Flutter apply method to static variable-CodePudding

How do you apply a method to a static variable from a class. There are certain built in classes in flutter that appear to do something like this.

class UITextStyle {
  static const TextStyle body = TextStyle(fontSize: 17);

   addColor(Color color) {
    TextStyle style = this as TextStyle;
    style.merge(TextStyle(color: color));
  }
}

Which can then be called like this:

UITextStyle.body.addColor(Color.fromRGBA(0,0,0,1));

However I cannot call that method like that as firstly it is not static, and secondly if it were I would not be able to call it after declaring .body first and would only be able to call it at UITextStyle.addColor(...).

How is this achieved?

CodePudding user response：

you can try this solution , the point is that addColor function is not defined to the TextStyle Type , so to achieve that you need to add this function to the TextStyle class by this extension :

extension TextStyleEx on TextStyle{

  TextStyle addColor(Color color) {
    return merge(TextStyle(color: color,fontWeight: FontWeight.w600));
  }

}

and make this method return TextStyle so you can get instance from the merged ones , cause your static object is final so you can not receive new value on it.

and leave your class like this

  class UITextStyle {
    static const TextStyle body = TextStyle(fontSize: 17);
  }

use this class and the saved static object to get new TextStyle with the old and the new TextStyles.

for test run this in main , will clear the previous example :

TextStyle mergedStyles = UITextStyl.body.addColor(Colors.black);
print(mergedStyles);

CodePudding user response：

Thanks to the comments from @pskink I was eventually able to get this functioning.

class UITextStyle {
  const UITextStyle(this.style);
  final TextStyle style;
  static const body = UITextStyle(TextStyle(fontSize: 17));

  addColor(Color color) {
    TextStyle textStyle = style;
    return textStyle.merge(TextStyle(color: color));
  }
}

CodePudding user response：

In Dart extensions can have static members.

extension UITextStyle on TextStyle {
  static const body = TextStyle(fontSize: 17);
  
  TextStyle addColor(Color color) {
    return this.merge(TextStyle(color: color));
  }
}

You can then do:

UITextStyle.body.addColor(Color.fromRGBO(0, 0, 0, 1));