appbar中的标题字体在颤动中不变

import 'package:flutter/material.dart';

class ShakingAppBar extends StatefulWidget implements PreferredSizeWidget {
  final String title;

  ShakingAppBar({Key key, this.title}) : super(key: key);

  @override
  _ShakingAppBarState createState() => _ShakingAppBarState();

  @override
  Size get preferredSize => Size.fromHeight(kToolbarHeight);
}

class _ShakingAppBarState extends State<ShakingAppBar>
    with SingleTickerProviderStateMixin {
  AnimationController _animationController;
  Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _animationController = AnimationController(
      vsync: this,
      duration: Duration(milliseconds: 500),
    )..repeat(reverse: true);
    _animation = Tween<double>(begin: -2.0, end: 2.0).animate(
      CurvedAnimation(
        parent: _animationController,
        curve: Curves.easeInOut,
      ),
    );
  }

  @override
  void dispose() {
    _animationController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _animationController,
      builder: (BuildContext context, Widget child) {
        return AppBar(
          title: Transform.translate(
            offset: Offset(_animation.value, 0),
            child: Text(widget.title),
          ),
          actions: [
            IconButton(
              icon: Icon(Icons.search),
              onPressed: () {},
            ),
          ],
        );
      },
    );
  }
}