CAMERA_SELECTION.md

Camera Selection Feature

The camera selection feature allows you to enumerate available cameras on a device and select a specific camera to use for barcode scanning or camera preview.

Overview

This feature is useful in scenarios where:

• A device has multiple cameras (e.g., front, rear, external webcams on desktop)
• You want to give users control over which camera to use
• You need to remember and restore a user's camera preference
• You want to support external cameras on desktop platforms

API Reference

CameraInfo Class

Represents metadata about an available camera.

public class CameraInfo
{
    public string DeviceId { get; set; }    // Unique identifier for the camera
    public string Name { get; set; }         // Human-readable name of the camera
    public CameraLocation Location { get; set; }  // Front or Rear
}

GetAvailableCameras Method

Returns a list of all available cameras on the device.

public async Task<IReadOnlyList<CameraInfo>> GetAvailableCameras()

Available on both CameraView and CameraBarcodeReaderView controls.

SelectedCamera Property

Sets or gets the currently selected camera.

public CameraInfo SelectedCamera { get; set; }

When set to null, the default camera for the specified CameraLocation is used.

Usage Examples

Example 1: List Available Cameras

var cameras = await cameraBarcodeReaderView.GetAvailableCameras();

foreach (var camera in cameras)
{
    Console.WriteLine($"Camera: {camera.Name}");
    Console.WriteLine($"  ID: {camera.DeviceId}");
    Console.WriteLine($"  Location: {camera.Location}");
}

Example 2: Select a Specific Camera

var cameras = await cameraBarcodeReaderView.GetAvailableCameras();

// Select the first rear camera
var rearCamera = cameras.FirstOrDefault(c => c.Location == CameraLocation.Rear);
if (rearCamera != null)
{
    cameraBarcodeReaderView.SelectedCamera = rearCamera;
}

Example 3: User Camera Selection UI

async void SelectCameraButton_Clicked(object sender, EventArgs e)
{
    var cameras = await cameraBarcodeReaderView.GetAvailableCameras();
    
    if (cameras.Count == 0)
    {
        await DisplayAlert("No Cameras", "No cameras found.", "OK");
        return;
    }

    // Show action sheet to select camera
    var cameraNames = cameras.Select(c => c.Name).ToArray();
    var selectedName = await DisplayActionSheet("Select Camera", "Cancel", null, cameraNames);
    
    if (selectedName != null && selectedName != "Cancel")
    {
        var selectedCamera = cameras.FirstOrDefault(c => c.Name == selectedName);
        if (selectedCamera != null)
        {
            cameraBarcodeReaderView.SelectedCamera = selectedCamera;
        }
    }
}

Example 4: Save and Restore Camera Preference

// Save camera preference
var selectedCamera = cameraBarcodeReaderView.SelectedCamera;
if (selectedCamera != null)
{
    Preferences.Set("PreferredCameraId", selectedCamera.DeviceId);
}

// Restore camera preference
var cameras = await cameraBarcodeReaderView.GetAvailableCameras();
var preferredCameraId = Preferences.Get("PreferredCameraId", string.Empty);

var camera = cameras.FirstOrDefault(c => c.DeviceId == preferredCameraId);
if (camera != null)
{
    cameraBarcodeReaderView.SelectedCamera = camera;
}

Example 5: XAML Binding

<zxing:CameraBarcodeReaderView
    x:Name="barcodeView"
    SelectedCamera="{Binding SelectedCamera}"
    BarcodesDetected="BarcodesDetected" />

public class MainViewModel : INotifyPropertyChanged
{
    private CameraInfo _selectedCamera;
    
    public CameraInfo SelectedCamera
    {
        get => _selectedCamera;
        set
        {
            _selectedCamera = value;
            OnPropertyChanged();
        }
    }
    
    public async Task LoadCamerasAsync()
    {
        var cameras = await barcodeView.GetAvailableCameras();
        // Select first camera
        if (cameras.Count > 0)
        {
            SelectedCamera = cameras[0];
        }
    }
}

Platform-Specific Notes

Android

• Uses AndroidX CameraX API to enumerate cameras
• Camera IDs are stable identifiers based on lens facing and enumeration order (e.g., "front-0", "rear-0", "rear-1")
• Camera names are descriptive (e.g., "Front Camera", "Rear Camera", "Rear Camera 2")
• All available cameras are returned, including external cameras
• Properly handles devices with multiple cameras of the same facing direction

iOS/MacCatalyst

• Uses AVFoundation framework to enumerate cameras
• Camera names are taken from the device's localized name
• Supports built-in cameras and external cameras (on MacCatalyst)

Windows

• Uses Windows MediaCapture and MediaFrameSourceGroup APIs
• Camera names are taken from device information
• Excellent support for multiple external cameras (webcams)
• Especially useful for desktop applications

Other Platforms

• Returns an empty list if camera enumeration is not supported

Important Notes

1. Permission Required: Camera permission must be granted before calling GetAvailableCameras().

2. Timing: Call GetAvailableCameras() after the camera view is initialized and connected.

3. Dynamic Changes: On Windows, cameras can be connected/disconnected dynamically. Consider refreshing the camera list when needed.

4. Default Behavior: When SelectedCamera is null, the view uses the default camera for the specified CameraLocation (Front or Rear).

5. Compatibility: Setting SelectedCamera takes precedence over CameraLocation. If you want to use CameraLocation again, set SelectedCamera to null.

Migration Guide

If you were using only CameraLocation before:

// Old way (still works)
cameraBarcodeReaderView.CameraLocation = CameraLocation.Front;

// New way (more control)
var cameras = await cameraBarcodeReaderView.GetAvailableCameras();
var frontCamera = cameras.FirstOrDefault(c => c.Location == CameraLocation.Front);
if (frontCamera != null)
{
    cameraBarcodeReaderView.SelectedCamera = frontCamera;
}

// To go back to automatic selection
cameraBarcodeReaderView.SelectedCamera = null;
cameraBarcodeReaderView.CameraLocation = CameraLocation.Rear;

Both approaches work and can be used interchangeably based on your needs.