Add Widgetbook setup with theme configuration, analysis options, and initial component use cases

widgetbook/lib/split_button_m3e/INDEX-split_button_m3e.md

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+# Widgetbook Index — split_button_m3e
+
+This index summarizes all Widgetbook use cases defined for SplitButtonM3E.
+
+Component: SplitButtonM3E<T>
+
+Variants
+- default
+- filled
+- tonal
+- elevated
+- outlined
+- text
+- xs
+- sm
+- md
+- lg
+- xl
+- round
+- square
+- with_icon
+- with_label
+- long_label
+- many_items
+- empty_items
+- disabled
+
+Notes
+- Knobs provided for critical parameters: items count, selection (via choosing menu item), emphasis, size, shape, trailingAlignment, enabled, tooltips, and content (label/icon).
+- Callbacks print informative messages to the console when the primary action is pressed or a menu item is selected.
+- Complex objects use sensible defaults; see TODO comments for potential icon picker enhancement.

widgetbook/lib/split_button_m3e/split_button_m3e_usecase.dart

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+
+
+import 'package:flutter/material.dart';
+import 'package:widgetbook/widgetbook.dart';
+import 'package:widgetbook_annotation/widgetbook_annotation.dart' as widgetbook;
+import 'package:split_button_m3e/split_button_m3e.dart';
+
+Widget _buildSplitButtonDemo(
+  BuildContext context, {
+  SplitButtonM3EEmphasis? emphasisFixed,
+  SplitButtonM3ESize? sizeFixed,
+  SplitButtonM3EShape? shapeFixed,
+  bool? enabledFixed,
+  String? labelFixed,
+  IconData? iconFixed,
+  int? itemsFixedCount,
+}) {
+  final emphasis = emphasisFixed ??
+      context.knobs.object.dropdown<SplitButtonM3EEmphasis>(
+        label: 'emphasis',
+        initialOption: SplitButtonM3EEmphasis.filled,
+        options: SplitButtonM3EEmphasis.values,
+        labelBuilder: (v) => v.name,
+      );
+
+  final size = sizeFixed ?? context.knobs.object.dropdown<SplitButtonM3ESize>(
+    label: 'size',
+    initialOption: SplitButtonM3ESize.md,
+    options: SplitButtonM3ESize.values,
+    labelBuilder: (v) => v.name,
+  );
+
+  final shape = shapeFixed ??
+      context.knobs.object.dropdown<SplitButtonM3EShape>(
+        label: 'shape',
+        initialOption: SplitButtonM3EShape.round,
+        options: SplitButtonM3EShape.values,
+        labelBuilder: (v) => v.name,
+      );
+
+  final trailingAlignment = context.knobs.object
+      .dropdown<SplitButtonM3ETrailingAlignment>(
+    label: 'trailingAlignment',
+    initialOption: SplitButtonM3ETrailingAlignment.opticalCenter,
+    options: SplitButtonM3ETrailingAlignment.values,
+    labelBuilder: (v) => v.name,
+  );
+
+  final enabled = enabledFixed ??
+      context.knobs.boolean(label: 'enabled', initialValue: true);
+
+  // Content knobs
+  final effectiveLabel = labelFixed ??
+      context.knobs.string(label: 'label', initialValue: 'Save');
+
+  final includeIcon = iconFixed != null
+      ? true
+      : context.knobs.boolean(label: 'leadingIcon', initialValue: true);
+
+  final effectiveIcon = iconFixed ?? Icons.save_outlined; // TODO: icon picker knob
+
+  // Tooltips knobs (helpful for semantics and tests)
+  final leadingTooltip = context.knobs
+      .string(label: 'leadingTooltip', initialValue: 'Save');
+  final trailingTooltip = context.knobs
+      .string(label: 'trailingTooltip', initialValue: 'Open menu');
+
+  // Items knobs
+  final itemCount = itemsFixedCount ?? context.knobs.int.slider(
+    label: 'items count',
+    initialValue: 4,
+    min: 0,
+    max: 120,
+    divisions: 120,
+  );
+
+  final disableEveryNth = context.knobs.int.slider(
+    label: 'disable every Nth (0 = none)',
+    initialValue: 0,
+    min: 0,
+    max: 10,
+    divisions: 10,
+  );
+
+  final items = List.generate(itemCount, (i) {
+    final disabled = disableEveryNth == 0 ? false : (i % disableEveryNth == 0);
+    return SplitButtonM3EItem<String>(
+      value: 'value_$i',
+      child: 'Option $i',
+      enabled: !disabled,
+    );
+  });
+
+  return Center(
+    child: SplitButtonM3E<String>(
+      size: size,
+      shape: shape,
+      emphasis: emphasis,
+      label: effectiveLabel.isEmpty ? null : effectiveLabel,
+      leadingIcon: includeIcon ? effectiveIcon : null,
+      onPressed: enabled
+          ? () => print(
+              'Primary pressed: size=${size.name}, shape=${shape.name}, emphasis=${emphasis.name}',
+            )
+          : null,
+      items: items,
+      onSelected: (v) => print('Menu selected → $v'),
+      trailingAlignment: trailingAlignment,
+      leadingTooltip: leadingTooltip.isEmpty ? null : leadingTooltip,
+      trailingTooltip: trailingTooltip.isEmpty ? null : trailingTooltip,
+      enabled: enabled,
+    ),
+  );
+}
+
+// Default
+@widgetbook.UseCase(name: 'default', type: SplitButtonM3E)
+Widget buildSplitButtonM3EDefaultUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(context);
+}
+
+// Emphasis variants
+@widgetbook.UseCase(name: 'filled', type: SplitButtonM3E)
+Widget buildSplitButtonM3EFilledUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    emphasisFixed: SplitButtonM3EEmphasis.filled,
+  );
+}
+
+@widgetbook.UseCase(name: 'tonal', type: SplitButtonM3E)
+Widget buildSplitButtonM3ETonalUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    emphasisFixed: SplitButtonM3EEmphasis.tonal,
+  );
+}
+
+@widgetbook.UseCase(name: 'elevated', type: SplitButtonM3E)
+Widget buildSplitButtonM3EElevatedUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    emphasisFixed: SplitButtonM3EEmphasis.elevated,
+  );
+}
+
+@widgetbook.UseCase(name: 'outlined', type: SplitButtonM3E)
+Widget buildSplitButtonM3EOutlinedUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    emphasisFixed: SplitButtonM3EEmphasis.outlined,
+  );
+}
+
+@widgetbook.UseCase(name: 'text', type: SplitButtonM3E)
+Widget buildSplitButtonM3ETextUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    emphasisFixed: SplitButtonM3EEmphasis.text,
+  );
+}
+
+// Size variants
+@widgetbook.UseCase(name: 'xs', type: SplitButtonM3E)
+Widget buildSplitButtonM3EXSUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    sizeFixed: SplitButtonM3ESize.xs,
+  );
+}
+
+@widgetbook.UseCase(name: 'sm', type: SplitButtonM3E)
+Widget buildSplitButtonM3ESMUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    sizeFixed: SplitButtonM3ESize.sm,
+  );
+}
+
+@widgetbook.UseCase(name: 'md', type: SplitButtonM3E)
+Widget buildSplitButtonM3EMDUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    sizeFixed: SplitButtonM3ESize.md,
+  );
+}
+
+@widgetbook.UseCase(name: 'lg', type: SplitButtonM3E)
+Widget buildSplitButtonM3ELGUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    sizeFixed: SplitButtonM3ESize.lg,
+  );
+}
+
+@widgetbook.UseCase(name: 'xl', type: SplitButtonM3E)
+Widget buildSplitButtonM3EXLUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    sizeFixed: SplitButtonM3ESize.xl,
+  );
+}
+
+// Shape variants
+@widgetbook.UseCase(name: 'round', type: SplitButtonM3E)
+Widget buildSplitButtonM3ERoundUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    shapeFixed: SplitButtonM3EShape.round,
+  );
+}
+
+@widgetbook.UseCase(name: 'square', type: SplitButtonM3E)
+Widget buildSplitButtonM3ESquareUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    shapeFixed: SplitButtonM3EShape.square,
+  );
+}
+
+// Content variants
+@widgetbook.UseCase(name: 'with_icon', type: SplitButtonM3E)
+Widget buildSplitButtonM3EWithIconUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    labelFixed: '',
+    iconFixed: Icons.save_outlined,
+  );
+}
+
+@widgetbook.UseCase(name: 'with_label', type: SplitButtonM3E)
+Widget buildSplitButtonM3EWithLabelUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    labelFixed: 'Save',
+    iconFixed: null,
+  );
+}
+
+@widgetbook.UseCase(name: 'long_label', type: SplitButtonM3E)
+Widget buildSplitButtonM3ELongLabelUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    labelFixed: 'Save document and sync to cloud',
+    iconFixed: Icons.cloud_upload_outlined,
+  );
+}
+
+// Edge cases
+@widgetbook.UseCase(name: 'many_items', type: SplitButtonM3E)
+Widget buildSplitButtonM3EManyItemsUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    itemsFixedCount: 60,
+  );
+}
+
+@widgetbook.UseCase(name: 'empty_items', type: SplitButtonM3E)
+Widget buildSplitButtonM3EEmptyItemsUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    itemsFixedCount: 0,
+  );
+}
+
+@widgetbook.UseCase(name: 'disabled', type: SplitButtonM3E)
+Widget buildSplitButtonM3EDisabledUseCase(BuildContext context) {
+  return _buildSplitButtonDemo(
+    context,
+    enabledFixed: false,
+  );
+}