add-loading-indicator

Name: Add Loading Indicator
Author: marcglasberg

// Add loading state tracking to widgets using context.isWaiting() for spinners and skeletons

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updated:2026年1月29日 03:53

SKILL.md

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name	add-loading-indicator
description	Add loading state tracking to widgets using context.isWaiting() for spinners and skeletons

Add Loading Indicator with isWaiting()

This skill adds loading state tracking to widgets using context.isWaiting().

What This Skill Does

Shows loading indicators in widgets by:

Using context.isWaiting(key) to check if an operation is in progress
Displaying appropriate loading UI (spinner, skeleton, overlay)
Automatically updating when the operation completes

Instructions

Step 1: Ensure Cubit Uses mix()

The Cubit method must use mix() with a key:

class UserCubit extends Cubit<User> {
  void loadUser() => mix(
    key: this,  // Key used for tracking
    () async {
      final user = await api.getUser();
      emit(user);
    },
  );
}

Step 2: Add isWaiting() to Widget

Check context.isWaiting(key) in the widget's build method:

class UserScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Check if loading
    if (context.isWaiting(UserCubit)) {
      return const Center(
        child: CircularProgressIndicator(),
      );
    }

    // Show data
    final user = context.watch<UserCubit>().state;
    return Text('Hello, ${user.name}');
  }
}

Key Matching

The key in isWaiting() must match the key in mix():

// In Cubit
mix(key: this, ...)           // → context.isWaiting(UserCubit)
mix(key: UserCubit, ...)      // → context.isWaiting(UserCubit)
mix(key: 'loadUser', ...)     // → context.isWaiting('loadUser')
mix(key: LoadAction.user, ...)// → context.isWaiting(LoadAction.user)
mix(key: (UserCubit, id), ...)// → context.isWaiting((UserCubit, id))

Loading UI Patterns

Full Screen Replacement

Widget build(BuildContext context) {
  if (context.isWaiting(UserCubit)) {
    return const Center(child: CircularProgressIndicator());
  }
  return UserProfile();
}

Inline Loading Indicator

Widget build(BuildContext context) {
  return Column(
    children: [
      if (context.isWaiting(UserCubit))
        const LinearProgressIndicator(),
      UserProfile(),
    ],
  );
}

Overlay Loading

Widget build(BuildContext context) {
  return Stack(
    children: [
      UserProfile(),
      if (context.isWaiting(UserCubit))
        Container(
          color: Colors.black26,
          child: const Center(child: CircularProgressIndicator()),
        ),
    ],
  );
}

Button Loading State

Widget build(BuildContext context) {
  final isLoading = context.isWaiting(SaveUser);

  return ElevatedButton(
    onPressed: isLoading ? null : () => cubit.saveUser(user),
    child: isLoading
        ? const SizedBox(
            width: 20,
            height: 20,
            child: CircularProgressIndicator(strokeWidth: 2),
          )
        : const Text('Save'),
  );
}

Skeleton Loading

Widget build(BuildContext context) {
  if (context.isWaiting(ProductCubit)) {
    return ListView.builder(
      itemCount: 5,
      itemBuilder: (_, __) => const ProductSkeleton(),
    );
  }

  final products = context.watch<ProductCubit>().state.products;
  return ListView.builder(
    itemCount: products.length,
    itemBuilder: (_, i) => ProductCard(product: products[i]),
  );
}

Per-Item Loading

Widget build(BuildContext context) {
  return ListView.builder(
    itemCount: items.length,
    itemBuilder: (context, index) {
      final item = items[index];

      // Check loading for this specific item
      if (context.isWaiting((DeleteItem, item.id))) {
        return const ListTile(
          title: Text('Deleting...'),
          trailing: CircularProgressIndicator(),
        );
      }

      return ListTile(
        title: Text(item.name),
        trailing: IconButton(
          icon: const Icon(Icons.delete),
          onPressed: () => cubit.deleteItem(item.id),
        ),
      );
    },
  );
}

Multiple Loading States

Check Any of Multiple Keys

Widget build(BuildContext context) {
  final isLoading = context.isWaiting(LoadUsers) ||
                    context.isWaiting(LoadPosts);

  if (isLoading) {
    return const CircularProgressIndicator();
  }
  // ...
}

Different Indicators for Different Operations

Widget build(BuildContext context) {
  return Column(
    children: [
      // Header with user loading
      if (context.isWaiting(LoadUser))
        const LinearProgressIndicator()
      else
        UserHeader(),

      // Posts section with its own loading
      if (context.isWaiting(LoadPosts))
        const PostsSkeleton()
      else
        PostsList(),
    ],
  );
}

Complete Example

// Cubit with multiple operations
class ProfileCubit extends Cubit<ProfileState> {
  ProfileCubit() : super(const ProfileState());

  void loadProfile() => mix(
    key: LoadProfile,
    () async {
      final profile = await api.getProfile();
      emit(state.copyWith(profile: profile));
    },
  );

  void updateAvatar(File image) => mix(
    key: UpdateAvatar,
    () async {
      final url = await api.uploadAvatar(image);
      emit(state.copyWith(avatarUrl: url));
    },
  );

  void saveSettings(Settings settings) => mix(
    key: SaveSettings,
    () async {
      await api.saveSettings(settings);
      emit(state.copyWith(settings: settings));
    },
  );
}

// Widget with loading states
class ProfileScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Full screen loading for initial load
    if (context.isWaiting(LoadProfile)) {
      return const Scaffold(
        body: Center(child: CircularProgressIndicator()),
      );
    }

    final state = context.watch<ProfileCubit>().state;

    return Scaffold(
      body: Column(
        children: [
          // Avatar with overlay loading
          Stack(
            children: [
              CircleAvatar(backgroundImage: NetworkImage(state.avatarUrl)),
              if (context.isWaiting(UpdateAvatar))
                const Positioned.fill(
                  child: CircularProgressIndicator(),
                ),
            ],
          ),

          // Settings section
          SettingsForm(
            settings: state.settings,
            onSave: (s) => context.read<ProfileCubit>().saveSettings(s),
          ),

          // Save button with loading
          ElevatedButton(
            onPressed: context.isWaiting(SaveSettings)
                ? null
                : () => context.read<ProfileCubit>().saveSettings(state.settings),
            child: context.isWaiting(SaveSettings)
                ? const CircularProgressIndicator()
                : const Text('Save'),
          ),
        ],
      ),
    );
  }
}