@ class _BottomAppBarState extends State<BottomAppBar> {
     final Color effectiveColor = isMaterial3 ? color : ElevationOverlay.applyOverlay(context, color, elevation);
     final Color shadowColor = widget.shadowColor ?? babTheme.shadowColor ?? defaults.shadowColor!;
 
-    final Widget child = Padding(
-      padding: widget.padding ?? babTheme.padding ?? (isMaterial3 ? const EdgeInsets.symmetric(vertical: 12.0, horizontal: 16.0) : EdgeInsets.zero),
-      child: widget.child,
+    final Widget child = SizedBox(
+      height: height,
+      child: Padding(
+        padding: widget.padding ?? babTheme.padding ?? (isMaterial3 ? const EdgeInsets.symmetric(vertical: 12.0, horizontal: 16.0) : EdgeInsets.zero),
+        child: widget.child,
+      ),
     );
 
     final Material material = Material(
@@ -209,16 +212,14 @@ class _BottomAppBarState extends State<BottomAppBar> {
       child: SafeArea(child: child),
     );
 
-    final PhysicalShape physicalShape = PhysicalShape(
+    return PhysicalShape(
       clipper: clipper,
       elevation: elevation,
       shadowColor: shadowColor,
       color: effectiveColor,
       clipBehavior: widget.clipBehavior,
       child: material,
-     );
-
-    return SizedBox(height: height, child: physicalShape);
+    );
   }
 }
 

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

@@ -630,20 +630,24 @@ mixin FabContainedOffsetY on StandardFabLocation {
     final double contentMargin = scaffoldGeometry.scaffoldSize.height - contentBottom;
     final double bottomViewPadding = scaffoldGeometry.minViewPadding.bottom;
     final double fabHeight = scaffoldGeometry.floatingActionButtonSize.height;
-    final double bottomMinInset = scaffoldGeometry.minInsets.bottom;
 
-    double safeMargin = 0.0;
-    if (contentMargin > bottomMinInset + fabHeight / 2.0) {
-      // If contentMargin is higher than bottomMinInset enough to display the
+    double safeMargin;
+    if (contentMargin > bottomViewPadding + fabHeight) {
+      // If contentMargin is higher than bottomViewPadding enough to display the
       // FAB without clipping, don't provide a margin
       safeMargin = 0.0;
     } else {
       safeMargin = bottomViewPadding;
     }
 
-    final double fabY = contentBottom - fabHeight / 2.0 - safeMargin;
+    // This is to compute the distance between the content bottom to the top edge
+    // of the floating action button. This can be negative if content margin is
+    // too small.
+    final double contentBottomToFabTop = (contentMargin - bottomViewPadding - fabHeight) / 2.0;
+    final double fabY = contentBottom + contentBottomToFabTop;
     final double maxFabY = scaffoldGeometry.scaffoldSize.height - fabHeight - safeMargin;
-    return math.min(maxFabY, fabY + contentMargin / 2);
+
+    return math.min(maxFabY, fabY);
   }
 }
 

packages/flutter/test/material/bottom_app_bar_test.dart

@@ -616,6 +616,44 @@ void main() {
     physicalShape = tester.widget(find.byType(PhysicalShape).at(0));
     expect(physicalShape.clipper.toString(), 'ShapeBorderClipper');
   });
+
+  testWidgets('BottomAppBar adds bottom padding to height', (WidgetTester tester) async {
+    const double bottomPadding = 35.0;
+
+    await tester.pumpWidget(
+      MediaQuery(
+        data: const MediaQueryData(
+          padding: EdgeInsets.only(bottom: bottomPadding),
+          viewPadding: EdgeInsets.only(bottom: bottomPadding),
+        ),
+        child: MaterialApp(
+          theme: ThemeData(useMaterial3: true),
+          home: Scaffold(
+            floatingActionButtonLocation: FloatingActionButtonLocation.endContained,
+            floatingActionButton: FloatingActionButton(onPressed: () { }),
+            bottomNavigationBar: BottomAppBar(
+              child: IconButton(
+                icon: const Icon(Icons.search),
+                onPressed: () {},
+              ),
+            ),
+          ),
+        ),
+      )
+    );
+
+    final Rect bottomAppBar = tester.getRect(find.byType(BottomAppBar));
+    final Rect iconButton = tester.getRect(find.widgetWithIcon(IconButton, Icons.search));
+    final Rect fab = tester.getRect(find.byType(FloatingActionButton));
+
+    // The height of the bottom app bar should be its height(default is 80.0) + bottom safe area height.
+    expect(bottomAppBar.height, 80.0 + bottomPadding);
+
+    // The vertical position of the icon button and fab should be center of the area excluding the bottom padding.
+    final double barCenter = bottomAppBar.topLeft.dy + (bottomAppBar.height - bottomPadding) / 2;
+    expect(iconButton.center.dy, barCenter);
+    expect(fab.center.dy, barCenter);
+  });
 }
 
 // The bottom app bar clip path computation is only available at paint time.