Switch constructor Null safety

const Switch(
  1. {Key? key,
  2. required bool value,
  3. required ValueChanged<bool>? onChanged,
  4. Color? activeColor,
  5. Color? activeTrackColor,
  6. Color? inactiveThumbColor,
  7. Color? inactiveTrackColor,
  8. ImageProvider<Object>? activeThumbImage,
  9. ImageErrorListener? onActiveThumbImageError,
  10. ImageProvider<Object>? inactiveThumbImage,
  11. ImageErrorListener? onInactiveThumbImageError,
  12. MaterialStateProperty<Color?>? thumbColor,
  13. MaterialStateProperty<Color?>? trackColor,
  14. MaterialTapTargetSize? materialTapTargetSize,
  15. DragStartBehavior dragStartBehavior,
  16. MouseCursor? mouseCursor,
  17. Color? focusColor,
  18. Color? hoverColor,
  19. MaterialStateProperty<Color?>? overlayColor,
  20. double? splashRadius,
  21. FocusNode? focusNode,
  22. bool autofocus}
)

Creates a material design switch.

The switch itself does not maintain any state. Instead, when the state of the switch changes, the widget calls the onChanged callback. Most widgets that use a switch will listen for the onChanged callback and rebuild the switch with a new value to update the visual appearance of the switch.

The following arguments are required:

  • value determines whether this switch is on or off.
  • onChanged is called when the user toggles the switch on or off.

Implementation

const Switch({
  Key? key,
  required this.value,
  required this.onChanged,
  this.activeColor,
  this.activeTrackColor,
  this.inactiveThumbColor,
  this.inactiveTrackColor,
  this.activeThumbImage,
  this.onActiveThumbImageError,
  this.inactiveThumbImage,
  this.onInactiveThumbImageError,
  this.thumbColor,
  this.trackColor,
  this.materialTapTargetSize,
  this.dragStartBehavior = DragStartBehavior.start,
  this.mouseCursor,
  this.focusColor,
  this.hoverColor,
  this.overlayColor,
  this.splashRadius,
  this.focusNode,
  this.autofocus = false,
})  : _switchType = _SwitchType.material,
      assert(dragStartBehavior != null),
      assert(activeThumbImage != null || onActiveThumbImageError == null),
      assert(inactiveThumbImage != null || onInactiveThumbImageError == null),
      super(key: key);