【Flutter】LayoutBuilder作为child获取父

LayoutBuilder(
    builder: (context, constraints){
      /// constraints 

      /// The maximum width that satisfies the constraints.
      ///
      /// Might be [double.infinity].
      final double maxWidth;

      /// The maximum height that satisfies the constraints.
      ///
      /// Might be [double.infinity].
      final double maxHeight;
     } 
  )