Step({@required Widget title, Widget subtitle, @required Widget content, StepState state: StepState.indexed, bool isActive: false })

Creates a step for a Stepper.

The title, content, and state arguments must not be null.

Source 

Step({
  @required this.title,
  this.subtitle,
  @required this.content,
  this.state: StepState.indexed,
  this.isActive: false
}) {
  assert(this.title != null);
  assert(this.content != null);
  assert(this.state != null);
}