Flexible({Key key, int flex: 1, FlexFit fit: FlexFit.tight, @required Widget child })

Creates a widget that controls how a child of a Row, Column, or Flex flexes.

Source 

Flexible({
  Key key,
  this.flex: 1,
  this.fit: FlexFit.tight,
  @required Widget child,
}) : super(key: key, child: child);