How to debounce Textfield onChange in Dart?

Implementation

Import dependencies:

import 'dart:async';

In your widget state declare a timer:

Timer? _debounce;

Add a listener method:

_onSearchChanged(String query) {
    if (_debounce?.isActive ?? false) _debounce.cancel();
    _debounce = Timer(const Duration(milliseconds: 500), () {
        // do something with query
    });
    }

Don't forget to clean up:

@override
void dispose() {
    _debounce?.cancel();
    super.dispose();
}

Usage

In your build tree hook the onChanged event:

child: TextField(
        onChanged: _onSearchChanged,
        // ...
    )

Here is my solution

 subject = new PublishSubject<String>();
      subject.stream
          .debounceTime(Duration(milliseconds: 300))
          .where((value) => value.isNotEmpty && value.toString().length > 1)
          .distinct()
          .listen(_search);

Using BehaviorSubject from rxdart lib is a good solution. It ignores changes that happen within X seconds of the previous.

final searchOnChange = new BehaviorSubject<String>();
...
TextField(onChanged: _search)
...

void _search(String queryString) {
  searchOnChange.add(queryString);
}   

void initState() {    
  searchOnChange.debounceTime(Duration(seconds: 1)).listen((queryString) { 
  >> request data from your API
  });
}

You can make Debouncer class using Timer

import 'package:flutter/foundation.dart';
import 'dart:async';

class Debouncer {
  final int milliseconds;
  Timer? _timer;

  Debouncer({required this.milliseconds});

  run(VoidCallback action) {
    _timer?.cancel();
    _timer = Timer(Duration(milliseconds: milliseconds), action);
  }
}

Declare it

final _debouncer = Debouncer(milliseconds: 500);

and trigger it

onTextChange(String text) {
  _debouncer.run(() => print(text));
}