attemptExpand method

bool attemptExpand(int index, int direction, double delta)

Implementation

bool attemptExpand(int index, int direction, double delta) {
  final item = items[index];
  double currentSize = item.newValue; // check
  double minSize = item.min;
  double maxSize = item.max;
  double newSize = currentSize + delta;
  double minOverflow = newSize - minSize;
  double maxOverflow = newSize - maxSize;

  if (minOverflow < 0 && delta < 0) {
    delta = delta - minOverflow;
  }

  if (maxOverflow > 0 && delta > 0) {
    delta = delta - maxOverflow;
  }

  if (delta == 0) {
    return false;
  }

  if (index == 0) {
    direction = 1;
  } else if (index == items.length - 1) {
    direction = -1;
  }
  if (direction < 0) {
    var borrowed = _borrowSize(index - 1, -delta, 0, -1);
    if (borrowed.givenSize != -delta) {
      reset();
      return false;
    }
    item._newValue = (item.newValue + delta).clamp(minSize, maxSize);
    // check
    return true;
  } else if (direction > 0) {
    var borrowed = _borrowSize(index + 1, -delta, items.length - 1, 1);
    if (borrowed.givenSize != -delta) {
      reset();
      return false;
    }
    item._newValue = (item.newValue + delta).clamp(minSize, maxSize);
    // check
    return true;
  } else if (direction == 0) {
    double halfDelta = delta / 2;
    var borrowedLeft = _borrowSize(index - 1, -halfDelta, 0, -1);
    var borrowedRight =
        _borrowSize(index + 1, -halfDelta, items.length - 1, 1);
    if (borrowedLeft.givenSize != -halfDelta ||
        borrowedRight.givenSize != -halfDelta) {
      reset();
      return false;
    }
    item._newValue = (item.newValue + delta).clamp(minSize, maxSize);
    // check
    return true;
  }
  return false;
}