fix_some_padding (#20967)

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

@@ -47,23 +47,37 @@ class ButtonBar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final ButtonThemeData buttonTheme = ButtonTheme.of(context);
     // We divide by 4.0 because we want half of the average of the left and right padding.
-    final double paddingUnit = ButtonTheme.of(context).padding.horizontal / 4.0;
-    return Padding(
-      padding: EdgeInsets.symmetric(
-        vertical: 2.0 * paddingUnit,
-        horizontal: paddingUnit
-      ),
-      child: Row(
-        mainAxisAlignment: alignment,
-        mainAxisSize: mainAxisSize,
-        children: children.map<Widget>((Widget child) {
-          return Padding(
-            padding: EdgeInsets.symmetric(horizontal: paddingUnit),
-            child: child
-          );
-        }).toList()
-      )
+    final double paddingUnit = buttonTheme.padding.horizontal / 4.0;
+    final Widget child = Row(
+      mainAxisAlignment: alignment,
+      mainAxisSize: mainAxisSize,
+      children: children.map<Widget>((Widget child) {
+        return Padding(
+          padding: EdgeInsets.symmetric(horizontal: paddingUnit),
+          child: child
+        );
+      }).toList()
     );
+    switch (buttonTheme.layoutBehavior) {
+      case ButtonBarLayoutBehavior.padded:
+        return Padding(
+          padding: EdgeInsets.symmetric(
+            vertical: 2.0 * paddingUnit,
+            horizontal: paddingUnit
+          ),
+          child: child,
+        );
+      case ButtonBarLayoutBehavior.constrained:
+        return Container(
+          padding: EdgeInsets.symmetric(horizontal: paddingUnit),
+          constraints: const BoxConstraints(minHeight: 52.0),
+          alignment: Alignment.center,
+          child: child,
+        );
+    }
+    assert(false);
+    return null;
   }
 }

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

@@ -26,6 +26,19 @@ enum ButtonTextTheme {
   primary,
 }
 
+/// Used with [ButtonTheme] and [ButtonThemeData] to define how the button bar
+/// should size itself with either constraints or internal padding.
+enum ButtonBarLayoutBehavior {
+  /// Button bars will be constrained to a minimum height of 52.
+  ///
+  /// This setting is require to create button bars which conform to the
+  /// material specification.
+  constrained,
+
+  /// Button bars will calculate their padding from the button theme padding.
+  padded,
+}
+
 /// Used with [ButtonThemeData] to configure the color and geometry of buttons.
 ///
 /// A button theme can be specified as part of the overall Material theme
@@ -60,6 +73,7 @@ class ButtonTheme extends InheritedWidget {
   ButtonTheme({
     Key key,
     ButtonTextTheme textTheme = ButtonTextTheme.normal,
+    ButtonBarLayoutBehavior layoutBehavior = ButtonBarLayoutBehavior.padded,
     double minWidth = 88.0,
     double height = 36.0,
     EdgeInsetsGeometry padding,
@@ -70,13 +84,15 @@ class ButtonTheme extends InheritedWidget {
        assert(minWidth != null && minWidth >= 0.0),
        assert(height != null && height >= 0.0),
        assert(alignedDropdown != null),
+       assert(layoutBehavior != null),
        data = ButtonThemeData(
          textTheme: textTheme,
          minWidth: minWidth,
          height: height,
          padding: padding,
          shape: shape,
-         alignedDropdown: alignedDropdown
+         alignedDropdown: alignedDropdown,
+         layoutBehavior: layoutBehavior,
        ),
        super(key: key, child: child);
 
@@ -113,6 +129,7 @@ class ButtonTheme extends InheritedWidget {
     ShapeBorder shape,
     bool alignedDropdown = false,
     Widget child,
+    ButtonBarLayoutBehavior layoutBehavior = ButtonBarLayoutBehavior.padded,
   }) : assert(textTheme != null),
        assert(minWidth != null && minWidth >= 0.0),
        assert(height != null && height >= 0.0),
@@ -124,6 +141,7 @@ class ButtonTheme extends InheritedWidget {
          padding: padding,
          shape: shape,
          alignedDropdown: alignedDropdown,
+         layoutBehavior: layoutBehavior,
        ),
        super(key: key, child: child);
 
@@ -162,11 +180,13 @@ class ButtonThemeData extends Diagnosticable {
     this.height = 36.0,
     EdgeInsetsGeometry padding,
     ShapeBorder shape,
+    this.layoutBehavior = ButtonBarLayoutBehavior.padded,
     this.alignedDropdown = false,
   }) : assert(textTheme != null),
        assert(minWidth != null && minWidth >= 0.0),
        assert(height != null && height >= 0.0),
        assert(alignedDropdown != null),
+       assert(layoutBehavior != null),
        _padding = padding,
        _shape = shape;
 
@@ -187,6 +207,12 @@ class ButtonThemeData extends Diagnosticable {
   /// size, internal padding, and shape.
   final ButtonTextTheme textTheme;
 
+  /// Defines whether a button bar should size itself with a minimum size
+  /// constraint or padding.
+  ///
+  /// Defaults to [ButtonBarLayoutBehavior.padded].
+  final ButtonBarLayoutBehavior layoutBehavior;
+
   /// Simply a convenience that returns [minWidth] and [height] as a
   /// [BoxConstraints] object:
   /// ```dart

packages/flutter/test/material/button_bar_test.dart

@@ -14,4 +14,54 @@ void main() {
       ),
     );
   });
+
+  testWidgets('ButtonBar has a min height of 52 when using ButtonBarLayoutBehavior.constrained', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      SingleChildScrollView(
+        child: ListBody(
+          children: <Widget>[
+            ButtonTheme.bar(
+              layoutBehavior: ButtonBarLayoutBehavior.constrained,
+              child: const Directionality(
+                textDirection: TextDirection.ltr,
+                child: ButtonBar(
+                  children: <Widget>[
+                    SizedBox(width: 10.0, height: 10.0),
+                  ],
+                ),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final Finder buttonBar = find.byType(ButtonBar);
+    expect(tester.getBottomRight(buttonBar).dy - tester.getTopRight(buttonBar).dy, 52.0);
+  });
+
+  testWidgets('ButtonBar has padding applied when using ButtonBarLayoutBehavior.padded', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      SingleChildScrollView(
+        child: ListBody(
+          children: <Widget>[
+            ButtonTheme.bar(
+              layoutBehavior: ButtonBarLayoutBehavior.padded,
+              child: const Directionality(
+                textDirection: TextDirection.ltr,
+                child: ButtonBar(
+                  children: <Widget>[
+                    SizedBox(width: 10.0, height: 10.0),
+                  ],
+                ),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final Finder buttonBar = find.byType(ButtonBar);
+    expect(tester.getBottomRight(buttonBar).dy - tester.getTopRight(buttonBar).dy, 26.0);
+  });
 }

packages/flutter/test/material/button_theme_test.dart

@@ -15,6 +15,7 @@ void main() {
       borderRadius: BorderRadius.all(Radius.circular(2.0)),
     ));
     expect(theme.alignedDropdown, false);
+    expect(theme.layoutBehavior, ButtonBarLayoutBehavior.padded);
   });
 
   test('ButtonThemeData default overrides', () {