进度条LinearProgressIndicator

LinearProgressIndicator

进度条有两类，一个是有具体值，另一个没有

 late AnimationController controller;

 @override
 void initState() {
   controller = AnimationController(
     vsync: this,
     duration: const Duration(seconds: 5),
   )..addListener(() {
       setState(() {});
     });
   controller.repeat(reverse: true);
   super.initState();
 }

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

Widget build(BuildContext context) {
  return Scaffold(
    body: Padding(
      padding: const EdgeInsets.all(20.0),
      child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: [
          Text(
            'Linear progress indicator with a fixed color',
            style: const TextStyle(fontSize: 20),
          ),
          LinearProgressIndicator(
            value: controller.value,
            semanticsLabel: 'Linear progress indicator',
          ),
        ],
      ),
    ),
  );
}