QR (short for Quick Response) code. QR code has gained popularity in consumer space in recent years as a way to encode URL of a landing page or marketing information. Unlike the basic barcode that we’re familiar with QR code contains information in both horizontal and vertical direction. Thus this contributes to its capability of storing larger amount of data in both numeric and letter form.In this tutorial we will build a similar QR code reader app in Swift. After going through the tutorial you will understand how to use the AVFoundation framework to discover and read QR code in real-time. Any barcode scanning in iOS including QR code is totally based on video capturing. That’s why the barcode scanning feature is added in the AVFoundation framework.The app works pretty much like a video capturing app but without recording feature. When the app is launched it takes advantage of the iPhone’s rear camera to spot the QR code and recognises it automatically.
I have created the user interface of the app in the project template. The label in the UI will be used to display decoded information of QR code and it is associated with the msglbl property of the ViewController class.
As mentioned we rely on the AVFoundation framework to implement the QR code scanning feature.
1) First, open ViewController.swift and import the framework:
import AVFoundation
2) Later, we’ll need to implement the AVCaptureMetadataOutputObjectsDelegate protocol.
class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate
3) Instantiate an AVCaptureSession object with the input set to the appropriate AVCaptureDevice for video capturing. Since we are going to capture video data we call the default(for:) method passing it AVMediaTypeVideo to get the video capture device. We instantiate an AVCaptureSession object and add the input of the video capture device. The AVCaptureSession object is used to coordinate the flow of data from the video input device to our output.
The output of the session is set to an AVCaptureMetaDataOutput object. The AVCaptureMetaDataOutput class is the core part of QR code reading.
This class in combination with the AVCaptureMetadataOutputObjectsDelegate protocol is used to intercept any metadata found in the input device (the QR code captured by the device’s camera) and translate it to a human-readable format.
4) The metadataObjectTypes property is also quite important as this is the point where we tell the app what kind of metadata we are interested in. The AVMetadataObjectTypeQRCode clearly indicates our purpose.We have set and configured an AVCaptureMetadataOutput object we need to display the video captured by the device’s camera on screen. This can be done using an AVCaptureVideoPreviewLayer which actually is a CALayer. You use this preview layer in conjunction with an AV capture session to display video. The preview layer is added as a sublayer of the current view. Start the video capture by calling the startRunning method of the capture session.
5) When the AVCaptureMetadataOutput object recognises a QR code the following delegate method of AVCaptureMetadataOutputObjectsDelegate will be called:
func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection)
The second parameter (i.e. metadataObjects) of the method is an array object which contains all the metadata objects that have been read.
6) Lastly we decode the QR code into human-readable information.The decoded information can be accessed by using the stringValue property of an AVMetadataMachineReadableCode object.iOS requires app developers to obtain the user’s permission before allowing to access the camera. To do so you have to add a key named NSCameraUsageDescription in the Info.plist file. Open the file and Set the key to Privacy – Camera Usage Description and value to We need to access your camera for scanning QR code.
7) Now you’re ready to go! Hit the Run button to compile and run the app on a real device. Once launched tap the scan button and then point the device to the QR code.The app immediately detects the code and decodes the information.
You can download the completed project here
