[BUG] Preview screen is black

[sc00n]

Sometimes (more often than not), the preview screen is fully black (as if camera is off). It is still able to scan a code though.

I tried it on moto g 5G plus (mobile) • ZY227M48LP • android-arm64 • Android 11 (API 30)

I just copied the example code from https://pub.dev/packages/qr_code_scanner
I use qr_code_scanner 0.5.2.

edit: When I close my screen for some seconds and open it up again, it starts working again.

flutter doctor -v

[√] Flutter (Channel stable, 2.2.0, on Microsoft Windows [Version 10.0.19043.1165], locale nl-BE)
    • Flutter version 2.2.0 at C:\src\flutter\flutter
    • Framework revision b22742018b (4 months ago), 2021-05-14 19:12:57 -0700
    • Engine revision a9d88a4d18
    • Dart version 2.13.0

[!] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at C:\Users\u0084978\AppData\Local\Android\sdk
    • Platform android-30, build-tools 30.0.2
    • Java binary at: C:\Program Files\Android\Android Studio2\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.

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

[√] Android Studio (version 4.1.0)
    • Android Studio at C:\Program Files\Android\Android Studio2
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)

[√] Connected device (3 available)
    • moto g 5G plus (mobile) • ZY227M48LP • android-arm64  • Android 11 (API 30)
    • Chrome (web)            • chrome     • web-javascript • Google Chrome 93.0.4577.63
    • Edge (web)              • edge       • web-javascript • Microsoft Edge 92.0.902.78

[sc00n]

The problem is when I come from a screen where the keyboard is open. In that case I get the black screen (no preview). When I first close the keyboard (and wait a second so that it is closed), I don't get the black screen and the example always works.

[radha1990kumari]

Same issue , @sc00n I believe the issue occurs when the _buildQrView in example or the QRView widget needs to resize itself . As a work around try setting resizeToAvoidBottomInset to false

[basnetjiten]

I have similar issue. When the keyboards appears and i try yo open the qrview. It shows black screen. But on closing the Keyboard and try qr it works fine

[LosDanieloss]

I'm not sure if it's connected but sounds like it could so...
Experienced issue that from end user looked similar. Black preview screen as the camera was obscured or off when device is locked and then unlocked. Simply switching front to back camera or vice-versa put things back to normal.
Hot reload also resolved for me with black screen. So my current guess it has something to do with missing controller.pause() call in some cases.

Interesting part it that this only happens on few phones running Android 11. On other devices running Android 9 or 10 we haven't seen such problems.

[RLZW]

Same is happening to me, I have a TextFormField with an Icon button which triggers the QR Scanner, one workaround that I found is to manually hide the keyboard and unfocus the scope and only then open the scanner.

FocusScope.of(context).unfocus();
SystemChannels.textInput.invokeMethod('TextInput.hide');

[allanctan]

Same issue , @sc00n I believe the issue occurs when the _buildQrView in example or the QRView widget needs to resize itself . As a work around try setting resizeToAvoidBottomInset to false

Thank you. This solves my problem.

[Joshfindit]

I currently have this issue with the example app and a Pixel 3 with the latest OS.

How I reproduce:

1. Open qrView
2. Turn the phone to landscape
3. Turn the phone back to portrait (sometimes the preview is black only after step 2, sometimes step 3 is required)

Possibly relevant debug logs:

Setup

...
I/CenterCropStrategy(24527): Preview: 1200x1600; Scaled: 1216x1622; Want: 1080x1622
I/CameraPreview(24527): Starting preview
D/CameraInstance(24527): Starting preview
I/AutoFocusManager(24527): Current focus mode 'auto'; use auto focus? true
W/System  (24527): A resource failed to call release.

Rotating to landscape:

D/CameraPreview(24527): resume()
W/CameraPreview(24527): initCamera called twice
D/CameraPreview(24527): resume()
W/CameraPreview(24527): initCamera called twice
D/CameraPreview(24527): resume()
W/CameraPreview(24527): initCamera called twice

This is with a single turn to 90 degrees, and preview is black

Turning it back to portrait:

D/CameraPreview(24527): resume()
W/CameraPreview(24527): initCamera called twice
D/CameraPreview(24527): resume()
W/CameraPreview(24527): initCamera called twice
D/CameraPreview(24527): resume()
W/CameraPreview(24527): initCamera called twice

Preview is still black. Pressing pause and resume does bring it back.

Note: I also tried resizeToAvoidBottomInset: false, but that made no difference.

[hm122]

Can confirm the problem. A quick (dirty) fix is:

  @override
  Widget build(BuildContext context) {
    if(controller != null && mounted) {
      controller!.pauseCamera();
      controller!.resumeCamera();
    }
    ...

Has anybody a more elegant solution?

[xiongcaichang]

mark

[moradiyajay]

Any solutions ?

[RAJANIBHOOMI]

any solution

[fzyzcjy]

hi, is there any updates?

[AndresTapiero]

HI, is there any updates?

[nicks258]

Any updates. This is causing serious issues now.