default values in dart constructor

Question

I have the following class which has required unpressedImage field. I need to set unpressedImage value to pressedImage field if pressedImage is not specified. How can I achieve this the best way?

class ImageButton extends StatefulWidget {
  final Image unpressedImage;
  final Image pressedImage;
  final onTap;

  const ImageButton({
    Key key,
    @required this.unpressedImage,
    this.pressedImage,
    this.onTap,
  }) : super(key: key);

  @override
  _ImageButtonState createState() => _ImageButtonState();
}

Stephen · Accepted Answer · 2020-07-21 18:45:45Z

5

Set it in the initialization list, and use a conditional to pick which value you want to use:

class ImageButton extends StatefulWidget {
  final Image unpressedImage;
  final Image pressedImage;
  final onTap;

  const ImageButton({
    Key key,
    @required this.unpressedImage,
    Image pressedImage,
    this.onTap,
  })  : this.pressedImage =
            pressedImage == null ? unpressedImage : pressedImage,
        super(key: key);

  @override
  _ImageButtonState createState() => _ImageButtonState();
}

edited Jul 21, 2020 at 18:45

answered Jul 21, 2020 at 18:38

Stephen

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2 Comments

julemand101 Over a year ago

Just want to add that you can simplify it with this.pressedImage = pressedImage ?? unpressedImage : dart.dev/guides/language/language-tour#conditional-expressions

Stephen Over a year ago

@julemand101 Ah yes. That's cleaner isn't it. Thanks for the improvement.

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