Card elevation example for Flutter issue #132199 https://github.com/flutter/flutter/issues/132199

main.dart

// MIT License
//
// Copyright (c) 2023 Mike Rydstrom
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

// This issue reported here: https://github.com/flutter/flutter/issues/132199

// A seed color for the M3 ColorScheme.
const Color seedColor = Color(0xFF6750A4);
// Make M3 ColorSchemes from a seed color.
final ColorScheme schemeLight = ColorScheme.fromSeed(
  brightness: Brightness.light,
  seedColor: seedColor,
);
final ColorScheme schemeDark = ColorScheme.fromSeed(
  brightness: Brightness.dark,
  seedColor: seedColor,
);

// Example theme
ThemeData theme(ThemeMode mode, ThemeSettings settings) {
  final ColorScheme colorScheme =
      mode == ThemeMode.light ? schemeLight : schemeDark;

  return ThemeData(
    colorScheme: colorScheme,
    useMaterial3: settings.useMaterial3,
    visualDensity: VisualDensity.standard,
  );
}

void main() {
  runApp(const IssueDemoApp());
}

class IssueDemoApp extends StatefulWidget {
  const IssueDemoApp({super.key});

  @override
  State<IssueDemoApp> createState() => _IssueDemoAppState();
}

class _IssueDemoAppState extends State<IssueDemoApp> {
  ThemeMode themeMode = ThemeMode.light;
  bool longLabel = false;
  TextDirection textDirection = TextDirection.ltr;
  ThemeSettings settings = const ThemeSettings(
    useMaterial3: true,
    useCustomTheme: false,
  );

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      themeMode: themeMode,
      theme: theme(ThemeMode.light, settings),
      darkTheme: theme(ThemeMode.dark, settings),
      home: Directionality(
        textDirection: textDirection,
        child: Scaffold(
          appBar: AppBar(
            title: settings.useMaterial3
                ? const Text("Card elevation (Material 3)")
                : const Text("Card elevation (Material 2)"),
            actions: [
              IconButton(
                icon: settings.useMaterial3
                    ? const Icon(Icons.filter_3)
                    : const Icon(Icons.filter_2),
                onPressed: () {
                  setState(() {
                    settings =
                        settings.copyWith(useMaterial3: !settings.useMaterial3);
                  });
                },
                tooltip: "Switch to Material ${settings.useMaterial3 ? 2 : 3}",
              ),
              IconButton(
                icon: themeMode == ThemeMode.dark
                    ? const Icon(Icons.wb_sunny_outlined)
                    : const Icon(Icons.wb_sunny),
                onPressed: () {
                  setState(() {
                    if (themeMode == ThemeMode.light) {
                      themeMode = ThemeMode.dark;
                    } else {
                      themeMode = ThemeMode.light;
                    }
                  });
                },
                tooltip: "Toggle brightness",
              ),
            ],
          ),
          body: HomePage(
            settings: settings,
            onSettings: (ThemeSettings value) {
              setState(() {
                settings = value;
              });
            },
          ),
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({
    super.key,
    required this.settings,
    required this.onSettings,
  });
  final ThemeSettings settings;
  final ValueChanged<ThemeSettings> onSettings;

  @override
  Widget build(BuildContext context) {
    return ListView(
      children: const [
        Padding(
          padding: EdgeInsets.all(16.0),
          child:
              Text('Example of Card with Elevation, Opacity, Tint and Shadow.'),
        ),
        SizedBox(height: 16),
        CardShowCase(),
        SizedBox(height: 16),
        Padding(
          padding: EdgeInsets.all(16.0),
          child: ShowColorSchemeColors(),
        ),
      ],
    );
  }
}

class CardShowCase extends StatefulWidget {
  const CardShowCase({super.key});

  @override
  State<CardShowCase> createState() => _CardShowCaseState();
}

class _CardShowCaseState extends State<CardShowCase> {
  double opacity = 1.0;
  double elevation = 9;
  bool isTinted = true;
  bool hasShadow = true;
  bool hasCustomBackground = true;
  bool hasCustomTint = true;
  bool hasCustomShadow = true;
  //
  Color cardColor = Colors.blueAccent;
  Color? shadowColor = Colors.cyan;
  Color? tintColor = Colors.red;

  @override
  Widget build(BuildContext context) {
    ColorScheme colors = Theme.of(context).colorScheme;

    return Column(
      children: <Widget>[
        ListTile(
          title: const Text('Opacity'),
          subtitle: Slider(
            min: 0.0,
            max: 1.0,
            divisions: 50,
            value: opacity,
            label: opacity.toStringAsFixed(2),
            onChanged: (double newValue) {
              setState(() {
                opacity = newValue;
              });
            },
          ),
          trailing: Text(opacity.toStringAsFixed(2)),
        ),
        ListTile(
          title: const Text('Elevation'),
          subtitle: Slider(
            min: 0.0,
            max: 20.0,
            divisions: 40,
            value: elevation,
            label: elevation.toStringAsFixed(1),
            onChanged: (double newValue) {
              setState(() {
                elevation = newValue;
              });
            },
          ),
          trailing: Text(elevation.toStringAsFixed(1)),
        ),
        SwitchListTile(
          title: const Text('Use custom blue accent background?'),
          subtitle: const Text('OFF=scheme.surface  ON=Colors.blueAccent'),
          value: hasCustomBackground,
          onChanged: (bool newValue) {
            setState(() {
              hasCustomBackground = newValue;
              if (hasCustomBackground) {
                cardColor = Colors.blueAccent;
              } else {
                cardColor = colors.surface;
              }
            });
          },
        ),
        SwitchListTile(
          title: const Text('Is tinted?'),
          subtitle: const Text('OFF=transparent  ON=setting below'),
          value: isTinted,
          onChanged: (bool newValue) {
            setState(() {
              isTinted = newValue;
              if (!isTinted) {
                tintColor = Colors.transparent;
              } else {
                if (hasCustomTint) {
                  tintColor = Colors.red;
                } else {
                  tintColor = null;
                }
              }
            });
          },
        ),
        SwitchListTile(
          title: const Text('Use custom red tint?'),
          subtitle: const Text('OFF=null=scheme.primary  ON=Colors.red'),
          value: hasCustomTint && isTinted,
          onChanged: isTinted
              ? (bool newValue) {
                  setState(() {
                    hasCustomTint = newValue;
                    if (!isTinted) {
                      tintColor = Colors.transparent;
                    } else {
                      if (hasCustomTint) {
                        tintColor = Colors.red;
                      } else {
                        tintColor = null;
                      }
                    }
                  });
                }
              : null,
        ),
        SwitchListTile(
          title: const Text('Has shadow?'),
          subtitle: const Text('OFF=transparent  ON=setting below'),
          value: hasShadow,
          onChanged: (bool newValue) {
            setState(() {
              hasShadow = newValue;
              if (!hasShadow) {
                shadowColor = Colors.transparent;
              } else {
                if (hasCustomShadow) {
                  shadowColor = Colors.cyan;
                } else {
                  shadowColor = Colors.black;
                }
              }
            });
          },
        ),
        SwitchListTile(
          title: const Text('Use custom cyan shadow?'),
          subtitle: const Text('OFF=null=scheme.shadow  ON=Colors.cyan'),
          value: hasShadow && hasCustomShadow,
          onChanged: (bool newValue) {
            setState(() {
              hasCustomShadow = newValue;
              if (!hasShadow) {
                shadowColor = Colors.transparent;
              } else {
                if (hasCustomShadow) {
                  shadowColor = Colors.cyan;
                } else {
                  shadowColor = null;
                }
              }
            });
          },
        ),
        Wrap(
          spacing: 20,
          children: [
            Card(
              elevation: 0,
              color: cardColor.withOpacity(opacity),
              surfaceTintColor: tintColor,
              shadowColor: shadowColor,
              child: const SizedBox(
                width: 150,
                height: 150,
                child: Center(
                  child: Text('Card\nElevation 0'),
                ),
              ),
            ),
            Card(
              elevation: elevation,
              color: cardColor.withOpacity(opacity),
              surfaceTintColor: tintColor,
              shadowColor: shadowColor,
              child: SizedBox(
                width: 150,
                height: 150,
                child: Center(
                  child:
                      Text('Card\nElevation\n${elevation.toStringAsFixed(2)}'),
                ),
              ),
            ),
            DecoratedBox(
              decoration: BoxDecoration(
                color: cardColor.withOpacity(opacity),
              ),
              child: const SizedBox(
                width: 150,
                height: 150,
                child: Center(
                  child: Text('DecoratedBox\nNo elevation'),
                ),
              ),
            ),
          ],
        ),
      ],
    );
  }
}

/// A Theme Settings class to bundle properties we want to modify on our
/// theme interactively.
@immutable
class ThemeSettings with Diagnosticable {
  final bool useMaterial3;
  final bool useCustomTheme;

  const ThemeSettings({
    required this.useMaterial3,
    required this.useCustomTheme,
  });

  /// Flutter debug properties override, includes toString.
  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<bool>('useMaterial3', useMaterial3));
    properties.add(DiagnosticsProperty<bool>('useCustomTheme', useCustomTheme));
  }

  /// Copy the object with one or more provided properties changed.
  ThemeSettings copyWith({
    bool? useMaterial3,
    bool? useCustomTheme,
    bool? useIndicatorWidth,
    bool? useTileHeight,
  }) {
    return ThemeSettings(
      useMaterial3: useMaterial3 ?? this.useMaterial3,
      useCustomTheme: useCustomTheme ?? this.useCustomTheme,
    );
  }

  /// Override the equality operator.
  @override
  bool operator ==(Object other) {
    if (identical(this, other)) return true;
    if (other.runtimeType != runtimeType) return false;
    return other is ThemeSettings &&
        other.useMaterial3 == useMaterial3 &&
        other.useCustomTheme == useCustomTheme;
  }

  /// Override for hashcode, dart.ui Jenkins based.
  @override
  int get hashCode => Object.hashAll(<Object?>[
        useMaterial3.hashCode,
        useCustomTheme.hashCode,
      ]);
}

/// Draw a number of boxes showing the colors of key theme color properties
/// in the ColorScheme of the inherited ThemeData and its color properties.
class ShowColorSchemeColors extends StatelessWidget {
  const ShowColorSchemeColors({super.key, this.onBackgroundColor});

  /// The color of the background the color widget are being drawn on.
  ///
  /// Some of the theme colors may have semi transparent fill color. To compute
  /// a legible text color for the sum when it shown on a background color, we
  /// need to alpha merge it with background and we need the exact background
  /// color it is drawn on for that. If not passed in from parent, it is
  /// assumed to be drawn on card color, which usually is close enough.
  final Color? onBackgroundColor;

  // Return true if the color is light, meaning it needs dark text for contrast.
  static bool _isLight(final Color color) =>
      ThemeData.estimateBrightnessForColor(color) == Brightness.light;

  // On color used when a theme color property does not have a theme onColor.
  static Color _onColor(final Color color, final Color bg) =>
      _isLight(Color.alphaBlend(color, bg)) ? Colors.black : Colors.white;

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colorScheme = theme.colorScheme;
    final bool useMaterial3 = theme.useMaterial3;
    const double spacing = 4;

    // Grab the card border from the theme card shape
    ShapeBorder? border = theme.cardTheme.shape;
    // If we had one, copy in a border side to it.
    if (border is RoundedRectangleBorder) {
      border = border.copyWith(
        side: BorderSide(
          color: colorScheme.outlineVariant,
          width: 1,
        ),
      );
      // If
    } else {
      // If border was null, make one matching Card default, but with border
      // side, if it was not null, we leave it as it was.
      border ??= RoundedRectangleBorder(
        borderRadius: BorderRadius.all(Radius.circular(useMaterial3 ? 12 : 4)),
        side: BorderSide(
          color: colorScheme.outlineVariant,
          width: 1,
        ),
      );
    }

    // Get effective background color.
    final Color background =
        onBackgroundColor ?? theme.cardTheme.color ?? theme.cardColor;

    // Wrap this widget branch in a custom theme where card has a border outline
    // if it did not have one, but retains its ambient themed border radius.
    return Theme(
      data: Theme.of(context).copyWith(
        cardTheme: CardTheme.of(context).copyWith(
          elevation: 0,
          surfaceTintColor: Colors.transparent,
          shape: border,
        ),
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          Padding(
            padding: const EdgeInsets.symmetric(vertical: 8),
            child: Text(
              'ColorScheme Colors',
              style: theme.textTheme.titleMedium,
            ),
          ),
          Wrap(
            alignment: WrapAlignment.start,
            crossAxisAlignment: WrapCrossAlignment.center,
            spacing: spacing,
            runSpacing: spacing,
            children: <Widget>[
              ColorCard(
                label: 'Primary',
                color: colorScheme.primary,
                textColor: colorScheme.onPrimary,
              ),
              ColorCard(
                label: 'on\nPrimary',
                color: colorScheme.onPrimary,
                textColor: colorScheme.primary,
              ),
              ColorCard(
                label: 'Primary\nContainer',
                color: colorScheme.primaryContainer,
                textColor: colorScheme.onPrimaryContainer,
              ),
              ColorCard(
                label: 'onPrimary\nContainer',
                color: colorScheme.onPrimaryContainer,
                textColor: colorScheme.primaryContainer,
              ),
              ColorCard(
                label: 'Secondary',
                color: colorScheme.secondary,
                textColor: colorScheme.onSecondary,
              ),
              ColorCard(
                label: 'on\nSecondary',
                color: colorScheme.onSecondary,
                textColor: colorScheme.secondary,
              ),
              ColorCard(
                label: 'Secondary\nContainer',
                color: colorScheme.secondaryContainer,
                textColor: colorScheme.onSecondaryContainer,
              ),
              ColorCard(
                label: 'on\nSecondary\nContainer',
                color: colorScheme.onSecondaryContainer,
                textColor: colorScheme.secondaryContainer,
              ),
              ColorCard(
                label: 'Tertiary',
                color: colorScheme.tertiary,
                textColor: colorScheme.onTertiary,
              ),
              ColorCard(
                label: 'on\nTertiary',
                color: colorScheme.onTertiary,
                textColor: colorScheme.tertiary,
              ),
              ColorCard(
                label: 'Tertiary\nContainer',
                color: colorScheme.tertiaryContainer,
                textColor: colorScheme.onTertiaryContainer,
              ),
              ColorCard(
                label: 'on\nTertiary\nContainer',
                color: colorScheme.onTertiaryContainer,
                textColor: colorScheme.tertiaryContainer,
              ),
              ColorCard(
                label: 'Error',
                color: colorScheme.error,
                textColor: colorScheme.onError,
              ),
              ColorCard(
                label: 'on\nError',
                color: colorScheme.onError,
                textColor: colorScheme.error,
              ),
              ColorCard(
                label: 'Error\nContainer',
                color: colorScheme.errorContainer,
                textColor: colorScheme.onErrorContainer,
              ),
              ColorCard(
                label: 'onError\nContainer',
                color: colorScheme.onErrorContainer,
                textColor: colorScheme.errorContainer,
              ),
              ColorCard(
                label: 'Background',
                color: colorScheme.background,
                textColor: colorScheme.onBackground,
              ),
              ColorCard(
                label: 'on\nBackground',
                color: colorScheme.onBackground,
                textColor: colorScheme.background,
              ),
              ColorCard(
                label: 'Surface',
                color: colorScheme.surface,
                textColor: colorScheme.onSurface,
              ),
              ColorCard(
                label: 'on\nSurface',
                color: colorScheme.onSurface,
                textColor: colorScheme.surface,
              ),
              ColorCard(
                label: 'Surface\nVariant',
                color: colorScheme.surfaceVariant,
                textColor: colorScheme.onSurfaceVariant,
              ),
              ColorCard(
                label: 'onSurface\nVariant',
                color: colorScheme.onSurfaceVariant,
                textColor: colorScheme.surfaceVariant,
              ),
              ColorCard(
                label: 'Outline',
                color: colorScheme.outline,
                textColor: colorScheme.background,
              ),
              ColorCard(
                label: 'Outline\nVariant',
                color: colorScheme.outlineVariant,
                textColor: colorScheme.onBackground,
              ),
              ColorCard(
                label: 'Shadow',
                color: colorScheme.shadow,
                textColor: _onColor(colorScheme.shadow, background),
              ),
              ColorCard(
                label: 'Scrim',
                color: colorScheme.scrim,
                textColor: _onColor(colorScheme.scrim, background),
              ),
              ColorCard(
                label: 'Inverse\nSurface',
                color: colorScheme.inverseSurface,
                textColor: colorScheme.onInverseSurface,
              ),
              ColorCard(
                label: 'onInverse\nSurface',
                color: colorScheme.onInverseSurface,
                textColor: colorScheme.inverseSurface,
              ),
              ColorCard(
                label: 'Inverse\nPrimary',
                color: colorScheme.inversePrimary,
                textColor: colorScheme.inverseSurface,
              ),
              ColorCard(
                label: 'Surface\nTint',
                color: colorScheme.surfaceTint,
                textColor: colorScheme.onPrimary,
              ),
            ],
          ),
        ],
      ),
    );
  }
}

/// A [SizedBox] with a [Card] and string text in it. Used in this demo to
/// display theme color boxes.
///
/// Can specify label text color and background color.
class ColorCard extends StatelessWidget {
  const ColorCard({
    super.key,
    required this.label,
    required this.color,
    required this.textColor,
    this.size,
  });

  final String label;
  final Color color;
  final Color textColor;
  final Size? size;

  @override
  Widget build(BuildContext context) {
    const double fontSize = 11;
    const Size effectiveSize = Size(86, 58);

    return SizedBox(
      width: effectiveSize.width,
      height: effectiveSize.height,
      child: Card(
        margin: EdgeInsets.zero,
        clipBehavior: Clip.antiAlias,
        color: color,
        child: Center(
          child: Text(
            label,
            style: TextStyle(color: textColor, fontSize: fontSize),
            textAlign: TextAlign.center,
          ),
        ),
      ),
    );
  }
}

Card elevation example for Flutter issue #132199 flutter/flutter#132199