Auto Size TextField

✍️ Flutter TextField widget that automatically resizes text field to fit perfectly within its bounds.

📢 Announcement:

🚒 ️️IMPORTANT v2.0.0 is for Flutter v3. For Flutter v2 and below, please continue to use v1.0.1

Note: Kudos to @leisim! This work is inspired by his awesome lib Auto Size Text. Please check it out if you want to auto size the Flutter Text widget content.

Show some ❤️ and star the repo to support the project

TODO

• Update README.md to show examples of more use cases
• Update the example to support Flutter v3

Contents

• Usage
  • maxLines
  • minFontSize & maxFontSize
  • stepGranularity
  • presetFontSizes
  • overflowReplacement
• Parameters
• Performance
• Troubleshooting
  • Missing bounds
  • MinFontSize too large

Usage

AutoSizeTextField behaves exactly like a TextField. The only difference is that it resizes text to fit within its bounds.

AutoSizeTextField(
  controller: _textEditingController,
  style: TextStyle(fontSize: 20),
  maxLines: 2,
)

Note: AutoSizeTextField needs bounded constraints to resize the text. More info here.

fullwidth (default value: true)

The fullwidth parameter extends the width of TextField to its parent's BoxContraints to occupy full width.

Set to false to let the width TextField determined by the width of the text.

maxLines

The maxLines parameter works like you are used to with the Text widget. If there is no maxLines parameter specified, the AutoSizeTextField only fits the text according to the available width and height.

AutoSizeTextField(
  controller: _textEditingController,
  style: TextStyle(fontSize: 30),
  maxLines: null,
  decoration: InputDecoration(
    border: InputBorder.none,
    isDense: true,
    contentPadding: const EdgeInsets.all(20)
  ),
)

minFontSize & maxFontSize

The AutoSizeTextField starts with TextStyle.fontSize. It measures the resulting text and rescales it to fit within its bonds. You can however set the allowed range of the resulting font size.

With minFontSize you can specify the smallest possible font size. If the text still doesn't fit, it will be handled according to overflow. The default minFontSize is 12.

maxFontSize sets the largest possible font size. This is useful if the TextStyle inherits the font size and you want to constrain it.

AutoSizeTextField(
  controller: _textEditingController,
  style: TextStyle(fontSize: 30),
  minFontSize: 18,
  maxLines: 4,
  overflow: TextOverflow.ellipsis,
)

stepGranularity

The AutoSizeTextField will try each font size, starting with TextStyle.fontSize until the text fits within its bounds.
stepGranularity specifies how much the font size is decreased each step. Usually, this value should not be below 1 for best performance.

AutoSizeTextField(
  controller: _textEditingController,
  style: TextStyle(fontSize: 40),
  minFontSize: 10,
  stepGranularity: 10,
  maxLines: 4,
  overflow: TextOverflow.ellipsis,
)

presetFontSizes

If you want to allow only specific font sizes, you can set them with presetFontSizes. If presetFontSizes is set, minFontSize, maxFontSize and stepGranularity will be ignored.

AutoSizeTextField(
  controller: _textEditingController,
  presetFontSizes: [40, 20, 14],
  maxLines: 4,
)

overflowReplacement

If the text is overflowing and does not fit its bounds, this widget is displayed instead. This can be useful to prevent text being too small to read.

AutoSizeTextField(
  maxLines: 1,
  controller: _textEditingController
)

Parameters

Parameter	Description
key*	Controls how one widget replaces another widget in the tree.
textKey	Sets the key for the resulting Text widget
style*	If non-null, the style to use for this text
fullwidth	Default: true, It extends the width of TextField to its parent's BoxContraints to occupy full width. Set to false to let the width TextField determined by the width of the text.
minFontSize	The minimum text size constraint to be used when auto-sizing text. Is being ignored if presetFontSizes is set.
maxFontSize	The maximum text size constraint to be used when auto-sizing text. Is being ignored if presetFontSizes is set.
stepGranularity	The step size in which the font size is being adapted to constraints.
presetFontSizes	Predefines all the possible font sizes. Important: presetFontSizes have to be in descending order.
locale*	Used to select a font when the same Unicode character can be rendered differently, depending on the locale.
wrapWords	Whether words which don't fit in one line should be wrapped. Defaults to true to behave like Text.
overflowReplacement	If the text is overflowing and does not fit its bounds, this widget is displayed instead.
maxLines	An optional maximum number of lines for the text to span.
minWidth	An optional min width for input field. Only set it when fullwidth = false

• Parameters marked with * behave exactly the same as in TextField.
• The unlisted parameters behave exactly the same as TextField.

Performance

AutoSizeTextField is really fast. In fact, you can replace all your TextField widgets with AutoSizeTextField.
Nevertheless you should not use an unreasonable high fontSize in your TextStyle. E.g. don't set the fontSize to 1000 if you know, that the text will never be larger than 30.

If your font size has a very large range, consider increasing stepGranularity.

Troubleshooting

Missing bounds

If AutoSizeTextField overflows or does not resize the text, you should check if it has constrained width and height.

Wrong code:

Row(
  children: <Widget>[
    AutoSizeTextField(
      controller: _textEditingController,
      maxLines: 1,
    ),
  ],
)

Because Row and other widgets like Container, Column or ListView do not constrain their children, the text will overflow.
You can fix this by constraining the AutoSizeTextField. Wrap it with Expanded in case of Row and Column or use a SizedBox or another widget with fixed width (and height).

Correct code:

Row(
  children: <Widget>[
    Expanded( // Constrains AutoSizeTextField to the width of the Row
      child: AutoSizeTextField(
        controller: _textEditingController,
        maxLines: 1,
      )
    ),
  ],
)
}

MinFontSize too large

AutoSizeTextField does not resize text below the minFontSize which defaults to 12.:

MIT License

Copyright (c) 2020 Zhuoran LI

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the 'Software'), to deal
in the Software without restriction, including without limitation the rights
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copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.