My slider have value well changed , but cant move it , or cant display changes

Question

  @override
  Widget build(BuildContext context) {
    double currentSliderValue = 100.0;
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Slider(
        value: currentSliderValue,
        onChanged: (double value) {
          setState(() {
            currentSliderValue = value;
          });
        },
        label: '$currentSliderValue',
      ),
      ),
    );
  }
}

I tyied to make a slider , its very similir as other example, its value could be changed, but didnt move at all

Answer 1

the problem is that you initialize the value inside the build method, which is called every time the widget is rendered, as with setState.

Just change to this

double currentSliderValue = 100.0;     
@override
  Widget build(BuildContext context) {

Answer 2

The slider holds values from 0 to 1. And your initial value is 100. Which is giving you the error.

Slider(
        value: currentSliderValue,
.....
)

Here is your working code.

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: HomePage(title: "Home Page"),
    ),
  );
}

class HomePage extends StatefulWidget {
  HomePage({super.key, required this.title});
  String title;

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  double currentSliderValue = 1;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Slider(
        value: currentSliderValue,
        onChanged: (double value) {
          setState(() {
            currentSliderValue = value;
          });
        },
        label: '$currentSliderValue',
      ),
    );
  }
}