key method
Assigns a Key to this widget.
Keys are used to preserve state when widgets move around in the tree. This method provides a fluent way to assign a key to a widget.
Example:
Container().key(GlobalKey()),
Text('Hello').key(UniqueKey()),
Implementation
Widget key(Key key) {
return _WidgetWrapper._wrapOrCopyWith(
child: this,
key: () => key,
);
}