fit_text

Text that shrinks to fit its box, correctly. Works inside Expanded, Row, IntrinsicHeight and unbounded constraints, where LayoutBuilder-based auto-sizing gives up.

fit_text

The same sentence in a narrowing box

Text that shrinks to fit its box — including in the places auto-sizing usually breaks.

FitText('A headline that must never wrap', maxLines: 1, minFontSize: 12)

The problem this fixes

Flutter has no built-in way to make text fit: Text overflows or clips. The established workaround measures inside a LayoutBuilder, and that works right up until the widget lands somewhere Flutter needs an intrinsic size first:

LayoutBuilder does not support returning intrinsic dimensions.
  at _RenderLayoutBuilder.computeMaxIntrinsicHeight

That is a hard framework limitation, not a bug someone forgot to fix. It rules LayoutBuilder-based auto-sizing out of:

IntrinsicHeight and IntrinsicWidth
Table cells — columns size with intrinsics by default
Baseline-aligned rows

FitText does the fitting inside its own RenderBox, during layout. Intrinsics are answered honestly, so it works in all of those. There is a test in the suite that pins the LayoutBuilder failure alongside FitText succeeding in the same tree, so the difference is verified rather than asserted.

Install

dependencies:
  fit_text: ^0.2.0

Usage

// Shrink to fit one line, never below 12.
FitText('Long product name', maxLines: 1, minFontSize: 12);

// Grow to fill, but stay on your type scale.
FitText('42', presetFontSizes: [16, 24, 32, 48, 64]);

// Rich text — nested sizes scale proportionally.
FitText.rich(
  TextSpan(text: 'Total ', children: [
    TextSpan(text: '£42', style: TextStyle(fontWeight: FontWeight.bold)),
  ]),
  maxLines: 1,
);

Both constructors are const, like Text.

Matching sizes across widgets

Independently fitted labels land on different sizes, which looks wrong across a row of buttons. A group makes them agree on the smallest size any member needed, so they match and all of them still fit.

final labels = FitTextGroup();   // hold this in state

Row(children: [
  Expanded(child: FitText('Save', group: labels, maxLines: 1)),
  Expanded(child: FitText('Discard changes', group: labels, maxLines: 1)),
]);

Members find their own size first and agree on the next frame, so a group settles one frame after its contents change.

Options


`minFontSize`	Floor. Below this the text overflows instead of shrinking further.
`maxFontSize`	Ceiling. Defaults to the inherited style's size, so text shrinks but never grows unless you ask.
`stepGranularity`	Increment between candidate sizes.
`presetFontSizes`	An explicit scale, instead of a stepped range.
`group`	Share a size with other members.

Everything Text takes — textAlign, maxLines, softWrap, overflow, strutStyle, textScaler, locale, textWidthBasis — behaves the same way.

Cost

Finding the size is a bisection, not a scan: about log2((max - min) / step) text layouts, so six or so for the defaults. It re-runs only when the text, style, or constraints change, and RenderFitText.fittedFontSize exposes what it chose if you need to react to it.

Coming from auto_size_text

The API is deliberately close, so most call sites change only the widget name.

auto_size_text	fit_text
`AutoSizeText(...)`	`FitText(...)`
`AutoSizeText.rich(...)`	`FitText.rich(...)`
`AutoSizeGroup()`	`FitTextGroup()`
`group: myGroup`	`group: myGroup`

| overflowReplacement: | overflowReplacement: |

| wrapWords: false | wrapWords: false |

Neither package supports text selection.

One difference worth knowing: overflowReplacement stays mounted whether or not it is used, collapsed to zero size — the same trade IndexedStack makes. That is what lets the swap happen inside a single layout pass with no frame of overflowing text, but it means an expensive replacement widget is built even when it never shows. Keep it cheap.

License

fit_text on pub.dev