text_autosize 0.2.0

Automatically resize text to fit its bounds: shrink the font until the text fits the available width, height and maxLines. TextScaler-aware, API-compatible with auto_size_text.

text_autosize

A Flutter widget that automatically resizes text to fit within its bounds.

The API follows the auto_size_text package by Simon Leier, so existing code migrates by changing the import. On top of the familiar API, this package is built against current Flutter releases and handles TextScaler correctly, including nonlinear system font scaling.

Demo

Features

• Shrinks text until it fits the available width, height and maxLines.
• minFontSize, maxFontSize and stepGranularity control the search range.
• presetFontSizes restricts the text to a fixed list of sizes.
• AutoSizeGroup keeps several texts at the same size.
• AutoSizeText.rich resizes a whole TextSpan tree proportionally.
• overflowReplacement swaps in another widget when nothing fits.
• textScaler aware: the fitted size accounts for the user's font scale.
• Works inside SelectionArea, since it builds a regular Text widget.

Usage

Requires Flutter 3.32 or later.

import 'package:text_autosize/text_autosize.dart';

AutoSizeText(
  'The text to display',
  style: TextStyle(fontSize: 20),
  maxLines: 2,
)

The widget behaves like Text, except that it lowers the font size until the text fits the incoming constraints. It needs bounded constraints to resize against, for example from a SizedBox or an Expanded.

maxLines and minFontSize

AutoSizeText(
  'A single line that shrinks down to 10 before it ellipsizes',
  style: TextStyle(fontSize: 30),
  maxLines: 1,
  minFontSize: 10,
  overflow: TextOverflow.ellipsis,
)

Preset font sizes

If only some sizes are allowed, pass them in descending order. The first size that fits is used:

AutoSizeText(
  'One of three sizes',
  presetFontSizes: [40, 20, 14],
  maxLines: 1,
)

Synchronizing several texts

Give all texts the same AutoSizeGroup. Every member renders at the size of the most constrained one:

final group = AutoSizeGroup();

AutoSizeText('Label one', group: group, maxLines: 1);
AutoSizeText('A much longer label two', group: group, maxLines: 1);

Rich text

AutoSizeText.rich(
  TextSpan(
    text: 'Mixed ',
    children: [
      TextSpan(text: 'sizes', style: TextStyle(fontSize: 40)),
    ],
  ),
  style: TextStyle(fontSize: 20),
  maxLines: 1,
)

All font sizes in the span tree are scaled by the same factor, so the proportions of the spans are preserved.

Overflow replacement

AutoSizeText(
  'A text that might not fit at minFontSize',
  minFontSize: 16,
  overflowReplacement: Text('Not enough room'),
)

Migration from auto_size_text

1. Replace the dependency:

   flutter pub remove auto_size_text
   flutter pub add text_autosize
   

2. Replace the import. The class names AutoSizeText and AutoSizeGroup are unchanged:

   import 'package:text_autosize/text_autosize.dart';
   

3. Optionally move textScaleFactor to textScaler. This step is no longer required to compile: textScaleFactor still works and is treated as TextScaler.linear(factor). It is deprecated and will be removed in a future release, so prefer textScaler:

   // still compiles, deprecated
   AutoSizeText('Hello', textScaleFactor: 1.5)
   // preferred
   AutoSizeText('Hello', textScaler: TextScaler.linear(1.5))
   

   Setting both textScaler and textScaleFactor on the same widget is not allowed and asserts in debug builds.

Intentional behavior differences from auto_size_text 3.0.0:

• The built Text carries the logical font size plus a TextScaler, instead of a pre-scaled font size with scaling disabled. The rendered pixels are identical; only the internal representation differs. Migrated tests that look up the inner Text through textKey and assert on style.fontSize see the logical value now.
• With a linear scaler, minFontSize, maxFontSize and presetFontSizes produce the same rendered size as the original package. The behavior only differs under a nonlinear scaler (for example Android 14 system font scaling), where the fitted size is computed with the actual scaler instead of a single factor.
• Rich text is measured with the fully resolved style, exactly as Text.rich renders it. The original measured the span's own style only, which could mismeasure spans that inherit their size from DefaultTextStyle.
• Measurement resolves textAlign and textDirection the same way the rendered Text does, instead of assuming left-aligned, left-to-right text.
• An AutoSizeGroup synchronizes the logical font size of its members. Each member still applies its own TextScaler when rendering.
• presetFontSizes must be in descending order; this is now checked with an assert instead of being silently required.
• textWidthBasis, textHeightBehavior and selectionColor are passed through to the built Text.

How it works

The widget measures the text with a TextPainter against the incoming constraints. If the preferred font size does not fit, a binary search runs over the candidate sizes between minFontSize and the preferred size in steps of stepGranularity, or over presetFontSizes if given. A build therefore performs O(log n) text layouts for n candidate sizes, and a single TextPainter instance is reused for all measurements.

Limitations

• The widget only shrinks text below its preferred size. It does not grow text to fill extra space, except through presetFontSizes.
• Resizing needs a bounded constraint. In an unbounded context, such as the scroll direction of a ListView or inside an UnconstrainedBox, the text keeps its preferred size. This is safe but performs no resizing on that axis.
• The widget is built around a LayoutBuilder, so it cannot be used where intrinsic dimensions are required, for example inside IntrinsicWidth or IntrinsicHeight.
• strutStyle is passed through as given and is not resized with the text. A strut with a fixed font size puts a floor under the line height.
• softWrap: false affects rendering but not measurement, so text that is fitted with wrapping in mind can still overflow horizontally when soft wrapping is disabled. This matches auto_size_text.
• With wrapWords: false, the longest-word check measures the words with the base style only. Per-span font sizes of rich text are not considered in that check. This also matches auto_size_text.

Credits

The API follows the auto_size_text package by Simon Leier.

License

MIT. See LICENSE.