fabrizzioRP

Route navigateScreenFadeIn( BuildContext context , Widget screen ) => 
  PageRouteBuilder(
    pageBuilder : ( _ , __ , ___) => screen,
    transitionDuration : const Duration(milliseconds: 300),
    transitionBuilder : ( context , animation , _, child) => 
      FadeTransition(
        opacity : Tween<double>(begin : 0.0 , end : 1.0).animate( CurvedAnimation( parent : animation , curve : Curves.easeOut ) ),
        child : child
      ),
  );

fabrizzioRP

final Widget rectangle = Container(
  width  : 150,
  height : 70,
  color  : Colors.red,
  child  : Center( 
     child :  Text('Rectangle'),
  ),
);