A Flutter Plugin to Add Read/Scan QR Code Functionality in Your Flutter App

QR Mobile Vision

Reading QR codes and other barcodes using Firebase’s MLKit.

This plugin uses Android & iOS native APIs for reading images from the device’s camera. It then pipes these images both to the MLKit Vision Barcode API which detects barcodes/qrcodes etc, and outputs a preview image to be shown on a flutter texture.

The plugin includes a widget which performs all needed transformations on the camera output to show within the defined area.

This has been tested on the following devices(emulators):

• Nexus 5x
• Nexus 4
• Pixel 3a
• iPhone 7

Android Models

With this new version of MLKit, there are two seperate models you can use to do the barcode scanning. Currently, this apk chooses to use the build-in model. This will increase your code size by ~2.2MB but will result in better scanning and won’t require a seperate package to be downloaded in the background for barcode scanning to work properly.

You could also use the Google Play Services and tell your app to download it on install from the play store. See the instruction on the ml-kit barcode-scanning documentation page for android. You would also have to remove the com.google.mlkit:barcode-scanning dependency; this hasn’t been tested but would probably go something like this:

configurations.all {
    exclude group: "com.google.mlkit", module:"barcode-scanning"
}
//  ...
dependencies {
  // ...
  // Use this dependency to use the dynamically downloaded model in Google Play Services
  implementation 'com.google.android.gms:play-services-mlkit-barcode-scanning:16.1.4'
}

Note that if you do this, you should tell your app to automatically download the model as in the above linked docs.MLKit

<application ...>
    ...
    <meta-data
        android:name="com.google.mlkit.vision.DEPENDENCIES"
        android:value="barcode" />
    <!-- To use multiple models: android:value="barcode,model2,model3" -->
</application>

If this doesn’t work for you please open an issue.

64 Bit Only on iOS

Unfortunately, Google has only released MLKit as a 64 bit binary. That means that this plugin and therefore your app don’t support building or running on 32 bit. There were two possible approaches to dealing with this, but only one made it so that most users will be able to use the plugin easily.app

When you upgrade, if you are targeting a version of iOS before 11, you’ll see a warning during the pod install and your app probably won’t build (at least for release). That’s because it’ll be trying to build the 32-bit version and won’t find the required files.

The easy way to solve this is by updating to build for iOS 11 and later. To do this:

1. Add this line to your Podfile:

platform :ios, '11.0'

2. (optional) Make sure your podfile sets build versions to 11 – if you see this at the bottom of your podfile make sure the line setting the deployment target to 11 is in there.

post_install do |installer|
    installer.pods_project.targets.each do |target|
        target.build_configurations.each do |config|
            config.build_settings['ENABLE_BITCODE'] = 'NO'
            config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '11.0'
        end
    end
end

3. Setting the iOS Deployment Target to 11 in XCode -> Runner -> Build Settings -> Deployment -> iOS Deployment Target.

Building for 64-bit before 11.0.

If you absolutely need to build for devices before 11.0, you might need to use an old version of the library that supports 32-bit. If you’re willing to live without 32 bit but do need to target before 11.0, you can do that by ignoring the warning CocoaPods will give you, and setting XCode -> Runner -> Build Settings -> Architectures -> Architectures to ${ARCHS_STANDARD_64_BIT}.

Usage

See the example for how to use this plugin; it is the best resource available as it shows the plugin in use. However, these are the steps you need to take to use this plugin.

First, figure out the area that you want the camera preview to be shown in. This is important as the preview needs to have a constrained size or it won’t be able to build. This is required due to the complex nature of the transforms needed to get the camera preview to show correctly on both iOS and Android, while still working with the screen rotated etc.

It may be possible to get the camera preview to work without putting it in a SizedBox or Container, but the recommended way is to put it in a SizedBox or Container.

You then need to include the package and instantiate the camera.

import 'package:qr_mobile_vision/qr_camera.dart';

...

new SizedBox(
  width: 300.0,
  height: 600.0,
  child: new QrCamera(
    qrCodeCallback: (code) {
      ...
    },
  ),
)

The QrCodeCallback can do anything you’d like, and wil keep receiving QR codes until the camera is stopped.

There are also optional parameters to QrCamera.

fit

Takes as parameter the flutter BoxFit. Setting this to different values should get the preview image to fit in different ways, but only BoxFit = cover has been tested extensively.

notStartedBuilder

A callback that must return a widget if defined. This should build whatever you want to show up while the camera is loading (which can take from milliseconds to seconds depending on the device).

child

Widget that is shown on top of the QrCamera. If you give it a specific size it may cause weird issues so try not to.

key

Standard flutter key argument. Can be used to get QrCameraState with a GlobalKey.

offscreenBuilder

A callback that must return a widget if defined. This should build whatever you want to show up when the camera view is ‘offscreen’. i.e. when the app is paused. May or may not show up in preview of app.

onError

Callback for if there’s an error.

formats

A list of supported formats, all by default. If you use all, you shouldn’t define any others.

These are the supported types:

  ALL_FORMATS,
  AZTEC,
  CODE_128,
  CODE_39,
  CODE_93,
  CODABAR,
  DATA_MATRIX,
  EAN_13,
  EAN_8,
  ITF,
  PDF417,
  QR_CODE,
  UPC_A,
  UPC_E

Push and Pop

If you push a new widget on top of a the current page using the navigator, the camera doesn’t necessarily know about it.

Contributions

Anyone wanting to contribute to this project is very welcome to! I’ll take a look at PR’s as soon as I can, and any bug reports are appreciated. I’ve only a few devices on which to test this so feedback about other devices is appreciated as well.

GitHub

Source Code: flutter qr mobile vision.