scroll to widget method

scroll_to_widget_function.dart

void _scrollToWidget() async {
  // find the index of fruit to scroll to in fruits
  // let's scroll to Mandarina
  final index = fruits.indexOf('Mandarina');
  // get global key of Mandarina
  final key = _fruitKeys[index];
  // find the render box of Mandarina
  var box = key.currentContext?.findRenderObject();

  // if box is not in the view port, scroll to it
  if (box == null) {
    // speed to scroll to Mandarina
    double scrollSpeed;
    // find the key of the render box which is currently in view
    var currentKeyIndex = _fruitKeys.indexWhere(
        (element) => element.currentContext?.findRenderObject() != null);
    // if currently visible fruit is before fruit which we need to scroll to,
    // then speed should be negative because we want to scroll up otherwise positive i.e sroll down
    scrollSpeed = currentKeyIndex > index ? 100 : -100;

    // scroll until render object is found
    while (box == null) {
      var offset = _scrollController.offset - scrollSpeed;
      await _scrollController.animateTo(
        offset,
        duration: const Duration(milliseconds: 1),
        curve: Curves.easeInOut,
      );
      box = key.currentContext?.findRenderObject();
    }
  }

  _scrollController.position.ensureVisible(
    box,
    // How far into view the item should be scrolled (between 0 and 1)
    // with 1 being the bottom of the view and 0 being the top.
    alignment: 0.2,
    duration: const Duration(milliseconds: 200),
  );
}