如何在Dart中向现有类添加构造函数？

Question

I'd like to make some convenience/factory constructors for a few common UI classes. For example, TextStyle:

enum Font {
  AvenirNext,
  AvenirNextCondensed
}

enum Weight {
  Regular,
  Medium,
  DemiBold,
  Bold
}

// Use:
// TextStyle(Fonts.AvenirNext, Weight.Medium, 20, Colors.white)

// Maybe it can be even shorter?
// TextStyle(AvenirNext, Medium, 20, Colors.black)

How to go about this in Dart?

Answer 1

How about extending TextStyle like below

class Font {
  static const AvenirNext = 'AvenirNext';
  static const AvenirNextCondensed = 'AvenirNextCondensed';
}

class Weight{
  static const Regular = FontWeight.w400;
  static const Medium = FontWeight.w500;
  static const DemiBold = FontWeight.w700;
  static const Bold = FontWeight.w900;
}

class CTextStyle extends TextStyle {
  CTextStyle(String f, FontWeight w, num s, Color c)
      : super(
          fontFamily: f,
          fontWeight: w,
          fontSize: s.toDouble(),
          color: c);
  }
}

usage:

TextStyle myCustom = CTextStyle(Font.AvenirNext, Weight.Medium, 20, Colors.black);