https://twitter.com/andrewpmoore/status/1653024430996574209

auto_fill_text.dart

import 'package:app/extensions.dart';
import 'package:flutter/material.dart';

class AutoFillText extends StatelessWidget {
  const AutoFillText(
    this.text, {
    super.key,
    this.textStyle,
    this.minFontSize = 18,
  });

  final String text;

  final double minFontSize;

  final TextStyle? textStyle;

  @override
  Widget build(BuildContext context) {
    var style = DefaultTextStyle.of(context).style;
    if (textStyle != null) {
      style = style.merge(textStyle);
    }

    return LayoutBuilder(
      builder: (context, constraints) {
        const step = 1.0;
        final frameSize = constraints.bounded;
        final maxFontSize = style.fontSize!;

        var textSize = style.size(text, maxWidth: frameSize.width);
        var fontSize = maxFontSize;

        while (!frameSize.containsSize(textSize) &&
            fontSize <= maxFontSize &&
            fontSize >= minFontSize) {
          textSize = style
              .copyWith(fontSize: fontSize)
              .size(text, maxWidth: frameSize.width);
          fontSize -= step;
        }

        return Text(
          text,
          style: style.copyWith(fontSize: fontSize),
          overflow: TextOverflow.fade,
        );
      },
    );
  }
}

extension BoxConstraintsExtensions on BoxConstraints {
  bool get isBounded => hasBoundedHeight && hasBoundedWidth;

  Size get bounded {
    assert(isBounded);
    return biggest;
  }
}

extension SizeExtensions on Size {
  bool containsSize(Size other) {
    return width >= other.width && height >= other.height;
  }
}

extension TextStyleExtensions on TextStyle {
  Size size(String text, {double maxWidth = double.infinity}) {
    final textSpan = TextSpan(text: text, style: this);
    final textPainter = TextPainter(
      text: textSpan,
      textDirection: TextDirection.ltr,
      maxLines: null,
      textAlign: TextAlign.left,
    );
    textPainter.layout(maxWidth: maxWidth);
    return textPainter.size;
  }
}

Simple text that fills the container. Not sure why this hasn't been solved in four years. And if it has, why I couldn't find it.

foo.mp4

that's a great way of handling text! just wondering with your extensions, for bounded are you getting the max height and width of the container like this?

final frameSize = Size(constraints.maxWidth, constraints.maxHeight);

Thanks for the reminder, I updated the code to include bounded and other extensions