Utills - Flutter/Dart Utilities Package

A comprehensive Dart/Flutter utility package that provides reusable components to accelerate application development. This package includes structured failure handling, form validators, UI spacing utilities, pagination, and API response handling.

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Supported Platform:

Android, IOS, Web, Windows, macOS, Linux

📋 Table of Contents

🎯 Overview

Utills is designed to eliminate repetitive boilerplate code in Flutter/Dart applications. Whether you're building forms, handling API responses, managing pagination, or creating consistent UI spacing, this package provides battle-tested utilities that work out of the box.

Key Benefits:

  • ✅ Type-safe failure handling
  • ✅ Pre-built form validators with validation messages
  • ✅ Consistent UI spacing constants
  • ✅ Efficient pagination for large lists
  • ✅ Zero external dependencies (Flutter only)

📦 Installation

Add utills to your pubspec.yaml:

dependencies:
  utills: ^1.0.0

Then import the package in your Dart files:

import 'package:utills/utills.dart';

🚀 Features

1. Gaps (Spacing)

Predefined SizedBox constants for consistent vertical and horizontal spacing throughout your UI.

Available Gap Sizes:

Constant Size Type
vPad5, vPad10, vPad15, vPad20, vPad35 5-35px Vertical
hPad5, hPad10, hPad15, hPad20, hPad35 5-35px Horizontal
defaultPadding 16px Padding constant
defaultRadius 6px Border radius constant

Example:

import 'package:utills/gaps.dart';

Column(
  children: [
    Text("Title", style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold)),
    vPad10, // 10px vertical spacing
    Text("Subtitle", style: TextStyle(fontSize: 14)),
    vPad20, // 20px vertical spacing
    ElevatedButton(onPressed: () {}, child: Text("Submit")),
  ],
);

Row(
  children: [
    Icon(Icons.email),
    hPad10, // 10px horizontal spacing
    Text("user@example.com"),
  ],
);

// Use defaultPadding for consistent padding
Container(
  padding: EdgeInsets.all(defaultPadding), // 16px padding
  child: Text("Content"),
)

2. Validators

Form field validators to handle common validation scenarios with user-friendly error messages.

Available Validators:

Validator Purpose
fieldRequired() Ensures field is not empty
emailValidator() Validates email format
passwordRequired() Validates password with minimum length
confirmPasswordRequired() Matches password confirmation
usernameValidator() Validates username (alphanumeric + underscore)
phoneValidator() Validates phone number format
positiveNumberRequired() Ensures positive number input
integerValidator() Validates integer input
minLength() Checks minimum character length
maxLength() Checks maximum character length

Example:

import 'package:utills/validators.dart';

// In a TextFormField
TextFormField(
  decoration: InputDecoration(labelText: "Email"),
  validator: CommonValidator.emailValidator,
  // Returns "Email is required" or "Enter a valid email address" on error
),


TextFormField(
  decoration: InputDecoration(labelText: "Username"),
  validator: CommonValidator.usernameValidator,
  // Ensures 3+ characters with only letters, numbers, and underscores
),

3. API Handler & Failure Types

Structured, type-safe handling of API responses and errors using a Failure class and helper functions.

Core Concepts:

  • Attempt<T>: A tuple type (T?, Failure?) representing either a successful value or a failure
  • success<T>(value): Helper to create a successful attempt
  • failed<T>(failure): Helper to create a failed attempt
  • Failure<C>: Generic failure class with title, description, and code

Built-in Failure Types:

Failure Type HTTP Code Use Case
ServerFailure 500 Server-side errors
InternetFailure ~ No internet connection
TimeoutFailure 408 Request timeout
UnknownFailure -1 Unexpected errors
SessionExpired 401 User session expired
UnauthorizedFailure 401 User not authorized
ForbiddenFailure 403 Resource access forbidden
InvalidCredentialsFailure ~ Wrong username/password
BadRequestFailure 400 Invalid request parameters

Example:

import 'package:utills/api_handler.dart';
import 'package:utills/failure.dart';

// Define a function that returns Attempt
Future<Attempt<User>> fetchUser(int id) async {
  try {
    final response = await http.get(Uri.parse('https://api.example.com/users/$id'));
    
    if (response.statusCode == 200) {
      final user = User.fromJson(jsonDecode(response.body));
      return success(user);
    } else if (response.statusCode == 401) {
      return failed(SessionExpired());
    } else if (response.statusCode == 403) {
      return failed(ForbiddenFailure());
    } else {
      return failed(ServerFailure(code: response.statusCode));
    }
      }
       }

4. Paginator

Efficient pagination utilities for loading large lists incrementally. The package provides a lightweight, UI-friendly paginator (RestPaginator<T>) designed to work well with Flutter widgets and ChangeNotifier-based state management.

Key concepts

  • RestPageData<T>: simple container returned by your getPage callback. Typically contains items and an optional totalCount.
  • RestPaginator<T>: manages loaded pages, exposes loading state, and provides helpers to paginate, refresh and access loaded items.

API surface (common)

  • RestPageData<T>

    • List<T> items — the items returned for the page
    • int? totalCount — optional total number of items available on server

  • RestPaginator<T> (constructor)

    • RestPaginator({ required Future<RestPageData<T>> Function(int page, int pageSize) getPage, int pageSize = 20 })

Important properties:

  • int availableItemCount — number of items currently loaded
  • int? totalItemCount — total items reported by server (nullable)
  • bool isPaginating — whether a page load is in progress
  • bool endReached — true when all items are loaded

Common methods:

  • Future<void> paginate(int pageNumber) — load the requested page
  • Future<void> paginateNext() — convenience to load the next page
  • Future<void> refresh() — clear loaded pages and load first page
  • T getItem(int index) — get an item by absolute index
  • void dispose() — clean up listeners/resources

Typical getPage signature (example implementation):

class RestPageData<T> {
  final List<T> items;
  final int? totalCount;
  RestPageData({required this.items, this.totalCount});
}

// Example getPage implementation
Future<RestPageData<Map<String, dynamic>>> fetchUsersPage(int page, int pageSize) async {
  final response = await http.get(Uri.parse('https://api.example.com/users?page=$page&pageSize=$pageSize'));
  final body = jsonDecode(response.body) as Map<String, dynamic>;
  final items = (body['data'] as List).cast<Map<String, dynamic>>();
  final total = body['total'] as int?;
  return RestPageData(items: items, totalCount: total);
}

Using RestPaginator in a Flutter widget

final paginator = RestPaginator<Map<String, dynamic>>(
  getPage: fetchUsersPage,
  pageSize: 20,
);

// load first page (e.g., in initState)
await paginator.paginate(1);

// ListView with infinite scroll
ListView.builder(
  itemCount: paginator.availableItemCount + (paginator.endReached ? 0 : 1),
  itemBuilder: (context, index) {
    if (index >= paginator.availableItemCount) {
      // trigger load next page
      paginator.paginateNext();
      return const Center(child: CircularProgressIndicator());
    }

    final item = paginator.getItem(index);
    return ListTile(title: Text(item['name'] ?? ''));
  },
);

// Refreshing
await paginator.refresh();

// Dispose when no longer needed
paginator.dispose();

Notes and best practices

  • Keep getPage resilient: handle network errors and return an empty RestPageData or rethrow for the paginator to handle.
  • Use paginateNext() in UI scroll handlers to keep the code simple.
  • Expose the paginator from a ChangeNotifier (or provider) so UI widgets rebuild on state changes (e.g., isPaginating, availableItemCount).

5. Log

Developer-friendly logging utilities that print colorized messages in debug terminals and provide quick inspection and timing helpers.

What it provides:

  • Colorized log helpers for common levels: Log.success(), Log.error(), Log.info(), Log.warn(),Log.trace().
  • All methods are no-ops in release builds (only active during development/debug).

Example usage:

import 'package:utills/utills.dart';

// Colored logging
Log.success('Operation completed'); // appears green in debug terminal
Log.error('Failed to save record', error: e); // appears red
Log.info('Loading user', data: {'id': 1});
Log.warn('Deprecated API used');
Log.trace('Deprecated API used');

6. CustomToast

A lightweight, highly customizable Flutter package for displaying floating toast notifications with support for Success, Error, and Warning states.

⚙️ Initialization: To use CustomToast anywhere in your app without needing BuildContext, you must initialize it with your scaffoldMessengerKey in your main.dart.


final GlobalKey<ScaffoldMessengerState> messengerKey = GlobalKey<ScaffoldMessengerState>();

// optional
final myConfig = CustomToastConfig(
  backgroundColors: {
    ToastType.success: Colors.blueAccent,
    ToastType.error: Colors.deepPurple,
    ToastType.warning: Colors.amber,
  },
  borderRadius: BorderRadius.circular(20),
  duration: const Duration(seconds: 2),
);




void main() {
  // Initialize the package with default settings
  CustomToast.init(messengerKey: messengerKey);


  // Initialize with custom config
  CustomToast.init(
    messengerKey: messengerKey, 
    config: myConfig,
  );
  
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      scaffoldMessengerKey: messengerKey, // <--- Crucial step
      home: const HomeScreen(),
    );
  }
}

Usage: Trigger a toast notification from anywhere in your business logic or UI:

// Success Toast
CustomToast.show("Data saved successfully!", type: ToastType.success);

// Error Toast
CustomToast.show("Failed to connect to server.", type: ToastType.error);

// Warning Toast
CustomToast.show("Your subscription expires soon!", type: ToastType.warning);

Key Features - Decoupled Architecture: No BuildContext required for show() calls.

- Three Built-in States: Standardized support for success, error, and warning.

- Global Theming: Easily override default colors and styles to match your design system.

- Clean API: Optimized for readability and ease of use in large-scale applications.

7. Navigation Helper

Simplify your routing logic with the Maps utility class. No more boilerplate MaterialPageRoute required.

Features:

  • Maps.push: Standard navigation to a new screen.

  • Maps.pushReplacement: Replace the current screen (e.g., after login).

  • Maps.pushAndRemoveUntil: Clear the stack and go to a new screen (e.g., after logout).

  // Navigate to a new page
Navigate.push(context, const ProfileScreen());

// Replace the current page (Removes 'this' page from history)
Navigate.pushReplacement(context, const HomeScreen());

// Clear all routes and go to a new screen
Navigate.pushAndRemoveUntil(context, const WelcomeScreen());

This project is licensed under the MIT License - see the LICENSE file for details.

Usage Examples

A single, compact example demonstrating the core utilities included in utills.

import 'package:flutter/material.dart';
import 'package:utills/utills.dart';

void main() async {
  // Gaps: use constants in widgets
  final spacing = vPad10;

  // Validators
  final emailError = CommonValidator.emailValidator('user@example.com');

  // API handler / failures (illustrative)
  final attempt = success({'id': 1, 'name': 'Alice'});
  if (attempt.item != null) {
    Log.success('Loaded user: ${attempt.item}');
  } else {
    Log.error('Failure: ${attempt.failure}');
  }

  // Paginator (simplified)
  final paginator = RestPaginator<Map<String, dynamic>>(
    getPage: (page, pageSize) async {
      // Replace with real network call; return RestPageData(items, totalCount)
      return RestPageData(items: List.generate(5, (i) => {'index': i}), totalCount: 100);
    },
  );
  await paginator.paginate(1);
  Log.info('Loaded ${paginator.availableItemCount} items');

  // Log utilities
  Log.inspect({'spacing': spacing});
}

Made with ❤️ for Flutter developers by Hasibul Hasan Tushar

Libraries

utills