semanticFormatterCallback property

SemanticFormatterCallback? semanticFormatterCallback

The callback used to create a semantic value from a slider value.

Defaults to formatting values as a percentage.

This is used by accessibility frameworks like TalkBack on Android to inform users what the currently selected value is with more context.

In the example below, a slider for currency values is configured to announce a value with a currency label.

Slider(
  value: _dollars.toDouble(),
  min: 20.0,
  max: 330.0,
  label: '$_dollars dollars',
  onChanged: (double newValue) {
    setState(() {
      _dollars = newValue.round();
    });
  },
  semanticFormatterCallback: (double newValue) {
    return '${newValue.round()} dollars';
  }
 )

Ignored if this slider is created with Slider.adaptive

Implementation

// TODO(framework): Add unit tests to this code snippet.
// https://github.com/flutter/flutter/issues/188530
///
/// In the example below, a slider for currency values is configured to
/// announce a value with a currency label.
///
/// ```dart
/// Slider(
///   value: _dollars.toDouble(),
///   min: 20.0,
///   max: 330.0,
///   label: '$_dollars dollars',
///   onChanged: (double newValue) {
///     setState(() {
///       _dollars = newValue.round();
///     });
///   },
///   semanticFormatterCallback: (double newValue) {
///     return '${newValue.round()} dollars';
///   }
///  )
/// ```
///
/// </callout-box>
///
/// Ignored if this slider is created with [Slider.adaptive]
final SemanticFormatterCallback? semanticFormatterCallback;