measure_size

A Flutter package for efficiently measuring widget sizes and building size-aware, adaptive layouts with minimal overhead.

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Measuring text and drawing an overlay with matching size

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	MeasureSize	MeasureSizeBuilder
Purpose	Monitor size changes	Prototype-driven layout
Callback timing	Post-frame	During layout (invokeLayoutCallback)
Measurements	Single widget	Multiple prototypes
Use case	Reactive to size changes	Proactive layout decisions
Complexity	Simple	Advanced
Performance	Good	Excellent (single pass)
PreferredSizeWidget limitation	Does not work	First frame problematic

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import 'package:measure_size/measure_size.dart';

Widget child = Text('Lorem ipsum dolor sit amet');

MeasureSize(
    onChange: (Size newSize) {
        /// [newSize] will be the displayed size of [Widget child]
    },
    child: child,
);

MeasureSizeBuilder<String>(
    prototypeConstraints: (constraints) => BoxConstraints(
      minWidth: 0,
      maxWidth: constraints.maxWidth,
      minHeight: 0,
      maxHeight: double.infinity,
    ),
    prototypes: [
      PrototypeId(
        id: 'lorem',
        child: child,
      ),
    ],
    builder: (context, sizes) {
      // [sizes['lorem']] will be the layed out size of [Widget child]
      return child;
    }
);

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MeasureSize

Required

• Widget child - This widget will be displayed and and measured.

Optional

• void onChange(Size newSize) - A callback that is fired exactly once after the first frame of the child widget is rendered.

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MeasureSizeBuilder<T>

Required

• List<PrototypeId<T>> prototypes - Wrap widgets you'd like to measure with PrototypeId and provide a unique identifier for each widget.
• PrototypeWidgetBuilder<T> builder - A builder function that contains the sizes of all prototypes.
• PrototypeConstraintCalculator prototypeConstraints - Constraints to be assigned to each prototype widget.

Example

A demonstration can be found in the example directory. To run the example:

flutter run example/main.dart

Credits

• Thanks to @jacksonrl for the prototype solution
• Thanks to Gene Bo and Dev Aggarwal for this code in a stackoverflow answer: https://stackoverflow.com/a/60868972