Advanced Configurations
Customization of the Overlays
Basic Overlay
To customize the appearance of an overlay you can implement a ILabelCaptureBasicOverlayListener and/or ILabelCaptureAdvancedOverlayListener 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.
public class BasicOverlayListener : ILabelCaptureBasicOverlayListener
{
/*
* Customize the appearance of the overlay for the individual fields.
*/
public Brush BrushForField(
LabelCaptureBasicOverlay overlay,
CapturedField field,
CapturedLabel label)
{
return field.Name switch
{
"<your-barcode-field-name>" => new Brush(
Color.Cyan.WithAlpha(128),
Color.Cyan,
1f
),
"<your-expiry-date-field-name>" => new Brush(
Color.Green.WithAlpha(128),
Color.Green,
1f
),
_ => new Brush(Color.Transparent, Color.Transparent, 0f)
};
}
/*
* Customize the appearance of the overlay for the full label.
* In this example, we disable label overlays by returning null always.
*/
public Brush BrushForLabel(
LabelCaptureBasicOverlay overlay,
CapturedLabel label)
{
return null;
}
public void OnLabelTapped(
LabelCaptureBasicOverlay overlay,
CapturedLabel label)
{
/*
* Handle the user tap gesture on the label.
*/
}
}
// Set the listener on the overlay
overlay.Listener = new BasicOverlayListener();
tip
You can also use LabelCaptureBasicOverlay.SetLabelBrush() and LabelCaptureBasicOverlay.SetCapturedFieldBrush() 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 an advanced overlay that allows for custom views to be added over detected label fields
// This is the key component for implementing Augmented Reality features
var advancedOverlay = LabelCaptureAdvancedOverlay.Create(labelCapture, dataCaptureView);
// Configure the advanced overlay with a listener that handles AR content creation and positioning
advancedOverlay.Listener = new AdvancedOverlayListener(this);
public class AdvancedOverlayListener : ILabelCaptureAdvancedOverlayListener
{
private readonly Context context;
public AdvancedOverlayListener(Context context)
{
this.context = context;
}
// This method is called when a label is detected - we return null since we're only adding AR elements to specific fields, not the entire label
public View ViewForCapturedLabel(
LabelCaptureAdvancedOverlay overlay,
CapturedLabel capturedLabel)
{
return null;
}
// This defines where on the detected label the AR view would be anchored
public Anchor AnchorForCapturedLabel(
LabelCaptureAdvancedOverlay overlay,
CapturedLabel capturedLabel)
{
return Anchor.Center;
}
// This defines the offset from the anchor point for the label's AR view
public PointWithUnit OffsetForCapturedLabel(
LabelCaptureAdvancedOverlay overlay,
CapturedLabel capturedLabel,
View view)
{
return new PointWithUnit(0f, 0f, MeasureUnit.Pixel);
}
// This method is called when a field is detected in a label
public View ViewForCapturedLabelField(
LabelCaptureAdvancedOverlay overlay,
LabelField labelField)
{
// We only want to create AR elements for expiry date fields that are text-based
if (labelField.Name.ToLower().Contains("expiry") && labelField.Type == LabelFieldType.Text)
{
//
// data extraction from expiry date field and days until expiry date calculation
//
// Check if scanned expiry date is too close to actual date
var daysUntilExpiry = CalculateDaysUntilExpiry(labelField.Text);
var dayLimit = 3;
if (daysUntilExpiry < dayLimit)
{
// Create and configure the AR element - a TextView with appropriate styling
// This view will appear as an overlay on the camera feed
var textView = new TextView(context)
{
Text = "Item expires soon!",
TextSize = 14f
};
textView.SetTextColor(Color.White);
textView.SetBackgroundColor(Color.Red);
textView.SetPadding(16, 8, 16, 8);
// Add an icon to the left of the text for visual guidance
// This enhances the AR experience by providing clear visual cues
var drawable = ContextCompat.GetDrawable(context, Resource.Drawable.ic_warning);
if (drawable != null)
{
drawable.SetBounds(0, 0, drawable.IntrinsicWidth, drawable.IntrinsicHeight);
textView.SetCompoundDrawables(drawable, null, null, null);
}
textView.CompoundDrawablePadding = 16; // Add some padding between icon and text
return textView;
}
}
// Return null for any fields that aren't expiry dates, which means no AR overlay
return null;
}
// This defines where on the detected field the AR view should be anchored
// BottomCenter places it right below the expiry date text for better visibility
public Anchor AnchorForCapturedLabelField(
LabelCaptureAdvancedOverlay overlay,
LabelField labelField)
{
return Anchor.BottomCenter;
}
// This defines the offset from the anchor point
public PointWithUnit OffsetForCapturedLabelField(
LabelCaptureAdvancedOverlay overlay,
LabelField labelField,
View view)
{
return new PointWithUnit(0f, 22f, MeasureUnit.Dip);
}
private int CalculateDaysUntilExpiry(string expiryDateText)
{
// Parse the expiry date and calculate days remaining
// Implementation depends on your date format
return 0; // placeholder
}
}
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 overlay
var validationFlowOverlay = LabelCaptureValidationFlowOverlay.Create(
context,
labelCapture,
dataCaptureView
);
// Set the listener to receive validation events
validationFlowOverlay.Listener = new ValidationFlowListener();
Adjust the Hint Messages
// Configure the validation flow with custom settings
var validationSettings = LabelCaptureValidationFlowSettings.Create();
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 of this string
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 ILabelCaptureValidationFlowOverlayListener interface.
public class ValidationFlowListener : ILabelCaptureValidationFlowOverlayListener
{
// This is called by the validation flow overlay when a label has been fully captured and validated
public void OnValidationFlowLabelCaptured(IList<LabelField> fields)
{
string barcodeData = null;
string expiryDate = null;
foreach (var field in fields)
{
if (field.Name == "<your-barcode-field-name>")
{
barcodeData = field.Barcode?.Data;
}
else if (field.Name == "<your-expiry-date-field-name>")
{
expiryDate = field.Text;
}
}
// Process the captured and validated data
}
}