How to get current index of listview in flutter?

Question

I have list include 5 items, i want get current index when scroll. I was use scrollcontroller and addListener it. But when use this way it will lag when scroll. I want instead it with another way. How to do it? Thank for everyone!

I was try with similar code is:

void _scrollListener() {
    int firstVisibleIndex = _scrollLayoutController.hasClients
        ? (_scrollLayoutController.offset / _itemHeight).floor()
        : 0;

    setState(() {
      _currentIndex = firstVisibleIndex;
    });
  }

Answer 1

I was solve issue when use timer, this helps reduce the number of index calculations and prevents unnecessary updates during continuous scrolling, leading to better performance.

class Debouncer {
  final Duration delay;
  Timer? _timer;

  Debouncer(this.delay);

  void call(VoidCallback action) {
    _timer?.cancel(); // Cancel any previous timer that hasn't executed yet
    _timer = Timer(delay, action); // Create a new timer to execute the action after the specified delay
  }

  void cancel() {
    _timer?.cancel();
  }
}

class Throttle {
  final Duration delay;
  Timer? _timer;
  bool _canCall = true;

  Throttle(this.delay);

  void call(VoidCallback action) {
    if (_canCall) {
      _canCall = false; // Mark that a function call is in progress
      action(); // Execute the action
      _timer = Timer(delay, () {
        _canCall = true; // Allow the next function call after the specified delay
      });
    }
  }

  void cancel() {
    _timer?.cancel(); 
    _canCall = true;
  }
}
void _scrollListener() {
    _debouncer(() {
      int firstVisibleIndex = _scrollLayoutController.hasClients
          ? (_scrollLayoutController.offset / _itemHeight).floor()
          : 0;

      setState(() {
        _currentIndex = firstVisibleIndex;
      });
    });
  }