第九章：自定义AnimatedDecoratedBox异常

[chawson]

Field '_decoration' has not been initialized

https://github.com/flutterchina/flutter_in_action_2nd/blob/main/src/chapter9/animated_widgets.md?plain=1#L162

late DecorationTween _decoration;

可修改为

DecorationTween? _decoration;

https://github.com/flutterchina/flutter_in_action_2nd/blob/main/src/chapter9/animated_widgets.md?plain=1#L167

return DecoratedBox(
   decoration: _decoration.evaluate(animation),
   child: widget.child,
);

可修改为

return DecoratedBox(
  decoration: _decoration!.evaluate(animation),
  child: widget.child,
);