Camera Preview Freezes upon Reopening MobileScanner Widget

[jeremyLACLICK]

Hi there,

Thank you for the great package! Recently, the camera preview freezes whenever I open the widget containing it for the second time. I have the same issue when running my web app in the debugger and after deploying it. I also have this issue when running the project provided in the 'example' folder of this repository.

It is possible that the problem is due to an incompatibility with the most recent Dart update?

I noticed that when I pass the controller as a parameter of the Widget that contains the MobileScanner, the camera preview no longer freezes when it is opened for the second time. Does the issue then relate to the way I am using the MobileScannerController?

Test.txt

Best, Jeremy

[navaronbracke]

I noticed that when I pass the controller as a parameter of the Widget that contains the MobileScanner, the camera >preview no longer freezes when it is opened for the second time.

That sounds like the bug with the lifecycle management. Are you using version 4.0.x ? You could try validating with the new beta, 5.0.0-beta.1, which removes internal lifecycle management of the controller from the MobileScanner widget.

That bug caused issues with widget tree reparenting, so we removed the lifecycle management from the plugin.

You can use the updated example app from this beta version to validate. It also includes updates to the web support, using the new JS interop that was introduced with Dart 3.3

[jeremyLACLICK]

Hi there,

I am indeed using version 4.0.1. I will give the beta version a try, although I can see it is incompatible with another one of my project's dependencies.

Thank you in any case for the help!

[lavinov-mercury]

Seems like it's related not to lib changes, but to the Flutter upgrade. It started reproducing with 3.19.0 stable version, no matter which version of the lib is used (tried 5.0.0 as well). With 3.16.9 the issue is not reproducible for me. (all tested with the example app)

[navaronbracke]

Strange, that could be an issue with Platform Views then. I will investigate further.

[jeremyLACLICK]

Thanks!

[romawizard]

Any updates?

[navaronbracke]

I noticed that when I pass the controller as a parameter of the Widget that contains the MobileScanner, the camera preview no longer freezes when it is opened for the second time.

For anyone asking for updates: You should provide a MobileScannerController to the MobileScanner widget. This is the recommended way to do things and will be the only way to use the widget starting from version 5.0.0

[wkok]

I noticed that when I pass the controller as a parameter of the Widget that contains the MobileScanner, the camera preview no longer freezes when it is opened for the second time.

For anyone asking for updates: You should provide a MobileScannerController to the MobileScanner widget. This is the recommended way to do things and will be the only way to use the widget starting from version 5.0.0

Hello,

Providing a MobileScannerController to the MobileScanner widget works to not have the camera preview freeze when it's opened the second time, however, the actual scanning of a barcode only works on the first attempt of the preview being opened, not the second etc.. until I refresh the browser, the barcode scans the first time but then not again on subsequent attempts.

[fg0611]

Hi I have a similar issue in Flutter Web. The camera stops/freezes after mounting the same widget that uses MobileScanner widget. I'm using the controller just like in the example for package version 5.0.0-beta.2 with everything else using WidgetsBindingObserver, StreamSubscription and the function called didChangeAppLifecycleState as is.

With package version 5.0.0-beta.2 I'm using flutter 3.19.5, dart 3.3.3.

Adding to that, I'm getting this browser message library@0.19.1:15 Trying to play video that is already playing. could it be related to the freezing?

I had the same problem using package version 4.0.1 and 3.5.7 with flutter older version and dart older version too.

[joymyr]

Im having the same issue as @fg0611, and it seems like web support was broken in 5.0.0-beta.1

[navaronbracke]

I did fix an issue with an unsupported MediaTrackSettings field earlier this morning. Did you get an Null is not a subtype of String error on the web?

I also need to look into an issue on Android, relating to the new lifecycle handling. On Android, the permission popup triggers a lifecycle change. Which, when combined with the recommendation on "restarting" the scanner when the app is resumed, results in a bug with the permission popup being requested again when tapping "Deny".

[joymyr]

No, I'm getting Trying to play video that is already playing even the first time calling start

[navaronbracke]

No, I'm getting Trying to play video that is already playing even the first time calling start

Then what did you mean by it seems like web support was broken in 5.0.0-beta.1 ? The message above seems harmless (although I still need to figure out what is causing it)

[fg0611]

I'm using the example with controller. To reproduce:

• Home() with a Nav.push(cxt, scannerWidget)
• go back with a button Nav.pop()
• then click again to see scanner (it appears freezed).

[joymyr]

Sorry, I just assumed the message was related to why it isn't working The issue is that the MobileScanner widget is just displaying a black screen, with an exclamation mark inside. I'm not seeing any other error messages.

[fg0611]

Sorry, I just assumed the message was related to why it isn't working The issue is that the MobileScanner widget is just displaying a black screen, with an exclamation mark inside. I'm not seeing any other error messages.

may I ask if you inserted ` <script src="https://unpkg.com/@zxing/library@0.19.1" type="application/javascript"

` inside index.html file?

[navaronbracke]

Sorry, I just assumed the message was related to why it isn't working The issue is that the MobileScanner widget is just displaying a black screen, with an exclamation mark inside. I'm not seeing any other error messages.

Do you have errors in the browser console?

The white exclamation mark on the black background is the default error builder for the MobileScanner() widget. Can you pass a custom widget, and then get the stack trace from the error details of the MobileScannerException, or Exception if for some reason we didn't catch it properly.

[joymyr]

I tried to deploy to a server now, and it works, so the issue seems to be only when running on localhost/debug mode. Still having the freezing issue on reopening though. When debugging locally I get no errors in the console, but from the errorBuilder I get TypeError: null: type 'Null' is not a subtype of type 'String'.

[navaronbracke]

I tried to deploy to a server now, and it works, so the issue seems to be only when running on localhost/debug mode. Still having the freezing issue on reopening though. When debugging locally I get no errors in the console, but from the errorBuilder I get TypeError: null: type 'Null' is not a subtype of type 'String'.

Yeah, the TypeError: null: type 'Null' is not a subtype of type 'String' is the issue I fixed locally. I still want to prepare some other changes for beta 3 (the iOS privacy manifest being one of those)

I currently have the local fix on

  mobile_scanner:
    git:
      url: https://github.com/navaronbracke/mobile_scanner.git
      ref: 5_0_0-beta-3

if you want to tinker with it.

[navaronbracke]

I'm using the example with controller. To reproduce:

• Home() with a Nav.push(cxt, scannerWidget)
• go back with a button Nav.pop()
• then click again to see scanner (it appears freezed).

I can reproduce this bug with the example app. I don't see any errors in the console, except for a Canvas2D warning.

[navaronbracke]

Small update: I managed to fix the "frozen" camera preview locally. Still need to figure out why the ZXing barcode reader is not scanning the frames on the second attempt, but once that is done, this bug should be fixed.

[joymyr]

Great, both the freezing and the TypeError: null is fixed with beta 3

[fg0611]

Small update: I managed to fix the "frozen" camera preview locally. Still need to figure out why the ZXing barcode reader is not scanning the frames on the second attempt, but once that is done, this bug should be fixed.

Thank you in advance!. If it's not too much to ask, could you please leave a route with a working demo and access to the code?