dart - getter 'value' 在 null 上被调用

Question

我正在尝试在 flutter 中创建此字体大小动画，但我收到以下错误:getter 'value' was called on null。

这看起来很奇怪，因为我有另一个包含类似代码的 dart 文件并且它运行良好。

如有任何帮助，我们将不胜感激。

Animation<double> _fontSizeAnimation;
AnimationController _fontSizeAnimationController;

初始化状态函数():

super.initState();
_fontSizeAnimationController = new AnimationController(
    duration: new Duration(milliseconds: 500), vsync: this);
_fontSizeAnimation = new CurvedAnimation(
    parent: _fontSizeAnimationController, curve: Curves.bounceOut);
_fontSizeAnimation.addListener(() => this.setState(() {}));
_fontSizeAnimationController.forward();

Material 小部件

  return new Material(
  color: Colors.blueAccent,
  child: new InkWell(
    onTap: () => print("We tapped the page!"),
    child: new Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        new Text("Let's Quizzz",
            style: new TextStyle(
                color: Colors.white,
                fontSize: _fontSizeAnimation.value * 15,
                fontWeight: FontWeight.bold)),
        new Text("Tap to start!",
            style: new TextStyle(
                color: Colors.white,
                fontSize: 20.0,
                fontWeight: FontWeight.bold))
      ],
    ),
  ),
);

Answer 1

我遇到了同样的空警告。更改 _fontSizeAnimation.value 没有 null 错误 ...

  children: <Widget>[
    new Text("Let's Quizzz",
        style: new TextStyle(
            color: Colors.white,
            fontSize: (_fontSizeAnimation.value + 1) * 15,
            fontWeight: FontWeight.bold)),
    new Text("Tap to start!",
        style: new TextStyle(
            color: Colors.white,
            fontSize: 20.0,
            fontWeight: FontWeight.bold))
  ],