Flutter 实现进度条效果

LinearProgressIndicator(
 value: 0.3,
 valueColor: AlwaysStoppedAnimation<Color>(Colors.red),
 backgroundColor: Colors.blue,
),

import 'package:flutter/material.dart';

class ProgressDemo extends StatefulWidget {
 ProgressDemo({Key key}) : super(key: key);

 @override
 _ProgressDemoState createState() => _ProgressDemoState();
}

class _ProgressDemoState extends State<ProgressDemo> {
 @override
 Widget build(BuildContext context) {
 return Scaffold(
  appBar: AppBar(
  title: Text('flutter progress demo'),
  ),
  body: Container(
  margin: EdgeInsets.only(top: 20),
  alignment: Alignment.topCenter,
  child: FlatButton(
   child: Text('进度'),
   color: Colors.blue,
   onPressed: () {
   return showDialog(context: context, builder: (context) {
    return AlertDialog(
    backgroundColor: Colors.transparent,
    title: Text('上传中...'),
    content: LinearProgressIndicator(
     value: 0.3,
     valueColor: AlwaysStoppedAnimation<Color>(Colors.red),
     backgroundColor: Colors.blue,
    ),
    shape: RoundedRectangleBorder(
     borderRadius: BorderRadius.all(Radius.circular(10))
    ),
    );
   },);
   },
  ),
  ),
 );
 }
}