Advanced Configurations

Customization of the Overlays

To customize the appearance of an overlay you can implement a LabelCaptureBasicOverlayListener and/or LabelCaptureAdvancedOverlayListener interface, depending on the overlay(s) you are using.

The method brushForLabel() is called every time a label is captured, and brushForField() is called for each of its fields to determine the brush for the label or field.

// Create a custom listener class that implements LabelCaptureBasicOverlayListener.
class MyBasicOverlayListener implements LabelCaptureBasicOverlayListener {
  @override
  Future<Brush?> brushForLabel(LabelCaptureBasicOverlay overlay, CapturedLabel label) async {
    // Return null to use the default brush for the label.
    return null;
  }

  @override
  Future<Brush?> brushForFieldOfLabel(
      LabelCaptureBasicOverlay overlay, LabelField field, CapturedLabel label) async {
    if (field.name == 'Barcode') {
      // Highlight barcode fields with a cyan color.
      return Brush(
        Color.fromRGBO(0, 255, 255, 0.5),
        Color.fromRGBO(0, 255, 255, 0.5),
        0,
      );
    }

    if (field.name == 'Expiry Date') {
      // Highlight expiry date fields with an orange color.
      return Brush(
        Color.fromRGBO(255, 165, 0, 0.5),
        Color.fromRGBO(255, 165, 0, 0.5),
        0,
      );
    }

    // Return null to use the default brush for other fields.
    return null;
  }

  @override
  void didTapLabel(LabelCaptureBasicOverlay overlay, CapturedLabel label) {
    // Handle user tap gestures on the label.
  }
}

// Set the listener on the overlay.
overlay.listener = MyBasicOverlayListener();

tip

You can also use the labelBrush and capturedFieldBrush properties on LabelCaptureBasicOverlay to configure the overlay if you don't need to customize the appearance based on the name or content of the fields.

Advanced Overlay

For more advanced use cases, such as adding custom views or implementing Augmented Reality (AR) features, you can use the LabelCaptureAdvancedOverlay. The example below creates an advanced overlay, configuring it to display a styled warning message below expiry date fields when they’re close to expiring, while ignoring other fields.

// Create the advanced overlay.
final advancedOverlay = LabelCaptureAdvancedOverlay.newInstance(
  labelCapture,
  dataCaptureView,
);

// Create a custom listener class that implements LabelCaptureAdvancedOverlayListener.
class MyAdvancedOverlayListener implements LabelCaptureAdvancedOverlayListener {
  @override
  Widget? viewForCapturedLabel(LabelCaptureAdvancedOverlay overlay, CapturedLabel label) {
    return null; // We only care about specific fields.
  }

  @override
  Anchor anchorForCapturedLabel(LabelCaptureAdvancedOverlay overlay, CapturedLabel label) {
    return Anchor.center;
  }

  @override
  PointWithUnit offsetForCapturedLabel(
      LabelCaptureAdvancedOverlay overlay, CapturedLabel label, Widget? view) {
    return PointWithUnit(0, 0, MeasureUnit.pixel);
  }

  @override
  Widget? viewForCapturedLabelField(LabelCaptureAdvancedOverlay overlay, LabelField field) {
    if (field.name.toLowerCase().contains('expiry') && field.type == LabelFieldType.text) {
      // Your method to calculate days until expiry.
      final daysUntilExpiry = calculateDaysUntilExpiry(field.text);
      const dayLimit = 3;

      if (daysUntilExpiry < dayLimit) {
        return Container(
          padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
          color: Colors.red,
          child: Row(
            mainAxisSize: MainAxisSize.min,
            children: const [
              Icon(Icons.warning, color: Colors.white),
              SizedBox(width: 8),
              Text('Item expires soon!', style: TextStyle(color: Colors.white)),
            ],
          ),
        );
      }
    }
    return null;
  }

  @override
  Anchor anchorForCapturedLabelField(LabelCaptureAdvancedOverlay overlay, LabelField field) {
    return Anchor.bottomCenter;
  }

  @override
  PointWithUnit offsetForCapturedLabelField(
      LabelCaptureAdvancedOverlay overlay, LabelField field, Widget? view) {
    return PointWithUnit(0, 22, MeasureUnit.dip);
  }
}

// Set the listener on the advanced overlay.
advancedOverlay.listener = MyAdvancedOverlayListener();

Validation Flow

Implementing a validation flow in your Smart Label Capture application differs from the Get Started steps outlined earlier as follows:

Visualize the Scan Process

Validation flow uses a different overlay, the LabelCaptureValidationFlowOverlay. This overlay provides a user interface that guides users through the label capture process, including validation steps.

// Create the validation flow overlay.
final validationFlowOverlay = LabelCaptureValidationFlowOverlay.newInstance(
  dataCaptureContext,
  labelCapture,
  dataCaptureView,
);

// Set the listener.
validationFlowOverlay.listener = MyValidationFlowListener();

Adjust the Hint Messages

// Create and configure validation flow settings.
final validationSettings = LabelCaptureValidationFlowSettings();

validationSettings.missingFieldsHintText = 'Please add this field';
validationSettings.standbyHintText = 'No label detected, camera paused';
validationSettings.validationHintText = 'fields captured'; // X/Y (X fields out of total Y) is shown in front
validationSettings.validationErrorText = 'Input not valid';
validationSettings.requiredFieldErrorText = 'This field is required';
validationSettings.manualInputButtonText = 'Add info manually';

// Apply the settings to the overlay.
validationFlowOverlay.applySettings(validationSettings);

Define a Listener

To handle validation events, implement the LabelCaptureValidationFlowOverlayListener interface.

// Create a custom listener class that implements LabelCaptureValidationFlowOverlayListener.
class MyValidationFlowListener implements LabelCaptureValidationFlowOverlayListener {
  @override
  void didCompleteLabelCapture(List<LabelField> fields) {
    String? barcodeData;
    String? expiryDate;

    for (final field in fields) {
      if (field.name == 'Barcode') {
        barcodeData = field.barcode?.data;
      } else if (field.name == 'Expiry Date') {
        expiryDate = field.text;
      }
    }

    // Handle the captured values.
    print('Barcode: $barcodeData, Expiry: $expiryDate');
  }
}