Example of a custom react-native component, written in swift. Original author @euforic

BarcodeScanner.swift

//  Barcode.swift
 
import UIKit;
import AVFoundation;
 
@objc(BarcodeScanner)
public class BarcodeScanner: UIView, AVCaptureMetadataOutputObjectsDelegate {
  
  let session         : AVCaptureSession = AVCaptureSession()
  var previewLayer    : AVCaptureVideoPreviewLayer!
  var highlightView   : UIView = UIView()
  var bridge          : RCTEventDispatcher!
  var enabled         : Bool {
    set(newValue) {
      println("Setting isScanning to:", newValue)
      if newValue {
        self.startScanner();
        return
      }
      self.stopScanner();
    }
    get {
      return self.session.running;
    }
  }
  
  override init(frame: CGRect) {
    super.init(frame: frame)
  }
  
  required public init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
  }
  
  public func initWithEventDispatcher(bridge: RCTEventDispatcher) -> UIView {
    self.bridge = bridge;
    // Select the color you want for the completed scan reticle
    self.highlightView.layer.borderColor = UIColor.greenColor().CGColor
    self.highlightView.layer.borderWidth = 3
    
    // Add it to our controller's view as a subview.
    self.addSubview(self.highlightView)
    
    
    // For the sake of discussion this is the camera
    let device = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    
    // Create a nilable NSError to hand off to the next method.
    // Make sure to use the "var" keyword and not "let"
    var error : NSError? = nil
    
    
    let input : AVCaptureDeviceInput? = AVCaptureDeviceInput.deviceInputWithDevice(device, error: &error) as? AVCaptureDeviceInput
    
    // If our input is not nil then add it to the session, otherwise we're kind of done!
    if input != nil {
      session.addInput(input)
    }
    else {
      // This is fine for a demo, do something real with this in your app. :)
      println(error)
    }
    
    let output = AVCaptureMetadataOutput()
    output.setMetadataObjectsDelegate(self, queue: dispatch_get_main_queue())
    session.addOutput(output)
    output.metadataObjectTypes = output.availableMetadataObjectTypes
    
    
    previewLayer = AVCaptureVideoPreviewLayer.layerWithSession(session) as! AVCaptureVideoPreviewLayer
    previewLayer.frame = self.bounds
    previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
    self.layer.addSublayer(previewLayer)
    
    return self;
  }
 
  
  
  
  @objc public func startScanner() {
    if !self.session.running {
      self.session.startRunning();
    }
  }
  
  @objc public func stopScanner() {
    if self.session.running {
      self.session.stopRunning();
    }
  }
  
  override public func layoutSubviews() {
    self.previewLayer.frame = self.bounds
    if !self.session.running {
      self.session.startRunning()
    }
  }
  
  // This is called when we find a known barcode type with the camera.
  public func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {
    
    var highlightViewRect = CGRectZero
    
    var barCodeObject : AVMetadataObject!
    
    var detectionString : String!
    
    let barCodeTypes = [AVMetadataObjectTypeUPCECode,
      AVMetadataObjectTypeCode39Code,
      AVMetadataObjectTypeCode39Mod43Code,
      AVMetadataObjectTypeEAN13Code,
      AVMetadataObjectTypeEAN8Code,
      AVMetadataObjectTypeCode93Code,
      AVMetadataObjectTypeCode128Code,
      AVMetadataObjectTypePDF417Code,
      AVMetadataObjectTypeQRCode,
      AVMetadataObjectTypeAztecCode
    ]
    
    
    // The scanner is capable of capturing multiple 2-dimensional barcodes in one scan.
    for metadata in metadataObjects {
      
      for barcodeType in barCodeTypes {
        
        if metadata.type == barcodeType {
          barCodeObject = self.previewLayer.transformedMetadataObjectForMetadataObject(metadata as! AVMetadataMachineReadableCodeObject)
          
          highlightViewRect = barCodeObject.bounds
          
          detectionString = (metadata as! AVMetadataMachineReadableCodeObject).stringValue
          
          self.session.stopRunning()
          break
        }
        
      }
    }
    if detectionString != nil {
      self.bridge.sendDeviceEventWithName("capture", body: detectionString);
    }
    self.highlightView.frame = highlightViewRect
    self.bringSubviewToFront(self.highlightView)
    
  }
}

BarcodeScannerViewManager.h

//  BarcodeViewManager.h
 
#import "RCTViewManager.h"
#import "RCTBridgeModule.h"
 
@interface BarcodeScannerViewManager: RCTViewManager
 
@end

BarcodeScannerViewManager.m

//  BarcodeViewManager.m
 
#import "BarcodeScannerViewManager.h"
#import "techtime-Swift.h"
#import "RCTEventDispatcher.h"
#import "RCTBridge.h"
#import "RCTBridgeModule.h"
 
@implementation BarcodeScannerViewManager
@synthesize bridge = _bridge;
 
RCT_EXPORT_MODULE();
 
- (UIView *)view {
  return [[[BarcodeScanner alloc] init ] initWithEventDispatcher:_bridge.eventDispatcher];
}
 
RCT_EXPORT_VIEW_PROPERTY(enabled, BOOL);
 
@end

bridge-hader.h

//
//  Use this file to import your target's public headers that you would like to expose to Swift.
//
#import "RCTView.h"
#import "RCTViewManager.h"
#import "RCTBridge.h"
#import "RCTEventDispatcher.h"
#import "RCTUtils.h"
#import "UIView+React.h"
#import "RCTLog.h"