在颤动中将double转换为Animation<double>

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: Duration(seconds: 1),
      vsync: this,
    );
    _animation = Tween<double>(begin: 0, end: 1).animate(_controller);
    _controller.forward();
  }

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Double to Animation<double>'),
        ),
        body: Center(
          child: AnimatedBuilder(
            animation: _animation,
            builder: (context, child) {
              return Opacity(
                opacity: _animation.value,
                child: Text(
                  'Hello, Flutter!',
                  style: TextStyle(fontSize: 24),
                ),
              );
            },
          ),
        ),
      ),
    );
  }
}