Assertion failed: "onGenerateRoute" shows assertion when I try to go the same route for the 2nd time.

Condition:

using Chrome-Develop for the web
using "flutter channel master" 2019-11-5 tokyo
("flutter version" shows tons of v 1.XX.XX . so I am not sure what to write here)

Step:

With the code below, start the app by "flutter run -d chrome"
2.Click "to the Home" button.
3.Click "to the Root" button.
4.You see the Red Screen with the assertion message.

Comment:

as you can see from the code, I have tested using onGenerateRoute with the switch case. This works.
but what I want to achieve is to create routing table from setting file. which probably need Map

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  final Map rootMap;
  MyApp():
    rootMap = {
      "/": MaterialPageRoute(builder:(context) => Root()),
      '/Home': MaterialPageRoute(builder:(context) => Home()),
    };

  Route<dynamic> generateRouteByMap(RouteSettings settings) {
    if(rootMap[settings.name] != null){
      return rootMap[settings.name];
    }
    else{
      return MaterialPageRoute(builder:(context) => Root());
    }
  }

  Route<dynamic> generateRouteBySwitch(RouteSettings settings) {
    switch(settings.name){
      case "/Home":
        return MaterialPageRoute(builder:(context) => Home());
      default:
        return MaterialPageRoute(builder:(context) => Root());
    }
  }
  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Reproduce',
        // routes: {
        //   "/": (context) => Root(),
        //   "/Home": (context) => Home(),
        // },
      //  onGenerateRoute: generateRouteBySwitch,
      onGenerateRoute: generateRouteByMap,
    );
  }
}

class Root extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(
      children: <Widget>[
        Text("Root"),
        FlatButton(
          child: Text("to the Home"),
          onPressed: () {
            Navigator.popAndPushNamed(context, "/Home");
          },
        ),
      ],
    );
  }
}

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(
      children: <Widget>[
        Text("home"),
        FlatButton(
          child: Text("to The Root"),
          onPressed: () {
            Navigator.popAndPushNamed(context, "/");
          },
        ),
      ],
    );
  }
}

and the Assertion message is following
══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
The following assertion was thrown while handling a gesture:
Assertion failed: org-dartlang-app:///packages/flutter/src/widgets/navigator.dart:1788:12
route._navigator == null
is not true
package:flutter/src/gestures/binding.dart 156:7
[_handlePointerEvent]
package:flutter/src/gestures/binding.dart 102:7
[_flushPointerEventQueue]
package:flutter/src/gestures/binding.dart 86:32
[_handlePointerDataPacket]
package:build_web_compilers/src/dev_compiler/C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/pointer_binding.dart 89:15
[_onPointerData]
package:build_web_compilers/src/dev_compiler/C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/pointer_binding.dart 261:7
package:build_web_compilers/src/dev_compiler/C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/pointer_binding.dart 173:16

Handler: "onTap"
Recognizer:
TapGestureRecognizer#0a0fa
════════════════════════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: Assertion failed: org-dartlang-app:///packages/flutter/src/widgets/navigator.dart:2330:12

@ClozedJP

Hi @ClozedJP
thank you for reporting that,
I noticed that it occurs also with the demo code

doctor

[√] Flutter (Channel dev, v1.10.14, on Microsoft Windows [Version 10.0.18362.10024], locale en-US)
    • Flutter version 1.10.14 at C:\src\flutter
    • Framework revision 1946fc4da0 (4 weeks ago), 2019-10-07 15:23:31 -0700
    • Engine revision 1d62160fdb
    • Dart version 2.6.0 (build 2.6.0-dev.5.0 d6c6d12ebf)


[√] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    • Android SDK at C:\Users\iapic\AppData\Local\Android\sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-28, build-tools 28.0.3
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 3.5)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 40.0.2
    • Dart plugin version 191.8423
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)

[√] VS Code, 64-bit edition (version 1.39.2)
    • VS Code at C:\Program Files\Microsoft VS Code
    • Flutter extension version 3.6.0

[√] Connected device (2 available)
    • Chrome          • chrome          • web-javascript • Google Chrome 77.0.3865.120
    • Headless Server • headless-server • web-javascript • Flutter Tools

• No issues found!

I just came up with alternate of achieving what I want.
Just in case someone want to do the same stuff, I leave the code here.
update: somehow, sometimes work without 'routes: {"/": (context) => Loading(), }'sometimes not.

class Alternateway extends StatelessWidget {
  static final int initialVal = 0;
  static final int finalVal = 9;
  final Map widgetMap = {};
  Alternateway() {    
    for (int i = initialVal; i < finalVal + 1; i++) {
      TextWithButton twb = TextWithButton(i);
      widgetMap[i.toString()] = twb;
    }
  }

  Route<dynamic> generateRouteBySwitchTest(RouteSettings settings) {
    print("settings.name:" + settings.name);
    Widget target = widgetMap[settings.name];
    if(target == null){
      target = widgetMap["0"];
    }    
    return MaterialPageRoute(builder: (context) => target);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Reproduce',
      routes: {"/": (context) => widgetMap["0"], },
      onGenerateRoute: generateRouteBySwitchTest,
    );
  }
}

class TextWithButton extends StatelessWidget {
  final int current;

  TextWithButton(int current)
      : this.current = current;
  @override
  Widget build(BuildContext context) {
    List<Widget> lw = [];
    int pre = current - 1;
    int next = current + 1;
    lw.add(Text("Current:" + current.toString()));
    if (current > Alternateway.initialVal)
      lw.add(FlatButton(
        child: Text("go to:" + pre.toString()),
        onPressed: () {
          Navigator.popAndPushNamed(context, pre.toString());
        },
      ));
    if (current < Alternateway.finalVal)
      lw.add(FlatButton(
        child: Text("go to:" + next.toString()),
        onPressed: () {
          Navigator.popAndPushNamed(context, next.toString());
        },
      ));
    return Row(
      children: lw,
    );
  }
}

@goderbauer

/cc @goderbauer this is an example of a confusing behavior in the navigator when the route is push again after being popped out of and disposed. This is not a web-only issue, so removing the web label.

It would be nice if I am able to chose "Always dispose" vs "Always Keep."
just like "maintainState" property in "MaterialPageRoute" class.

More Info:
I meet the error while I was looking for the alternate to this case. I am not able to make it simple.
This error must be related or similar to this case. I hope this will help.
Error massage is below.

══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
The following assertion was thrown while handling a gesture:
Assertion failed: org-dartlang-app:///packages/flutter/src/widgets/navigator.dart:2113:12
!_debugLocked
is not true

Either the assertion indicates an error in the framework itself, or we should provide substantially
more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new?template=BUG.md

When the exception was thrown, this was package:build_web_compilers/src/dev_compiler/C:/b package:build_web_compilers/src/dev_compiler/C:/b package:flutter/src/widgets/navigator.dart 2113:13 package:flutter/src/widgets/navigator.dart 1736:5 package:flutter/src/material/ink_well.dart 706:14 package:flutter/src/material/ink_well.dart 789:36 package:flutter/src/gestures/recognizer.dart 182:24 package:flutter/src/gestures/tap.dart 486:47 package:flutter/src/gestures/tap.dart 264:5 package:flutter/src/gestures/tap.dart 236:7 package:flutter/src/gestures/arena.dart 156:12 package:flutter/src/gestures/binding.dart 222:20 package:flutter/src/gestures/binding.dart 198:14 package:flutter/src/gestures/binding.dart [_handlePointerEvent]
package:flutter/src/gestures/binding.dart [_flushPointerEventQueue]
package:flutter/src/gestures/binding.dart [_handlePointerDataPacket]
package:build_web_compilers/src/dev_compiler/C:/b [_onPointerData]
package:build_web_compilers/src/dev_compiler/C:/b package:build_web_compilers/src/dev_compiler/C:/b the stack:
/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/internal/js_dev_runtime/private/ddc_runtime/errors.dart 194:49 throw
/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 24:3 assertFailed
pop
popAndPushNamedpackage:flutter/src/widgets/navigator.dart 1027:32 popAndPushNamedpackage:adventure/adventure/visual/ActionBars.dart 56:33
[_handleTap]

invokeCallback
handleTapUp
[_checkUp]
acceptGesture
sweep
handleEvent
dispatchEvent
156:7
102:7
86:32
/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/pointer_binding.dart 89:15
/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/pointer_binding.dart 261:7
/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/pointer_binding.dart 173:16

Handler: "onTap"
Recognizer:
TapGestureRecognizer#ac7dd

@iapicca

@iapicca The example you link to works as expected for me.

In general, it is not a good idea to re-use route objects (they have a lifecycle of their own and if you re-push the same Route object you will run into problems). Whenever you push a route you want to provide a new Route object. So, in your generateRouteByMap you probably always want to create a new MaterialPageRoute and populate it with a builder from a Map or something like that.

In this particular case the problem is that you currently cannot pop the first route off the history stack. So, your first call to Navigator.popAndPushNamed(context, "/Home"); will not remove the route / from the history because it is the first route. When you then call Navigator.popAndPushNamed(context, "/"); you are essentially pushing a Route object that's already on the history stack and that's when the exception throws because one-and-the-same Route object cannot be on the stack twice.

@goderbauer

thx for reply @goderbauer I understand the 1st paragraph.

Re-use of route objects is prohibited.
Even if I want to use the route with same name, I should make the new route object
My alternate is the way to go since it ”new MaterialPageRoute and populate it with a builder from a Map”

But, I am not sure about 2nd paragraph.
You say “...So, your first call to Navigator.popAndPushNamed(context, "/Home"); will not remove the route...”
yet, if i pop the “/Home” then the “/” is not exist, there was white screen. I think the "/" is poped.
However, I think this is not the focus of the topic here.

Anyway, I understand this is not a bug, but The error message is not user friendly.
I think, this is very common mistake we would make for 1st time.
It would be nice if the error message was saying about “not a good idea to re-use route objects (they ... problems)”

If you want me to close this case let me know.

Yes, the assert on this line [1] should have an error message telling you that the pushed route has already been used.

[1]

flutter/packages/flutter/lib/src/widgets/navigator.dart

Line 1788 in 99055c7

assert(route._navigator == null);

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

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Assertion failed: "onGenerateRoute" shows assertion when I try to go the same route for the 2nd time. #44128

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Assertion failed: "onGenerateRoute" shows assertion when I try to go the same route for the 2nd time. #44128

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iapicca commented on Nov 5, 2019

ClozedJP commented on Nov 7, 2019

yjbanov commented on Nov 7, 2019

ClozedJP commented on Nov 8, 2019

ClozedJP commented on Nov 8, 2019

goderbauer commented on Nov 11, 2019

ClozedJP commented on Nov 12, 2019

goderbauer commented on Nov 12, 2019

github-actions commented on Aug 19, 2021

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