expand method
Bring the panel to PanelState.expanded.
Returned future is completed when the panel is expanded.
(Animates to PanelSize.expandedHeight).
Implementation
Future<Null> expand() async => controlling
? _setPanelPosition(panel!,
duration: currentState == PanelState.collapsed
? _durationExpanded
: currentState == PanelState.closed
? panel!.widget.duration
: _getDuration(
from: currentPosition,
to: panel!._metadata.expandedHeight),
to: panel!._metadata.expandedHeight)
: Future.error('Missing Controller');