NavigationItem constructor
      const
      NavigationItem({ 
    
    
- Key? key,
- AbstractButtonStyle? selectedStyle,
- bool? selected,
- ValueChanged<bool> ? onChanged,
- Widget? label,
- double? spacing,
- AbstractButtonStyle? style,
- AlignmentGeometry? alignment,
- int? index,
- bool? enabled,
- NavigationOverflow overflow = NavigationOverflow.marquee,
- AlignmentGeometry? marginAlignment,
- required Widget child,
Implementation
const NavigationItem({
  super.key,
  this.selectedStyle,
  this.selected,
  this.onChanged,
  super.label,
  super.spacing,
  super.style,
  super.alignment,
  this.index,
  super.enabled,
  super.overflow,
  super.marginAlignment,
  required super.child,
});