Flutter，如何在没有按钮触发器的情况下自动设置动画

dependencies:
  flutter_animation_progressions: ^版本号

AnimationController controller = AnimationController(
  duration: Duration(seconds: 2),
  vsync: this,
);

Animation<double> animation = CurvedAnimation(
  parent: controller,
  curve: Curves.easeInOut,
);

Animation<double> animation = Tween<double>(
  begin: 0.0,
  end: 1.0,
).animate(controller);

animation.addStatusListener((status) {
  if (status == AnimationStatus.completed) {
    // 动画完成后的操作
  }
});

controller.forward();

import 'package:flutter/material.dart';
import 'package:flutter_animation_progressions/flutter_animation_progressions.dart';

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> with SingleTickerProviderStateMixin {
  AnimationController controller;
  Animation<double> animation;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      duration: Duration(seconds: 2),
      vsync: this,
    );
    animation = CurvedAnimation(
      parent: controller,
      curve: Curves.easeInOut,
    );
    animation = Tween<double>(
      begin: 0.0,
      end: 1.0,
    ).animate(controller);
    animation.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        // 动画完成后的操作
      }
    });
    controller.forward();
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: AnimatedBuilder(
          animation: animation,
          builder: (BuildContext context, Widget child) {
            return Opacity(
              opacity: animation.value,
              child: child,
            );
          },
          child: Container(
            width: 200,
            height: 200,
            color: Colors.blue,
          ),
        ),
      ),
    );
  }
}