登录页面输入账号密码，点击登录后跳转到了一个loading的Dialog，登录成功后，关闭loading的Dialog，同时调用
Navigator.pushAndRemoveUntil(
context,
new MaterialPageRoute(builder: (context) => Home()),
(route) => route == null,
);
跳转至首页，首页有一个退出登录的地方，点出退出登录，再利用
Navigator.pushAndRemoveUntil(
context,
new MaterialPageRoute(builder: (context) => LoginPage()),
(route) => route == null,
);

此时再次登录的时候，又弹出loading的Dialog，成功后跳转首页的时候，就报了
[VERBOSE-2:ui_dart_state.cc(148)] Unhandled Exception: ‘package:flutter/src/widgets/routes.dart’: Failed assertion: line 308 pos 12: ‘!_transitionCompleter.isCompleted’: Cannot dispose a MaterialPageRoute twice.
#0 _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:40:39)
#1 _AssertionError._throwNew (dart:core-patch/errors_patch.dart:36:5)
#2 TransitionRoute.dispose (package:flutter/src/widgets/routes.dart:308:12)
#3 NavigatorState.pushAndRemoveUntil. (package:flutter/src/widgets/navigator.dart:1900:17)
#4 TickerFuture.whenCompleteOrCancel.thunk (package:flutter/src/scheduler/ticker.dart:389:15)
#5 _rootRunUnary (dart:async/zone.dart:1132:38)
#6 _CustomZone.runUnary (dart:async/zone.dart:1029:19)
#7 _FutureListener.handleValue (dart:async/future_impl.dart:126:18)
#8 Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:639:45)
#9 Future._propagateToListeners (dart:async/future_impl.dart:<…>
的异常。

我观察了一下，去掉loading的dialog，是可以正常跳转的，请问下老师这是什么原因，应该怎么解决？谢谢老师

下面是loading_dialog的代码
import ‘package:flutter/material.dart’;

// ignore: must_be_immutable
class LoadingDialog extends Dialog {
String text;

LoadingDialog({Key key, @required this.text}) : super(key: key);

@override
Widget build(BuildContext context) {
return new Material( //创建透明层
type: MaterialType.transparency, //透明类型
child: new Center( //保证控件居中效果
child: new SizedBox(
width: 120.0,
height: 120.0,
child: new Container(
decoration: ShapeDecoration(
color: Color(0xffffffff),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.all(
Radius.circular(8.0),
),
),
),
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
new CircularProgressIndicator(),
new Padding(
padding: const EdgeInsets.only(
top: 20.0,
),
child: new Text(
text,
style: new TextStyle(fontSize: 12.0),
),
),
],
),
),
),
),
);
}
}