Flutter scrollcontroller listener

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Flutter ScrollController Listener

In Flutter, ScrollController is a widget that controls the position of a Scrollable widget, such as ListView, GridView, or SingleChildScrollView. The ScrollController allows you to listen to scroll events and perform certain actions based on the scroll position or offset.

To listen to scroll events using ScrollController, you need to follow these steps:

  1. Create an instance of ScrollController by calling its constructor.
  2. Assign the ScrollController to the scrollable widget’s controller property.
  3. Implement a listener function that will be called whenever a scroll event occurs.
  4. Register the listener function using the ScrollController’s addListener() method.
  5. Perform desired actions based on the scroll position or offset inside the listener function.

Here’s an example of how to use ScrollController listener: 

    
import 'package:flutter/material.dart';

class MyScrollableWidget extends StatefulWidget {
  @override
  _MyScrollableWidgetState createState() => _MyScrollableWidgetState();
}

class _MyScrollableWidgetState extends State {
  ScrollController _scrollController;

  @override
  void initState() {
    _scrollController = ScrollController();
    _scrollController.addListener(_scrollListener);
    super.initState();
  }

  @override
  void dispose() {
    _scrollController.removeListener(_scrollListener);
    _scrollController.dispose();
    super.dispose();
  }

  void _scrollListener() {
    if (_scrollController.position.pixels == _scrollController.position.maxScrollExtent) {
      // Bottom of the scrollable content reached
      print("Scrolled to bottom!");
    }
  }

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      controller: _scrollController,
      itemCount: 100,
      itemBuilder: (context, index) {
        return ListTile(
          title: Text("Item $index"),
        );
      },
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      appBar: AppBar(
        title: Text("ScrollController Listener"),
      ),
      body: MyScrollableWidget(),
    ),
  ));
}

In the above example, a ScrollController is created and assigned to the ListView’s controller property. The listener function “_scrollListener” is registered using the addListener() method. In the listener function, it checks if the scroll position is at the bottom (maxScrollExtent) and prints a message if so.

The ScrollController is properly disposed of in the dispose() method to avoid memory leaks.

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