openDrawer method

void openDrawer ()

Opens the Drawer (if any).

If the scaffold has a non-null Scaffold.drawer, this function will cause the drawer to begin its entrance animation.

Normally this is not needed since the Scaffold automatically shows an appropriate IconButton, and handles the edge-swipe gesture, to show the drawer.

To close the drawer once it is open, use Navigator.pop.

See Scaffold.of for information about how to obtain the ScaffoldState.

Implementation 

void openDrawer() {
  if (_endDrawerKey.currentState != null && _endDrawerOpened)
    _endDrawerKey.currentState.close();
  _drawerKey.currentState?.open();
}