updateMaterialState method Null safety

  1. @protected
ValueChanged<bool> updateMaterialState(
  1. MaterialState key,
  2. {ValueChanged<bool>? onChanged}
)
protected">@protected

Callback factory which accepts a MaterialState value and returns a closure to mutate materialStates and call setState.

Accepts an optional second named parameter, onChanged, which allows arbitrary functionality to be wired through the MaterialStateMixin. If supplied, the onChanged function is only called when child widgets report events that make changes to the current set of MaterialStates.

link
This example shows how to use the updateMaterialState callback factory in other widgets, including the optional onChanged callback. 
class MyWidget extends StatefulWidget {
  const MyWidget({super.key, this.onPressed});

  /// Something important this widget must do when pressed.
  final VoidCallback? onPressed;

  @override
  State<MyWidget> createState() => MyWidgetState();
}

class MyWidgetState extends State<MyWidget> with MaterialStateMixin<MyWidget> {
  @override
  Widget build(BuildContext context) {
    return Container(
      color: isPressed ? Colors.black : Colors.white,
      child: InkWell(
        onHighlightChanged: updateMaterialState(
          MaterialState.pressed,
          onChanged: (bool val) {
            if (val) {
              widget.onPressed?.call();
            }
          },
        ),
      ),
    );
  }
}

Implementation

@protected
ValueChanged<bool> updateMaterialState(MaterialState key, {ValueChanged<bool>? onChanged}) {
  return (bool value) {
    if (materialStates.contains(key) == value) {
      return;
    }
    setMaterialState(key, value);
    onChanged?.call(value);
  };
}