ensureVisible method

Future<void> ensureVisible({ Duration duration = const Duration(milliseconds: 100), Curve curve = Curves.ease, double? preciseAlignment, })

If you omit preciseAlignment or pass null, the widget will just be scrolled into view, i.e. the scroll view will be scrolled just enough for the widget to appear at the bottom or top of the viewport. This will take a duration specified by duration and follow a curve specified by curve. The duration defaults to 100 milliseconds and the curve to Curves.ease.

If you want to have the widget scrolled to a specific alignment, you need to set preciseAlignment. This value represents to what extent your widget should be scrolled into the viewport:

• preciseAlignment: 0 will scroll your widget to the start of your viewport.
• preciseAlignment: 0.5 will scroll your widget to the center of your viewport.
• preciseAlignment: 1 will scroll your widget to the end of your viewport.
• preciseAlignment: null or just omitting it will let the package handle the alignment and will just scroll your widget into view.

Implementation

Future<void> ensureVisible({
  Duration duration = const Duration(milliseconds: 100),
  Curve curve = Curves.ease,
  double? preciseAlignment,
}) async {
  assert(
      preciseAlignment == null ||
          (preciseAlignment > 0 && preciseAlignment < 1),
      'The alignment needs to be null or between 0 and 1.');

  final renderObject = context.findRenderObject();
  final viewport = RenderAbstractViewport.of(renderObject)!;

  final scrollableState = Scrollable.of(context)!;

  final position = scrollableState.position;
  double alignment;

  if (preciseAlignment != null) {
    alignment = preciseAlignment;
    // Only if the precise alignment exactly matches the current position no scrolling is necessary.
    if (position.pixels ==
        viewport.getOffsetToReveal(renderObject!, preciseAlignment).offset)
      return;
  } else if (position.pixels >
      viewport.getOffsetToReveal(renderObject!, 0).offset) {
    // Move down to the top of the viewport
    alignment = 0;
  } else if (position.pixels <
      viewport.getOffsetToReveal(renderObject, 1).offset) {
    // Move up to the bottom of the viewport
    alignment = 1;
  } else {
    // No scrolling is necessary to reveal the child
    return;
  }
  return await position.ensureVisible(
    renderObject,
    alignment: alignment,
    duration: duration,
    curve: curve,
  );
}