Flutter Slider – onChangeStart

Flutter Slider onChangeStart

onChangeStart property of Slider takes a function, and is called only when the slider value starts changing.

Sample Code

The callback function receives the initial value of the slider when the change has started.

Slider(
  onChangeStart: (double value) {
    //some code
  },
),

Example

Flutter Application with a Slider widget.

We display the value received by onChangeStart of slider in a Text widget.

main.dart

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

/// main application widget
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Application';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatefulWidget(),
      ),
    );
  }
}

/// stateful widget that the main application instantiates
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

/// private State class that goes with MyStatefulWidget
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  double _currentSliderValue = 40;
  double _startSliderValue = -1;
  double _endSliderValue = -1;
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: <Widget>[
          Slider(
            value: _currentSliderValue,
            min: 0,
            max: 100,
            divisions: 100,
            label: _currentSliderValue.round().toString(),
            onChanged: (double value) {
              setState(() {
                _currentSliderValue = value;
              });
            },
            onChangeStart: (double value) {
              setState(() {
                _startSliderValue = value;
              });
            },
            onChangeEnd: (double value) {
              setState(() {
                _endSliderValue = value;
              });
            },
          ),
          Text('Starting Value : ' + _startSliderValue.round().toString()),
          Text('Current Slider Value : ' + _currentSliderValue.round().toString()),
          Text('Stop Value : ' + _endSliderValue.round().toString()),
        ],
      ),
    );
  }
}

Video