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Flutter Mobile Development · レッスン

レスポンシブなタイポグラフィとコンポーネントテーマ

テキストを拡縮し、コンポーネントテーマをカスタマイズして、デバイスをまたいだ一貫したブランド表現を実現します。

「レスポンシブなタイポグラフィとコンポーネントテーマ」はCoddyKit上の無料Flutter Mobile Developmentレッスンです。 これはレッスン4/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはFlutter Mobile Development学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Flutter Mobile Developmentコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Why Typography Scales

A design system keeps your app's look consistent across phones, foldables, and tablets. Two pillars hold it together: typography (how text looks at every size) and component theming (how buttons, cards, and inputs are styled once and reused everywhere).

In Material 3, both live inside ThemeData. Instead of styling each widget by hand, you define the rules centrally and let widgets inherit them. This lesson shows how to scale text responsively and customize component themes for consistent cross-device branding.

  • TextTheme carries the type scale (display, headline, title, body, label).
  • Component themes (e.g. ElevatedButtonThemeData) shape each widget family.

The Material 3 Type Scale

Material 3 defines a type scale of 15 named styles grouped into 5 roles. Each role has Large, Medium, and Small variants:

  • displayLarge/Medium/Small — big, expressive hero text.
  • headlineLarge/Medium/Small — section headers.
  • titleLarge/Medium/Small — list and dialog titles.
  • bodyLarge/Medium/Small — paragraphs and main content.
  • labelLarge/Medium/Small — buttons, captions, chips.

You read these from context anywhere in your widget tree, so a heading always matches the same scale no matter where it appears.

Widget build(BuildContext context) {
  final textTheme = Theme.of(context).textTheme;
  return Column(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: [
      Text('Welcome', style: textTheme.displaySmall),
      Text('Your daily summary', style: textTheme.titleMedium),
      Text('Here is what happened today.', style: textTheme.bodyMedium),
    ],
  );
}

Customizing the TextTheme

To brand your typography, override the textTheme on ThemeData. A clean approach is to start from a base text theme and copyWith only the styles you want to change. This keeps the rest of the Material defaults intact.

Notice how each style is a TextStyle with explicit fontSize, fontWeight, and letterSpacing. Defining them in one place guarantees consistency across every screen.

final ThemeData appTheme = ThemeData(
  useMaterial3: true,
  textTheme: const TextTheme(
    displaySmall: TextStyle(
      fontSize: 36,
      fontWeight: FontWeight.w700,
      letterSpacing: -0.5,
    ),
    titleMedium: TextStyle(
      fontSize: 16,
      fontWeight: FontWeight.w600,
    ),
    bodyMedium: TextStyle(
      fontSize: 14,
      height: 1.4,
    ),
  ),
);

Responsive Sizing with MediaQuery

Hard-coded font sizes look great on one device but cramped or oversized on another. Use MediaQuery to read the screen width and pick a scale factor. A common pattern: clamp a base size between a minimum and a maximum so text never gets absurdly small or large.

Here we compute a responsive headline size from the available width, then apply it on top of the theme's style with copyWith.

Widget build(BuildContext context) {
  final width = MediaQuery.of(context).size.width;
  // Scale headline between 24 and 40 based on width.
  final headlineSize = (width / 14).clamp(24.0, 40.0);
  final base = Theme.of(context).textTheme.headlineMedium;
  return Text(
    'Cross-device branding',
    style: base?.copyWith(fontSize: headlineSize),
  );
}

Respecting the User's Text Scale

Accessibility matters: users can enlarge system text. In modern Flutter, read this via MediaQuery.textScalerOf(context), which returns a TextScaler. Avoid disabling it outright; instead clamp it so very large settings don't break your layout while still honoring the user's preference.

Wrap a subtree in MediaQuery with a clamped scaler to bound the growth.

Widget build(BuildContext context) {
  final scaler = MediaQuery.textScalerOf(context)
      .clamp(minScaleFactor: 1.0, maxScaleFactor: 1.6);
  return MediaQuery(
    data: MediaQuery.of(context).copyWith(textScaler: scaler),
    child: const Text('Readable yet bounded'),
  );
}

A Pure-Dart Responsive Helper

The scaling logic itself is plain Dart and easy to unit-test in isolation, no Flutter needed. Below is a small function that maps a screen width to a font size with a linear ramp between two breakpoints, then clamps the result. Testing this pure logic separately keeps your widgets thin.

double responsiveFontSize(
  double width, {
  double minWidth = 320,
  double maxWidth = 840,
  double minSize = 14,
  double maxSize = 22,
}) {
  if (width <= minWidth) return minSize;
  if (width >= maxWidth) return maxSize;
  final t = (width - minWidth) / (maxWidth - minWidth);
  return minSize + t * (maxSize - minSize);
}

void main() {
  print(responsiveFontSize(300)); // 14.0 (clamped)
  print(responsiveFontSize(580)); // ~17.0
  print(responsiveFontSize(900)); // 22.0 (clamped)
}

Introducing Component Themes

Beyond text, Material 3 lets you theme entire widget families centrally. Each has a dedicated *ThemeData slot on ThemeData:

  • elevatedButtonTheme, filledButtonTheme, textButtonTheme
  • cardTheme, chipTheme, appBarTheme
  • inputDecorationTheme for text fields

Set them once and every matching widget inherits the styling. This is the heart of a design system: change the brand in one file, see it everywhere.

Theming Elevated Buttons

Use ElevatedButtonThemeData with a ButtonStyle to standardize padding, shape, and text style for every ElevatedButton in the app. Tying the button's label style back to labelLarge keeps it aligned with your type scale.

Because the theme supplies these defaults, individual buttons stay clean: ElevatedButton(onPressed: ..., child: Text('Save')) with no inline styling.

final elevatedButtonTheme = ElevatedButtonThemeData(
  style: ElevatedButton.styleFrom(
    padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 14),
    shape: RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(12),
    ),
    textStyle: const TextStyle(
      fontSize: 15,
      fontWeight: FontWeight.w600,
    ),
  ),
);

Theming Cards and Inputs

Cards and text fields are everywhere in mobile UIs, so theming them pays off fast. CardThemeData controls elevation, shape, and margin; InputDecorationTheme standardizes borders, fills, and label behavior for every TextField.

With these in place, a form looks consistent across the app without repeating decoration code on each field.

final cardTheme = CardThemeData(
  elevation: 1,
  margin: const EdgeInsets.all(8),
  shape: RoundedRectangleBorder(
    borderRadius: BorderRadius.circular(16),
  ),
);

final inputDecorationTheme = InputDecorationTheme(
  filled: true,
  contentPadding: const EdgeInsets.all(16),
  border: OutlineInputBorder(
    borderRadius: BorderRadius.circular(12),
    borderSide: BorderSide.none,
  ),
);

Assembling the Full ThemeData

Now combine typography and component themes into a single ThemeData. Pairing it with a ColorScheme.fromSeed gives you a coherent Material 3 palette. Pass this theme to MaterialApp(theme: ...) and the whole app picks it up.

This one object is your design system's source of truth: brand colors, type scale, and component styling, all together.

ThemeData buildBrandTheme() {
  return ThemeData(
    useMaterial3: true,
    colorScheme: ColorScheme.fromSeed(seedColor: const Color(0xFF6750A4)),
    textTheme: const TextTheme(
      titleMedium: TextStyle(fontSize: 16, fontWeight: FontWeight.w600),
      bodyMedium: TextStyle(fontSize: 14, height: 1.4),
    ),
    elevatedButtonTheme: ElevatedButtonThemeData(
      style: ElevatedButton.styleFrom(
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(12),
        ),
      ),
    ),
    cardTheme: CardThemeData(
      elevation: 1,
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(16),
      ),
    ),
  );
}

Reading the Theme in Widgets

Once the theme is set, widgets should pull styling from it rather than hard-coding values. Use Theme.of(context) to access the textTheme, colorScheme, and any component theme.

This makes your widgets theme-agnostic: switch to a dark theme or rebrand, and they update automatically because they never assumed a specific color or size.

Widget build(BuildContext context) {
  final theme = Theme.of(context);
  return Card(
    child: Padding(
      padding: const EdgeInsets.all(16),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Text('Account', style: theme.textTheme.titleMedium),
          const SizedBox(height: 8),
          Text(
            'Manage your profile and settings.',
            style: theme.textTheme.bodyMedium?.copyWith(
              color: theme.colorScheme.onSurfaceVariant,
            ),
          ),
        ],
      ),
    ),
  );
}

Quick Check

You want every TextField in your app to share the same rounded, filled border without repeating decoration code on each field. Which approach fits a Material 3 design system best?

Recap

You built the typography and component foundation of a Material 3 design system:

  • Type scale: the 15 named styles (display, headline, title, body, label) read via Theme.of(context).textTheme.
  • Custom TextTheme: override fonts and sizes centrally with copyWith.
  • Responsive sizing: derive sizes from MediaQuery width and clamp them, and respect (but bound) the user's textScaler for accessibility.
  • Component themes: ElevatedButtonThemeData, CardThemeData, and InputDecorationTheme style entire widget families once.
  • Single source of truth: assemble everything into one ThemeData with ColorScheme.fromSeed, then read it in theme-agnostic widgets.

The result is consistent cross-device branding that adapts to screen size and user preferences without per-widget styling.

よくある質問

「レスポンシブなタイポグラフィとコンポーネントテーマ」レッスンは無料ですか？

はい。「レスポンシブなタイポグラフィとコンポーネントテーマ」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Flutter Mobile Developmentコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Flutter Mobile Developmentコースには全4レッスンが含まれています。

「レスポンシブなタイポグラフィとコンポーネントテーマ」で何を学びますか？

テキストを拡縮し、コンポーネントテーマをカスタマイズして、デバイスをまたいだ一貫したブランド表現を実現します。 ブラウザで直接実行するハンズオンコードでFlutter Mobile Developmentを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Flutter Mobile Developmentを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのFlutter Mobile Developmentは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン4/4です。

「レスポンシブなタイポグラフィとコンポーネントテーマ」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このFlutter Mobile Developmentレッスンでコードを書いて実行できますか？

はい。すべてのFlutter Mobile Developmentレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

  1. Material 3のカラースキームとシードカラー
  2. 動的カラーと適応型ライト／ダークテーマ
  3. ブランドトークン向けカスタムThemeExtension
  4. レスポンシブなタイポグラフィとコンポーネントテーマ
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