updateDrag method
Implementation
void updateDrag(DragUpdateDetails details) {
if ((pointers == 1 && !fromTwoFinger) || updated || !oneFingerScrolling) {
diff = positionY - details.globalPosition.dy;
double newHeight = currentHeight + diff;
if (newHeight > maxHeight) {
newHeight = maxHeight;
} else if (newHeight < minHeight) {
newHeight = minHeight;
}
currentHeight = newHeight;
positionY = details.globalPosition.dy;
updated = true;
update();
}
}