CameraX小试牛刀，实现二维码扫描

在今年的Google I/O大会上，Google新推出了CameraX支持包，按照官方的说法, 这个包的作用是

help you make camera app development easier

google在几年前推出了Camera2 API用于取代Camera1，但是因为api太难用，大部分开发者还是喜欢使用Camera1的api，这不得不说是一件讽刺的事情。这次推出的CameraX支持包不仅消除各种使用上的障碍，还与大受好评的archecture component 包的Lifecycle结合，自动管理相机的生命周期，开发者不在需要去关心什么时候打开相机，什么时候释放相机。甚至联系各个手机厂商提供统一的api调用使用美颜等接口，看起来诚意满满。

本文将在这个demo中将会使用到CameraX中三大功能中的两个：

preview
analysis

创建app

创建app，声明相机权限

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:tools="http://schemas.android.com/tools" package="github.hotstu.camerax.qrcodec">

    <uses-permission android:name="android.permission.CAMERA"/>

    <application
            android:allowBackup="true"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme" tools:ignore="GoogleAppIndexingWarning">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
    </application>

</manifest>

添加相关依赖

    implementation 'com.tbruyelle.rxpermissions2:rxpermissions:0.9.5'
    def camerax_version = "1.0.0-alpha02"
    implementation "androidx.camera:camera-core:${camerax_version}"
    // If you want to use Camera2 extensions.
    implementation "androidx.camera:camera-camera2:${camerax_version}"
    implementation 'com.google.zxing:core:3.3.2'

注意，这里有个坑，因为camerax还没有发布正式版，而它依赖的androidx.core:core:1.1.0-rc1中AppcompatActivity居然不是LifeCycleOwner,所以要祭出在support liabary时代解决依赖冲突的黄金代码:

subprojects {
    configurations.all {
        resolutionStrategy {
            force "androidx.core:core:1.0.2"
        }
    }
}

编写代码实现摄像头预览

        val previewConfig = PreviewConfig.Builder().apply {
            setTargetAspectRatio(Rational(1, 1))
            setTargetResolution(Size(640, 640))
        }.build()
        val preview = Preview(previewConfig)
       preview.setOnPreviewOutputUpdateListener {
            textureView.surfaceTexture = it.surfaceTexture
        }
        CameraX.bindToLifecycle(this@MainActivity, preview)

编写代码实现数据分析回调

数据分析可以指定回调的线程

        val analysisConfig = ImageAnalysisConfig.Builder().apply {
            setImageReaderMode(ImageAnalysis.ImageReaderMode.ACQUIRE_LATEST_IMAGE)
            val analyzerThread = HandlerThread("BarcodeAnalyzer").apply { start() }
            setCallbackHandler(Handler(analyzerThread.looper))
        }.build()

        val analysis = ImageAnalysis(analysisConfig)
        analysis.analyzer = QRcodeAnalyzer()

        CameraX.bindToLifecycle(this@MainActivity, analysis)

同时绑定预览和分析，并且搞定权限申请

class MainActivity : AppCompatActivity() {

    @SuppressLint("CheckResult")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val previewConfig = PreviewConfig.Builder().apply {
            setTargetAspectRatio(Rational(1, 1))
            setTargetResolution(Size(640, 640))
        }.build()

        val analysisConfig = ImageAnalysisConfig.Builder().apply {
            setImageReaderMode(ImageAnalysis.ImageReaderMode.ACQUIRE_LATEST_IMAGE)
            val analyzerThread = HandlerThread("BarcodeAnalyzer").apply { start() }
            setCallbackHandler(Handler(analyzerThread.looper))
        }.build()

        val rxPermissions = RxPermissions(this)
        val preview = Preview(previewConfig)
        val analysis = ImageAnalysis(analysisConfig)

        preview.setOnPreviewOutputUpdateListener {
            textureView.surfaceTexture = it.surfaceTexture
        }

        analysis.analyzer = QRcodeAnalyzer()
        rxPermissions.request(android.Manifest.permission.CAMERA)
                .subscribe {
                    CameraX.bindToLifecycle(this@MainActivity,
                            preview,
                            analysis)
                }
    }
}

实现QRcodeAnalyzer

做二维码解码，很多开发者是直接在zxing-Android 项目基础上删删改改，其实不建议这样做，应为那个项目是从Android早期版本开始的，一些东西都为了支持老版本系统而做出了妥协，很多代码都显得老旧而且不优雅，查看源码你会发现它调用摄像头的方法是非常复杂的。这里我们只是用xzing核心库com.google.zxing:core

class QRcodeAnalyzer : ImageAnalysis.Analyzer {
    private val reader: MultiFormatReader = MultiFormatReader()

    init {
        val map = mapOf<DecodeHintType, Collection<BarcodeFormat>>(
            Pair(DecodeHintType.POSSIBLE_FORMATS, arrayListOf(BarcodeFormat.QR_CODE))
        )
        reader.setHints(map)
    }

    override fun analyze(image: ImageProxy, rotationDegrees: Int) {
        if (ImageFormat.YUV_420_888 != image.format) {
            Log.e("BarcodeAnalyzer", "expect YUV_420_888, now = ${image.format}")
            return
        }
        val buffer = image.planes[0].buffer
        val data = ByteArray(buffer.remaining())
        val height = image.height
        val width = image.width
        buffer.get(data)
        //TODO 调整crop的矩形区域，目前是全屏（全屏有更好的识别体验，但是在部分手机上可能OOM）
        val source = PlanarYUVLuminanceSource(data, width, height, 0, 0, width, height, false)

        val bitmap = BinaryBitmap(HybridBinarizer(source))

        try {
            val result = reader.decode(bitmap)
            Log.e("BarcodeAnalyzer", "resolved!!! = $result")
        } catch (e: Exception) {
            Log.d("BarcodeAnalyzer", "Error decoding barcode")
        }

    }
}

大功告成，核心代码不超过100行

项目地址：https://github.com/hotstu/QRCodeCameraX

本人在简书上写的内容除特别注明以外均为本人原创，转载需经本人同意，欢迎转载分享，请注明出处。