Added ButtonStyle.alignment property (#73894)

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

@@ -114,6 +114,7 @@ class ButtonStyle with Diagnosticable {
     this.tapTargetSize,
     this.animationDuration,
     this.enableFeedback,
+    this.alignment,
   });
 
   /// The style for a button's [Text] widget descendants.
@@ -208,6 +209,16 @@ class ButtonStyle with Diagnosticable {
   ///  * [Feedback] for providing platform-specific feedback to certain actions.
   final bool? enableFeedback;
 
+  /// The alignment of the button's child.
+  ///
+  /// Typically buttons are sized to be just big enough to contain the child and its
+  /// padding. If the button's size is constrained to a fixed size, for example by
+  /// enclosing it with a [SizedBox], this property defines how the child is aligned
+  /// within the available space.
+  ///
+  /// Always defaults to [Alignment.center].
+  final AlignmentGeometry? alignment;
+
   /// Returns a copy of this ButtonStyle with the given fields replaced with
   /// the new values.
   ButtonStyle copyWith({
@@ -226,6 +237,7 @@ class ButtonStyle with Diagnosticable {
     MaterialTapTargetSize? tapTargetSize,
     Duration? animationDuration,
     bool? enableFeedback,
+    AlignmentGeometry? alignment,
   }) {
     return ButtonStyle(
       textStyle: textStyle ?? this.textStyle,
@@ -243,6 +255,7 @@ class ButtonStyle with Diagnosticable {
       tapTargetSize: tapTargetSize ?? this.tapTargetSize,
       animationDuration: animationDuration ?? this.animationDuration,
       enableFeedback: enableFeedback ?? this.enableFeedback,
+      alignment: alignment ?? this.alignment,
     );
   }
 
@@ -270,6 +283,7 @@ class ButtonStyle with Diagnosticable {
       tapTargetSize: tapTargetSize ?? style.tapTargetSize,
       animationDuration: animationDuration ?? style.animationDuration,
       enableFeedback: enableFeedback ?? style.enableFeedback,
+      alignment: alignment ?? style.alignment,
     );
   }
 
@@ -291,6 +305,7 @@ class ButtonStyle with Diagnosticable {
       tapTargetSize,
       animationDuration,
       enableFeedback,
+      alignment,
     );
   }
 
@@ -315,7 +330,8 @@ class ButtonStyle with Diagnosticable {
         && other.visualDensity == visualDensity
         && other.tapTargetSize == tapTargetSize
         && other.animationDuration == animationDuration
-        && other.enableFeedback == enableFeedback;
+        && other.enableFeedback == enableFeedback
+        && other.alignment == alignment;
   }
 
   @override
@@ -336,6 +352,7 @@ class ButtonStyle with Diagnosticable {
     properties.add(EnumProperty<MaterialTapTargetSize>('tapTargetSize', tapTargetSize, defaultValue: null));
     properties.add(DiagnosticsProperty<Duration>('animationDuration', animationDuration, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('enableFeedback', enableFeedback, defaultValue: null));
+    properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, defaultValue: null));
   }
 
   /// Linearly interpolate between two [ButtonStyle]s.
@@ -359,6 +376,7 @@ class ButtonStyle with Diagnosticable {
       tapTargetSize: t < 0.5 ? a?.tapTargetSize : b?.tapTargetSize,
       animationDuration: t < 0.5 ? a?.animationDuration : b?.animationDuration,
       enableFeedback: t < 0.5 ? a?.enableFeedback : b?.enableFeedback,
+      alignment: AlignmentGeometry.lerp(a?.alignment, b?.alignment, t),
     );
   }
 

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

@@ -283,6 +283,7 @@ class _ButtonStyleState extends State<ButtonStyleButton> with TickerProviderStat
     final MaterialTapTargetSize? resolvedTapTargetSize = effectiveValue((ButtonStyle? style) => style?.tapTargetSize);
     final Duration? resolvedAnimationDuration = effectiveValue((ButtonStyle? style) => style?.animationDuration);
     final bool? resolvedEnableFeedback = effectiveValue((ButtonStyle? style) => style?.enableFeedback);
+    final AlignmentGeometry? resolvedAlignment = effectiveValue((ButtonStyle? style) => style?.alignment);
     final Offset densityAdjustment = resolvedVisualDensity!.baseSizeAdjustment;
     final BoxConstraints effectiveConstraints = resolvedVisualDensity.effectiveConstraints(
       BoxConstraints(
@@ -360,7 +361,8 @@ class _ButtonStyleState extends State<ButtonStyleButton> with TickerProviderStat
             data: IconThemeData(color: resolvedForegroundColor),
             child: Padding(
               padding: padding,
-              child: Center(
+              child: Align(
+                alignment: resolvedAlignment!,
                 widthFactor: 1.0,
                 heightFactor: 1.0,
                 child: widget.child,

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

@@ -147,6 +147,7 @@ class ElevatedButton extends ButtonStyleButton {
     MaterialTapTargetSize? tapTargetSize,
     Duration? animationDuration,
     bool? enableFeedback,
+    AlignmentGeometry? alignment,
   }) {
     final MaterialStateProperty<Color?>? backgroundColor = (onSurface == null && primary == null)
       ? null
@@ -180,6 +181,7 @@ class ElevatedButton extends ButtonStyleButton {
       tapTargetSize: tapTargetSize,
       animationDuration: animationDuration,
       enableFeedback: enableFeedback,
+      alignment: alignment,
     );
   }
 
@@ -238,6 +240,7 @@ class ElevatedButton extends ButtonStyleButton {
   /// * `tapTargetSize` - theme.materialTapTargetSize
   /// * `animationDuration` - kThemeChangeDuration
   /// * `enableFeedback` - true
+  /// * `alignment` - Alignment.center
   ///
   /// The default padding values for the [ElevatedButton.icon] factory are slightly different:
   ///
@@ -280,6 +283,7 @@ class ElevatedButton extends ButtonStyleButton {
       tapTargetSize: theme.materialTapTargetSize,
       animationDuration: kThemeChangeDuration,
       enableFeedback: true,
+      alignment: Alignment.center,
     );
   }
 

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

@@ -139,6 +139,7 @@ class OutlinedButton extends ButtonStyleButton {
     MaterialTapTargetSize? tapTargetSize,
     Duration? animationDuration,
     bool? enableFeedback,
+    AlignmentGeometry? alignment,
   }) {
     final MaterialStateProperty<Color?>? foregroundColor = (onSurface == null && primary == null)
       ? null
@@ -166,6 +167,7 @@ class OutlinedButton extends ButtonStyleButton {
       tapTargetSize: tapTargetSize,
       animationDuration: animationDuration,
       enableFeedback: enableFeedback,
+      alignment: alignment,
     );
   }
 
@@ -217,6 +219,7 @@ class OutlinedButton extends ButtonStyleButton {
   /// * `tapTargetSize` - theme.materialTapTargetSize
   /// * `animationDuration` - kThemeChangeDuration
   /// * `enableFeedback` - true
+  /// * `alignment` - Alignment.center
   @override
   ButtonStyle defaultStyleOf(BuildContext context) {
     final ThemeData theme = Theme.of(context);
@@ -249,6 +252,7 @@ class OutlinedButton extends ButtonStyleButton {
       tapTargetSize: theme.materialTapTargetSize,
       animationDuration: kThemeChangeDuration,
       enableFeedback: true,
+      alignment: Alignment.center,
     );
   }
 

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

@@ -145,6 +145,7 @@ class TextButton extends ButtonStyleButton {
     MaterialTapTargetSize? tapTargetSize,
     Duration? animationDuration,
     bool? enableFeedback,
+    AlignmentGeometry? alignment,
   }) {
     final MaterialStateProperty<Color?>? foregroundColor = (onSurface == null && primary == null)
       ? null
@@ -172,6 +173,7 @@ class TextButton extends ButtonStyleButton {
       tapTargetSize: tapTargetSize,
       animationDuration: animationDuration,
       enableFeedback: enableFeedback,
+      alignment: alignment,
     );
   }
 
@@ -226,6 +228,7 @@ class TextButton extends ButtonStyleButton {
   /// * `tapTargetSize` - theme.materialTapTargetSize
   /// * `animationDuration` - kThemeChangeDuration
   /// * `enableFeedback` - true
+  /// * `alignment` - Alignment.center
   ///
   /// The default padding values for the [TextButton.icon] factory are slightly different:
   ///
@@ -267,6 +270,7 @@ class TextButton extends ButtonStyleButton {
       tapTargetSize: theme.materialTapTargetSize,
       animationDuration: kThemeChangeDuration,
       enableFeedback: true,
+      alignment: Alignment.center,
     );
   }
 

packages/flutter/test/material/elevated_button_test.dart

@@ -48,6 +48,9 @@ void main() {
     expect(material.textStyle!.fontWeight, FontWeight.w500);
     expect(material.type, MaterialType.button);
 
+    final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+    expect(align.alignment, Alignment.center);
+
     final Offset center = tester.getCenter(find.byType(ElevatedButton));
     final TestGesture gesture = await tester.startGesture(center);
     await tester.pump(); // start the splash animation

packages/flutter/test/material/elevated_button_theme_test.dart

@@ -39,6 +39,9 @@ void main() {
     expect(material.textStyle!.fontFamily, 'Roboto');
     expect(material.textStyle!.fontSize, 14);
     expect(material.textStyle!.fontWeight, FontWeight.w500);
+
+    final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+    expect(align.alignment, Alignment.center);
   });
 
   group('[Theme, TextTheme, ElevatedButton style overrides]', () {
@@ -57,6 +60,7 @@ void main() {
     const MaterialTapTargetSize tapTargetSize = MaterialTapTargetSize.shrinkWrap;
     const Duration animationDuration = Duration(milliseconds: 25);
     const bool enableFeedback = false;
+    const AlignmentGeometry alignment = Alignment.centerLeft;
 
     final ButtonStyle style = ElevatedButton.styleFrom(
       primary: primaryColor,
@@ -74,6 +78,7 @@ void main() {
       tapTargetSize: tapTargetSize,
       animationDuration: animationDuration,
       enableFeedback: enableFeedback,
+      alignment: alignment,
     );
 
     Widget buildFrame({ ButtonStyle? buttonStyle, ButtonStyle? themeStyle, ButtonStyle? overallStyle }) {
@@ -137,6 +142,8 @@ void main() {
       expect(material.shape, shape);
       expect(material.animationDuration, animationDuration);
       expect(tester.getSize(find.byType(ElevatedButton)), const Size(200, 200));
+      final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+      expect(align.alignment, alignment);
     }
 
     testWidgets('Button style overrides defaults', (WidgetTester tester) async {

packages/flutter/test/material/outlined_button_test.dart

@@ -52,6 +52,9 @@ void main() {
     expect(material.textStyle!.fontWeight, FontWeight.w500);
     expect(material.type, MaterialType.button);
 
+    final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+    expect(align.alignment, Alignment.center);
+
     final Offset center = tester.getCenter(find.byType(OutlinedButton));
     final TestGesture gesture = await tester.startGesture(center);
     await tester.pump(); // start the splash animation

packages/flutter/test/material/outlined_button_theme_test.dart

@@ -44,6 +44,9 @@ void main() {
     expect(material.textStyle!.fontFamily, 'Roboto');
     expect(material.textStyle!.fontSize, 14);
     expect(material.textStyle!.fontWeight, FontWeight.w500);
+
+    final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+    expect(align.alignment, Alignment.center);
   });
 
   group('[Theme, TextTheme, OutlinedButton style overrides]', () {
@@ -62,6 +65,7 @@ void main() {
     const MaterialTapTargetSize tapTargetSize = MaterialTapTargetSize.shrinkWrap;
     const Duration animationDuration = Duration(milliseconds: 25);
     const bool enableFeedback = false;
+    const AlignmentGeometry alignment = Alignment.centerLeft;
 
     final ButtonStyle style = OutlinedButton.styleFrom(
       primary: primaryColor,
@@ -79,6 +83,7 @@ void main() {
       tapTargetSize: tapTargetSize,
       animationDuration: animationDuration,
       enableFeedback: enableFeedback,
+      alignment: alignment,
     );
 
     Widget buildFrame({ ButtonStyle? buttonStyle, ButtonStyle? themeStyle, ButtonStyle? overallStyle }) {
@@ -140,6 +145,8 @@ void main() {
       expect(material.shape, shape);
       expect(material.animationDuration, animationDuration);
       expect(tester.getSize(find.byType(OutlinedButton)), const Size(200, 200));
+      final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+      expect(align.alignment, alignment);
     }
 
     testWidgets('Button style overrides defaults', (WidgetTester tester) async {

packages/flutter/test/material/text_button_test.dart

@@ -47,6 +47,9 @@ void main() {
     expect(material.textStyle!.fontWeight, FontWeight.w500);
     expect(material.type, MaterialType.button);
 
+    final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+    expect(align.alignment, Alignment.center);
+
     final Offset center = tester.getCenter(find.byType(TextButton));
     final TestGesture gesture = await tester.startGesture(center);
     await tester.pump(); // start the splash animation

packages/flutter/test/material/text_button_theme_test.dart

@@ -39,6 +39,9 @@ void main() {
     expect(material.textStyle!.fontFamily, 'Roboto');
     expect(material.textStyle!.fontSize, 14);
     expect(material.textStyle!.fontWeight, FontWeight.w500);
+
+    final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+    expect(align.alignment, Alignment.center);
   });
 
   group('[Theme, TextTheme, TextButton style overrides]', () {
@@ -57,6 +60,7 @@ void main() {
     const MaterialTapTargetSize tapTargetSize = MaterialTapTargetSize.shrinkWrap;
     const Duration animationDuration = Duration(milliseconds: 25);
     const bool enableFeedback = false;
+    const AlignmentGeometry alignment = Alignment.centerLeft;
 
     final ButtonStyle style = TextButton.styleFrom(
       primary: primaryColor,
@@ -74,6 +78,7 @@ void main() {
       tapTargetSize: tapTargetSize,
       animationDuration: animationDuration,
       enableFeedback: enableFeedback,
+      alignment: alignment,
     );
 
     Widget buildFrame({ ButtonStyle? buttonStyle, ButtonStyle? themeStyle, ButtonStyle? overallStyle }) {
@@ -135,6 +140,8 @@ void main() {
       expect(material.shape, shape);
       expect(material.animationDuration, animationDuration);
       expect(tester.getSize(find.byType(TextButton)), const Size(200, 200));
+      final Align align = tester.firstWidget<Align>(find.ancestor(of: find.text('button'), matching: find.byType(Align)));
+      expect(align.alignment, alignment);
     }
 
     testWidgets('Button style overrides defaults', (WidgetTester tester) async {