showHandles method
Builds the handles by inserting them into the context's overlay.
Implementation
void showHandles() {
if (_handles != null) {
return;
}
_handles = (
start: OverlayEntry(builder: _buildStartHandle),
end: OverlayEntry(builder: _buildEndHandle),
);
Overlay.of(context, rootOverlay: true, debugRequiredFor: debugRequiredFor)
.insertAll(<OverlayEntry>[_handles!.start, _handles!.end]);
}