Name: How to Implement a Flutter QR Code Scanner Plugin for iOS in Swift
Rating: 4.4 (39 reviews)
Author: yushulx

Previously, I wrote a blog post sharing how to implement a Flutter QR code scanner plugin for Android. For cross-platform mobile development, a plugin is not perfect if it does not support both Android and iOS. In this article, I am going to complement the iOS part of the plugin in order to bring the best development experience for mobile developers.

Flutter QR Code Scanner Plugin

https://pub.dev/packages/flutter_camera_qrcode_scanner

Dev Environment

M1 Mac
Xcode 13.2.1

Step-by-step Guide: Implement Flutter QR Code Scanner Plugin for iOS

Step 1: Get the Existing Flutter Plugin Project:

git clone https://github.com/yushulx/flutter_qrcode_scanner

Step 2: Add Support for iOS

cd flutter_qrcode_scanner
flutter create --template=plugin --platforms=ios .

Step 3: Install Dynamsoft Camera Enhancer and Dynamsoft Barcode Reader

Open iOS/flutter_camera_qrcode_scanner.podspec to add Dynamsoft Camera Enhancer 2.1.1 and Dynamsoft Barcode Reader 8.9.1:

s.dependency 'DynamsoftBarcodeReader', '8.9.1'
s.dependency 'DynamsoftCameraEnhancer', '2.1.1'

The dependencies will be installed via pod install.

Activating Mobile QR Code SDK

Click here to get a valid license key for Dynamsoft Barcode Reader.

Step 4: Implement the Factory and the Platform View Using Swift Code

Since we have completed the code logic on the Dart side, we only need to focus on the platform-related code. According to the official tutorial and the Android part of the plugin, we can write Swift code for iOS as follows:

Based on the structure of the Android QRCodeScanner class, we create a FLQRCodeScanner class in iOS/Classes/FLQRCodeScanner.swift:

import Flutter
import UIKit
import DynamsoftBarcodeReader
import DynamsoftCameraEnhancer

public protocol DetectionHandler {
        func onDetected(data: NSArray)
    }

class FLQRCodeScanner: NSObject, DBRTextResultDelegate {

    private var cameraView: DCECameraView
    private var dce: DynamsoftCameraEnhancer
    private var barcodeReader: DynamsoftBarcodeReader! = nil
    private var handler: DetectionHandler?

    init(cameraView: DCECameraView, dce: DynamsoftCameraEnhancer) {
        self.cameraView = cameraView
        self.cameraView.overlayVisible = true
        self.dce = dce
        super.init()

        createBarcodeReader(dce: dce)
    }

    func setDetectionHandler(handler: DetectionHandler) {
        self.handler = handler;
    }

    func createBarcodeReader(dce: DynamsoftCameraEnhancer) {
        // To activate the sdk, apply for a license key: https://www.dynamsoft.com/customer/license/trialLicense?product=dbr
        barcodeReader = DynamsoftBarcodeReader.init(license: "license-key")
        barcodeReader.setCameraEnhancer(dce)

        // Set text result call back to get barcode results.
        barcodeReader.setDBRTextResultDelegate(self, userData: nil)

        // Start the barcode decoding thread.
        barcodeReader.startScanning()
    }

    func textResultCallback(_ frameId: Int, results: [iTextResult]?, userData: NSObject?) {
        if results!.count > 0 {
            let outResults = NSMutableArray()
            for item in results! {
                let subDic = NSMutableDictionary()
                if item.barcodeFormat_2 != EnumBarcodeFormat2.Null {
                    subDic.setObject(item.barcodeFormatString_2 ?? "", forKey: "format" as NSCopying)
                }else{
                    subDic.setObject(item.barcodeFormatString ?? "", forKey: "format" as NSCopying)
                }
                subDic.setObject(item.barcodeText ?? "", forKey: "text" as NSCopying)
                let points = item.localizationResult?.resultPoints as! [CGPoint]
                subDic.setObject(Int(points[0].x), forKey: "x1" as NSCopying)
                subDic.setObject(Int(points[0].y), forKey: "y1" as NSCopying)
                subDic.setObject(Int(points[1].x), forKey: "x2" as NSCopying)
                subDic.setObject(Int(points[1].y), forKey: "y2" as NSCopying)
                subDic.setObject(Int(points[2].x), forKey: "x3" as NSCopying)
                subDic.setObject(Int(points[2].y), forKey: "y3" as NSCopying)
                subDic.setObject(Int(points[3].x), forKey: "x4" as NSCopying)
                subDic.setObject(Int(points[3].y), forKey: "y4" as NSCopying)
                subDic.setObject(item.localizationResult?.angle ?? 0, forKey: "angle" as NSCopying)
                outResults.add(subDic)
            }

            if handler != nil {
                handler!.onDetected(data: outResults)
            }
        }
    } 

    func startScan() {
        cameraView.overlayVisible = true
        barcodeReader.startScanning()
    }

    func stopScan() {
        cameraView.overlayVisible = false
        barcodeReader.stopScanning()
    }

    func setBarcodeFormats(arg:NSDictionary) {
        let formats:Int = arg.value(forKey: "formats") as! Int
        let settings = try! barcodeReader!.getRuntimeSettings()
        settings.barcodeFormatIds = formats
        barcodeReader!.update(settings, error: nil)
    }

    func setLicense(license: String) {
        barcodeReader.license = license
    }
}

Then we create a FLNativeView class in iOS/Classes/FLNativeView.swift to implement the camera view:

import Flutter
import UIKit
import DynamsoftCameraEnhancer

class FLNativeView: NSObject, FlutterPlatformView, DetectionHandler {
    private var _view: UIView
    private var messenger: FlutterBinaryMessenger
    private var channel: FlutterMethodChannel
    private var qrCodeScanner: FLQRCodeScanner
    init(
        frame: CGRect,
        viewIdentifier viewId: Int64,
        arguments args: Any?,
        binaryMessenger: FlutterBinaryMessenger
    ) {
        self.messenger = binaryMessenger
        let cameraView = DCECameraView.init(frame: frame)
        let dce = DynamsoftCameraEnhancer.init(view: cameraView)
        dce.open()
        dce.setFrameRate(30)
        _view = cameraView

        qrCodeScanner = FLQRCodeScanner.init(cameraView: cameraView, dce: dce)

        channel = FlutterMethodChannel(name: "com.dynamsoft.flutter_camera_qrcode_scanner/nativeview_" + String(viewId), binaryMessenger: messenger)

        super.init()

        qrCodeScanner.setDetectionHandler(handler: self)
        channel.setMethodCallHandler({
        (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
            switch call.method {
                case "startScanning":
                    self.qrCodeScanner.startScan()
                    result(.none)
                case "stopScanning":
                    self.qrCodeScanner.stopScan()
                    result(.none)
                case "setLicense":
                    self.qrCodeScanner.setLicense(license: (call.arguments as! NSDictionary).value(forKey: "license") as! String)
                    result(.none)
                case "setBarcodeFormats":
                    self.qrCodeScanner.setBarcodeFormats(arg: call.arguments as! NSDictionary)
                    result(.none)
                default:
                    result(.none)
                }
        })
    }

    func view() -> UIView {
        return _view
    }

    func onDetected(data: NSArray) {
        DispatchQueue.main.async {
                self.channel.invokeMethod("onDetected", arguments: data)
            }
    }
}

The native view contains a channel to handle Flutter method calls (from Dart to native). It also triggers the onDetected callback function (from native to Dart). When a QR code is detected, the channel will send the QR information from the native side to the Dart side .

Next, create a FLNativeViewFactory class in iOS/Classes/FLNativeViewFactory.swift to initialize the native view:

import Flutter
import UIKit

class FLNativeViewFactory: NSObject, FlutterPlatformViewFactory {
    private var messenger: FlutterBinaryMessenger

    init(messenger: FlutterBinaryMessenger) {
        self.messenger = messenger
        super.init()
    }

    func create(
        withFrame frame: CGRect,
        viewIdentifier viewId: Int64,
        arguments args: Any?
    ) -> FlutterPlatformView {
        return FLNativeView(
            frame: frame,
            viewIdentifier: viewId,
            arguments: args,
            binaryMessenger: messenger
        )
    }
}

The final step is to register the factory in iOS/Classes/SwiftFlutterCameraQrcodeScannerPlugin.swift:

import Flutter
import UIKit

public class SwiftFlutterCameraQrcodeScannerPlugin: NSObject, FlutterPlugin {
  public static func register(with registrar: FlutterPluginRegistrar) {  
    let factory = FLNativeViewFactory(messenger: registrar.messenger())
    registrar.register(factory, withId: "com.dynamsoft.flutter_camera_qrcode_scanner/nativeview")
  }
}

So far, the native Swift code for plugin is done.

Step 5: Test the QR code scanner in Flutter

Go to the example folder and add the camera access permission to ios/Runner/Info.plist:

<key>NSCameraUsageDescription</key>
<string>Can I use the camera please?</string>
<key>NSMicrophoneUsageDescription</key>
<string>Can I use the mic please?</string>

Run the example on iOS devices:
```
flutter run
```

Source Code

https://github.com/yushulx/flutter_qrcode_scanner