1. 前言

因为工作中要使用Android Camera2 API，但因为Camera2比较复杂，网上资料也比较乱，有一定入门门槛，所以花了几天时间系统研究了下，并在CSDN上记录了下，希望能帮助到更多的小伙伴。

2. Camera2 API 概述

Camera2 API的包名是android.hardware.camera2，是Android 5.0后推出的一套调用摄像头设备的接口，用来替换原有的Camera。Camera2 API采用管道式的设计，使数据流从摄像头流向Surface，使用Camera2 API实现拍照录制视频功能时，主要涉及到以下几个类：

• CameraManager : Camera设备的管理类，通过该对象可以查询设备的Camera设备信息，得到CameraDevice对象
• CameraDevice:CameraDevice提供了Camera设备相关的一系列固定参数，例如基础的设置和输出格式等。这些信息包含在CameraCharacteristic类中，可以通过getCameraCharacteristics(String)获得该类对象。
• CaptureSession : 在Camera API中，如何需要从Camera设备中获取视频或图片流，首先需要使用输出的Surface和CameraDevice创建一个CameraCaptureSession
• CaptureRequest : 该类中定义了一个Camera设备获取帧数据所需要的参数，可以通过CameraDevice的工厂方法创建一个Request Builder，用于获取CaptureRequest
• CaptureResult : 当处理完一个请求后，会返回一个TotalCaptureResult对象，其中包含Camera设备执行该次Request所使用的参数以及自身状态。

一个Android设备可以有多个摄像头。每个摄像头都是一个摄像头设备，摄像头设备可以同时输出多个流。

3. 前置设置

3.1 添加权限

在AndroidManifest.xml中声明权限

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.CAMERA" />

3.2 申请权限

ActivityCompat.requestPermissions(
        this@MainActivity,
        arrayOf(
            Manifest.permission.CAMERA,
            Manifest.permission.WRITE_EXTERNAL_STORAGE,
            Manifest.permission.RECORD_AUDIO
        ), 123
    )

4. 获取相机列表

4.1 获取摄像头列表

获取摄像头列表需要使用到CameraManager，通过cameraManager.cameraIdList可以获取到摄像头列表

private val cameraManager =
        context.getSystemService(Context.CAMERA_SERVICE) as CameraManager

// 获取所有摄像头的CameraID
fun getCameraIds(): Array<String> {
    return cameraManager.cameraIdList
}

4.2 判断 前/后 摄像头

通过该方法可以获取摄像头的方位，判定是前摄还是后摄

/**
* 获取摄像头方向
*/
fun getCameraOrientationString(cameraId: String): String {
   val characteristics = cameraManager.getCameraCharacteristics(cameraId)
   val lensFacing = characteristics.get(CameraCharacteristics.LENS_FACING)!!
   return when (lensFacing) {
       CameraCharacteristics.LENS_FACING_BACK -> "后摄(Back)"
       CameraCharacteristics.LENS_FACING_FRONT -> "前摄(Front)"
       CameraCharacteristics.LENS_FACING_EXTERNAL -> "外置(External)"
       else -> "Unknown"
   }
}

还有一个简易的判断方式，一般情况下cameraId为0是后摄，cameraId为1是前摄。

4.3 获取一下试试

我们来获取一下试试

val cameraIds = viewModel.getCameraIds()
cameraIds.forEach{ cameraId ->
    val orientation = viewModel.getCameraOrientationString(cameraId)
    Log.i(TAG,"cameraId : $cameraId - $orientation")
}

运行后可以发现打印了日志

cameraId : 0 - 后摄(Back)
cameraId : 1 - 前摄(Front)

5. 实现相机预览

5.1 修改布局

来修改一下XML布局

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/black"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <SurfaceView
        android:id="@+id/surface_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent" />

    <Button
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        android:id="@+id/btn_take_picture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center"
        android:layout_marginBottom="64dp"
        android:text="拍照"/>

</FrameLayout>

5.2 声明相机参数和成员变量

//后摄 : 0 ，前摄 : 1
private val cameraId = "0"
private val TAG = CameraActivity::class.java.simpleName
private lateinit var cameraDevice: CameraDevice
private val cameraThread = HandlerThread("CameraThread").apply { start() }
private val cameraHandler = Handler(cameraThread.looper)
private val cameraManager: CameraManager by lazy {
    getSystemService(Context.CAMERA_SERVICE) as CameraManager
}
private val characteristics: CameraCharacteristics by lazy {
    cameraManager.getCameraCharacteristics(cameraId)
}
private lateinit var session: CameraCaptureSession

5.3 添加SurfaceView回调

添加SurfaceView回调，并在SurfaceView创建的时候，去初始化相机

override fun onCreate(savedInstanceState: Bundle?) {
	super.onCreate(savedInstanceState)
	binding = ActivityCameraBinding.inflate(layoutInflater)
	setContentView(binding.root)
	binding.surfaceView.holder.addCallback(object : SurfaceHolder.Callback {
	    override fun surfaceChanged(holder: SurfaceHolder,format: Int, width: Int,height: Int) = Unit
	
	    override fun surfaceDestroyed(holder: SurfaceHolder) = Unit
	
	    override fun surfaceCreated(holder: SurfaceHolder) {
		    //为了确保设置了大小，需要在主线程中初始化camera
	        binding.root.post {
	             openCamera(cameraId)
	        }
	    }
	})
}

5.4 打开相机

@SuppressLint("MissingPermission")
private fun openCamera(cameraId: String) {
    cameraManager.openCamera(cameraId, object : CameraDevice.StateCallback() {
        override fun onOpened(camera: CameraDevice) {
			cameraDevice = camera
			startPreview()
        }

        override fun onDisconnected(camera: CameraDevice) {
            this@CameraActivity.finish()
        }

        override fun onError(camera: CameraDevice, error: Int) {
            Toast.makeText(application, "openCamera Failed:$error", Toast.LENGTH_SHORT).show()
        }
    }, cameraHandler)
}

5.5 开始预览

private fun startPreview() {
	//因为摄像头设备可以同时输出多个流，所以可以传入多个surface
    val targets = listOf(binding.surfaceView.holder.surface /*,这里可以传入多个surface*/)
    cameraDevice.createCaptureSession(targets, object : CameraCaptureSession.StateCallback() {
        override fun onConfigured(captureSession: CameraCaptureSession) {
        	//赋值session
            session = captureSession

            val captureRequest = cameraDevice.createCaptureRequest(
                CameraDevice.TEMPLATE_PREVIEW
            ).apply { addTarget(binding.surfaceView.holder.surface) }

            //这将不断地实时发送视频流，直到会话断开或调用session.stoprepeat()
            session.setRepeatingRequest(captureRequest.build(), null, cameraHandler)
        }

        override fun onConfigureFailed(session: CameraCaptureSession) {
            Toast.makeText(application,"session configuration failed",Toast.LENGTH_SHORT).show()
        }
    }, cameraHandler)
}

5.6 来看下效果

5.7 修正拉伸形变

5.7.1 新建AutoFitSurfaceView

新建AutoFitSurfaceView继承自SurfaceView，这个类可以调整为我们指定的宽高比，在显示画面的时候进行中心裁剪。

class AutoFitSurfaceView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyle: Int = 0
) : SurfaceView(context, attrs, defStyle) {

    private var aspectRatio = 0f

    /**
     * 设置此视图的宽高比。视图的大小将基于从参数中计算的比率来测量。
     *
     * @param width  相机水平分辨率
     * @param height 相机垂直分辨率
     */
    fun setAspectRatio(width: Int, height: Int) {
        require(width > 0 && height > 0) { "Size cannot be negative" }
        aspectRatio = width.toFloat() / height.toFloat()
        holder.setFixedSize(width, height)
        requestLayout()
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        val width = MeasureSpec.getSize(widthMeasureSpec)
        val height = MeasureSpec.getSize(heightMeasureSpec)
        if (aspectRatio == 0f) {
            setMeasuredDimension(width, height)
        } else {

            // Performs center-crop transformation of the camera frames
            val newWidth: Int
            val newHeight: Int
            val actualRatio = if (width > height) aspectRatio else 1f / aspectRatio
            if (width < height * actualRatio) {
                newHeight = height
                newWidth = (height * actualRatio).roundToInt()
            } else {
                newWidth = width
                newHeight = (width / actualRatio).roundToInt()
            }

            Log.d(TAG, "Measured dimensions set: $newWidth x $newHeight")
            setMeasuredDimension(newWidth, newHeight)
        }
    }

    companion object {
        private val TAG = AutoFitSurfaceView::class.java.simpleName
    }
}

5.7.2 XML布局中将SurfaceView替换为AutoFitSurfaceView

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/black"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <!--<SurfaceView-->
    <com.heiko.mycamera2test.AutoFitSurfaceView
        android:id="@+id/surface_view"
        android:layout_width="match_parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        android:layout_height="match_parent" />

    <Button
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        android:id="@+id/btn_take_picture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center"
        android:layout_marginBottom="64dp"
        android:text="拍照"/>

</FrameLayout>

注意这里根布局不能使用ConstraintLayout，否则宽高比还是会出现问题

5.7.3 获取最大支持的预览大小

新建SmartSize类，这个类通过比较显示的SurfaceView和摄像头支持的分辨率，匹配出最大支持的预览大小

import android.graphics.Point
import android.hardware.camera2.CameraCharacteristics
import android.hardware.camera2.params.StreamConfigurationMap
import android.util.Size
import android.view.Display
import java.lang.Math.max
import java.lang.Math.min

/** Helper class used to pre-compute shortest and longest sides of a [Size] */
class SmartSize(width: Int, height: Int) {
    var size = Size(width, height)
    var long = max(size.width, size.height)
    var short = min(size.width, size.height)
    override fun toString() = "SmartSize(${long}x${short})"
}

/** Standard High Definition size for pictures and video */
val SIZE_1080P: SmartSize = SmartSize(1920, 1080)

/** Returns a [SmartSize] object for the given [Display] */
fun getDisplaySmartSize(display: Display): SmartSize {
    val outPoint = Point()
    display.getRealSize(outPoint)
    return SmartSize(outPoint.x, outPoint.y)
}

/**
 * Returns the largest available PREVIEW size. For more information, see:
 * https://d.android.com/reference/android/hardware/camera2/CameraDevice and
 * https://developer.android.com/reference/android/hardware/camera2/params/StreamConfigurationMap
 */
fun <T>getPreviewOutputSize(
        display: Display,
        characteristics: CameraCharacteristics,
        targetClass: Class<T>,
        format: Int? = null
): Size {

    // Find which is smaller: screen or 1080p
    val screenSize = getDisplaySmartSize(display)
    val hdScreen = screenSize.long >= SIZE_1080P.long || screenSize.short >= SIZE_1080P.short
    val maxSize = if (hdScreen) SIZE_1080P else screenSize

    // If image format is provided, use it to determine supported sizes; else use target class
    val config = characteristics.get(
            CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)!!
    if (format == null)
        assert(StreamConfigurationMap.isOutputSupportedFor(targetClass))
    else
        assert(config.isOutputSupportedFor(format))
    val allSizes = if (format == null)
        config.getOutputSizes(targetClass) else config.getOutputSizes(format)

    // Get available sizes and sort them by area from largest to smallest
    val validSizes = allSizes
            .sortedWith(compareBy { it.height * it.width })
            .map { SmartSize(it.width, it.height) }.reversed()

    // Then, get the largest output size that is smaller or equal than our max size
    return validSizes.first { it.long <= maxSize.long && it.short <= maxSize.short }.size
}

5.7.4 设置宽高比

我们在原本调用openCamera()方法之前的地方，先去设置一下宽高比setAspectRatio()

binding.surfaceView.holder.addCallback(object : SurfaceHolder.Callback {
    //...省略了代码....
    override fun surfaceCreated(holder: SurfaceHolder) {
	    //设置宽高比
	    setAspectRatio()
        //为了确保设置了大小，需要在主线程中初始化camera
        binding.root.post {
            openCamera2(cameraId)
        }
    }
})
	
private fun setAspectRatio() {
	val previewSize = getPreviewOutputSize(
	    binding.surfaceView.display,
	    characteristics,
	    SurfaceHolder::class.java
	)
	Log.d(TAG, "Selected preview size: $previewSize")
	binding.surfaceView.setAspectRatio(previewSize.width, previewSize.height)
}

5.7.5 再次运行预览

可以看到，现在比例显示正常了

5.8 销毁相机

在Activity销毁的时候，我们也要去销毁相机，代码如下

override fun onStop() {
    super.onStop()
    try {
        cameraDevice.close()
    } catch (exc: Throwable) {
        Log.e(TAG, "Error closing camera", exc)
    }
}

override fun onDestroy() {
    super.onDestroy()
    cameraThread.quitSafely()
    //imageReaderThread.quitSafely()
}

6. 其他

6.1 本文源码下载

下载地址 : Android Camera2 Demo - 实现相机预览、拍照、录制视频功能

6.2 Android Camera2 系列

更多Camera2相关文章，请看
十分钟实现 Android Camera2 相机预览_氦客的博客-CSDN博客
十分钟实现 Android Camera2 相机拍照_氦客的博客-CSDN博客
十分钟实现 Android Camera2 视频录制_氦客的博客-CSDN博客

6.3 Android 相机相关文章

Android 使用CameraX实现预览/拍照/录制视频/图片分析/对焦/缩放/切换摄像头等操作_氦客的博客-CSDN博客
Android 从零开发一个简易的相机App_android开发简易app_氦客的博客-CSDN博客

6.4 参考

本文参考文章
[Android进阶] 使用Camera2 API实现一个相机预览页面
实现预览 | Android 开发者 | Android Developers (google.cn)