Smart Input Formatters

A robust set of Flutter TextInputFormatters designed for financial applications.
Handle currency formatting, mathematical expressions, and auto-decimal shifting with industry-level cursor stability.

Features

  • 🧮 Expression Support
    Formats numbers dynamically even inside math expressions.
    Example: 1000+500 → 1,000+500.

  • 🎯 Cursor Stability
    Prevents cursor jumping by intelligently preserving selection position when separators are inserted or removed.

  • 🏦 Auto-Decimal Shifting
    Ideal for POS and banking apps.
    Example:

    • Typing 5 → 0.05
    • Typing 50 → 0.50

  • 🌍 Locale-Aware
    Fully configurable decimal and grouping separators to support any regional currency format.

  • 🧹 Clean Input
    Automatically normalizes mathematical operators and trims unnecessary leading zeros.
    Example:

    • x → *
    • 000123 → 123

Getting Started

Add the package to your pubspec.yaml:

dependencies:
  smart_input_formatters: ^0.0.1

Then import it:

import 'package:smart_input_formatters/smart_input_formatters.dart';

Usage

The easiest way to use this package is through the SmartAmountFormatter wrapper, which automatically manages the correct order of formatters.

Classic Calculator Mode

Use this for standard price inputs where you want thousands separators and math expression support.

TextFormField(
  inputFormatters: SmartAmountFormatter(
    decimalSep: '.',
    groupSep: ',',
    autoDec: false, // Default
  ).formatters,
  keyboardType: TextInputType.text,
  decoration: InputDecoration(
    labelText: 'Amount',
  ),
);

Example inputs:

Input Output
1000 1,000
1000+500 1,000+500
20000*3 20,000*3

Banking / Auto-Decimal Mode

Common in POS systems and banking applications where digits are entered continuously and the decimal shifts from the right.

TextFormField(
  inputFormatters: SmartAmountFormatter(
    decimalSep: '.',
    groupSep: ',',
    autoDec: true,
    decimalDigits: 2,
  ).formatters,
  keyboardType: TextInputType.number,
  decoration: InputDecoration(
    hintText: '0.00',
  ),
);

Example behavior:

Input Output
5 0.05
50 0.50
500 5.00
12345 123.45

How It Works (Formatting Pipeline)

SmartAmountFormatter runs a sequence of specialized formatters in a controlled pipeline to ensure clean and predictable input.

1. CalculatorNormalizer

Standardizes operators and separators.

Examples:

  • x → *
  • . ↔ , depending on locale

2. LeadingZeroIntegerTrimmer

Removes redundant leading zeros.

Examples:

  • 000123 → 123
  • 0000 → 0

3. AutoDecimalShiftFormatter (optional)

Applies fixed-point decimal shifting when autoDec is enabled.

Example with decimalDigits = 2:

Raw Input Output
5 0.05
50 0.50
500 5.00

4. GroupSeparatorFormatter

Injects thousands separators while preserving cursor position.

Examples:

Input Output
1000 1,000
1000000 1,000,000

Cursor position remains stable even when commas are inserted.

Additional Information

Contributions

This package was created to solve production currency-input challenges in the Oinkoin project.

Contributions, suggestions, and bug reports are welcome.

You can contribute by:

  • Opening issues
  • Submitting pull requests
  • Improving documentation

License

MIT License — free for personal and commercial use.

⭐ If you find this package useful, consider starring the repository!

Libraries

smart_input_formatters