MaterialStateUnderlineInputBorder class abstract

Defines a UnderlineInputBorder that is also a MaterialStateProperty.

This class exists to enable widgets with UnderlineInputBorder valued properties to also accept MaterialStateProperty<UnderlineInputBorder> values. A material state input border property represents an input border which depends on a widget's "interactive state". This state is represented as a Set of MaterialStates, like MaterialState.pressed, MaterialState.focused and MaterialState.hovered.

MaterialStateUnderlineInputBorder should only be used with widgets that document their support, like InputDecoration.border.

To use a MaterialStateUnderlineInputBorder, you can either:

1. Create a subclass of MaterialStateUnderlineInputBorder and implement the abstract resolve method.
2. Use MaterialStateUnderlineInputBorder.resolveWith and pass in a callback that will be used to resolve the color in the given states.

If a MaterialStateUnderlineInputBorder is used for a property or a parameter that doesn't support resolving MaterialStateProperty<UnderlineInputBorder>s, then its default color value will be used for all states.

To define a const MaterialStateUnderlineInputBorder, you'll need to extend MaterialStateUnderlineInputBorder and override its resolve method. You'll also need to provide a defaultValue to the super constructor, so that we can know at compile-time what its default color is.