const FloatingActionButton({Key key, @required Widget child, String tooltip, Color backgroundColor, Object heroTag, int elevation: 6, int highlightElevation: 12, @required VoidCallback onPressed, bool mini: false })

Creates a floating action button.

Most commonly used in the floatingActionButton field.

Source 

const FloatingActionButton({
  Key key,
  @required this.child,
  this.tooltip,
  this.backgroundColor,
  this.heroTag,
  this.elevation: 6,
  this.highlightElevation: 12,
  @required this.onPressed,
  this.mini: false
}) : super(key: key);