smart_input_formatters 0.0.2

A set of high-performance Flutter TextInputFormatters for currency, math expressions, and auto-decimal shifting with cursor stability.

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.

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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

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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';

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Usage

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

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Simple Amount (No Math)

If you want a clean, digits-only field for simple price entry:

TextFormField(
  inputFormatters: SmartAmountFormatter(
  decimalSep: '.',
  groupSep: ',',
  allowExpression: false, // Blocks all math operators
).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

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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

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How It Works (Formatting Pipeline)

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

0. Filtering Selection

The first line of defense. It immediately blocks any character that isn't a digit, a separator, or a math operator (if allowExpression is true).

Benefit: Prevents letters, emojis, and invalid symbols from ever entering the field.

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1. CalculatorNormalizer

Standardizes operators and separators.

Examples:

• x → *
• . ↔ , depending on locale

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2. LeadingZeroIntegerTrimmer

Removes redundant leading zeros.

Examples:

• 000123 → 123
• 0000 → 0

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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

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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.

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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

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License

MIT License — free for personal and commercial use.

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