mobile_scanner

To prevent the scanner from running while the app is inactive, manually manage the lifecycle using WidgetsBindingObserver.

Steps:

1. Initialize MobileScannerController with autoStart: false.
2. Mix in WidgetsBindingObserver to your State class.
3. In didChangeAppLifecycleState:
   • When resumed: Listen to controller.barcodes and call controller.start().
   • When inactive: Cancel the subscription and call controller.stop().
4. In initState: Add the observer and start the scanner.
5. In dispose: Remove the observer, cancel subscriptions, and call controller.dispose().

class MyState extends State<MyStatefulWidget> with WidgetsBindingObserver {
  final MobileScannerController controller = MobileScannerController(autoStart: false);
  StreamSubscription<Object?>? _subscription;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    _subscription = controller.barcodes.listen(_handleBarcode);
    unawaited(controller.start());
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (!controller.value.hasCameraPermission) return;

    switch (state) {
      case AppLifecycleState.detached:
      case AppLifecycleState.hidden:
      case AppLifecycleState.paused:
        return;
      case AppLifecycleState.resumed:
        _subscription = controller.barcodes.listen(_handleBarcode);
        unawaited(controller.start());
        break;
      case AppLifecycleState.inactive:
        unawaited(_subscription?.cancel());
        _subscription = null;
        unawaited(controller.stop());
        break;
    }
  }

  @override
  Future<void> dispose() async {
    WidgetsBinding.instance.removeObserver(this);
    unawaited(_subscription?.cancel());
    _subscription = null;
    super.dispose();
    await controller.dispose();
  }
}

The scanWindow property allows you to define a specific Rect area within the MobileScanner widget's layout. The scanner will only detect barcodes that intersect this rectangle.

Important Notes:

• Web Support: scanWindow is not supported on the web because the scanner does not expose barcode size information there.
• Coordinate System: The rectangle is relative to the layout size of the MobileScanner widget in the widget tree, not the raw camera output size. The fit property (e.g., BoxFit.cover) affects how this window is mapped to the camera texture.
• Performance: If updating the scan window causes performance issues, use scanWindowUpdateThreshold to prevent frequent updates when layout constraints change slightly.

Example: Centered Scan Window

To create a scan window that is centered and occupies a specific portion of the widget's size:

LayoutBuilder(
  builder: (BuildContext context, BoxConstraints constraints) {
    final Size layoutSize = constraints.biggest;

    final double scanWindowWidth = layoutSize.width / 3;
    final double scanWindowHeight = layoutSize.height / 2;

    final Rect scanWindow = Rect.fromCenter(
      center: layoutSize.center(Offset.zero),
      width: scanWindowWidth,
      height: scanWindowHeight,
    );

    return MobileScanner(
      scanWindow: scanWindow,
      // ... other properties
    );
  },
);

The MobileScannerState class represents the current status of a MobileScannerController. It provides real-time information about the camera hardware, the scanner's lifecycle, and potential errors. You can use this state to build reactive UIs that respond to camera changes, zoom levels, or permission issues.

Key properties include:

• isInitialized: Indicates if the scanner has successfully initialized (note: this is distinct from camera permission).
• isRunning: true if the camera is currently active.
• isStarting: true if the scanner is in the process of starting; use this to prevent duplicate calls to MobileScannerController.start().
• hasCameraPermission: A helper getter that returns true if the scanner is initialized and no permissionDenied error is present.
• cameraDirection: The current facing direction (CameraFacing).
• torchState: The current state of the flashlight (TorchState).
• zoomScale: The current zoom level.
• error: Contains a MobileScannerException if something went wrong.