Camera2 API简介

Android 从5.0（21）开始，引入了新的Camera API Camera2，原来的android.hardware.Camera被废弃(下面称为Camera1)，还有一个android.graphics.Camera，这个android.graphics.Camera不是用来照相的，是用来处理图像的，可以做出3D的图像效果之类的，之前的Camera1则由android.hardware.Camera代替。Camera2支持RAW输出，可以调节曝光，对焦模式，快门等，功能比原先Camera强大。

这里引用了管道的概念将安卓设备和摄像头之间联通起来，系统向摄像头发送 Capture 请求，而摄像头会返回 CameraMetadata。这一切建立在一个叫作 CameraCaptureSession 的会话中。

• CameraManaer 摄像头管理器，用于检测摄像头，打开系统摄像头，调用CameraManager.getCameraCharacteristics(String)可以获取指定摄像头的相关特性

• CameraCharacteristics 摄像头的特性

• CameraDevice 摄像头，类似android.hardware.Camera也就是Camera1的Camera

• CameraCaptureSession 这个类控制摄像头的预览或者拍照，setRepeatingRequest()开启预览，capture()拍照，CameraCaptureSession提供了StateCallback、CaptureCallback两个接口来监听CameraCaptureSession的创建和拍照过程。

• CameraRequest和CameraRequest.Builder，预览或者拍照时，都需要一个CameraRequest对象。CameraRequest表示一次捕获请求，用来对照片的各种参数设置，比如对焦模式、曝光模式等。CameraRequest.Builder用来生成CameraRequest对象。

Camera2的简单使用（使用SurfaceView）

主要步骤：

1. 获得摄像头管理器CameraManager mCameraManager，mCameraManager.openCamera()来打开摄像头
2. 指定要打开的摄像头，并创建openCamera()所需要的CameraDevice.StateCallback stateCallback
3. 在CameraDevice.StateCallback stateCallback中调用takePreview()，这个方法中，使用CaptureRequest.Builder创建预览需要的CameraRequest，并初始化了CameraCaptureSession，最后调用了setRepeatingRequest(previewRequest, null, childHandler)进行了预览
4. 点击拍照按钮，调用takePicture()，这个方法内，最终调用了capture(mCaptureRequest, null, childHandler)
5. 在new ImageReader.OnImageAvailableListener(){}回调方法中，将拍照拿到的图片进行展示

package org.hunter.a361camera.view;

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.ImageFormat;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CaptureRequest;
import android.media.Image;
import android.media.ImageReader;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.support.annotation.Nullable;
import android.support.annotation.RequiresApi;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.Fragment;
import android.util.SparseIntArray;
import android.view.LayoutInflater;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.Toast;

import org.hunter.a361camera.R;

import java.nio.ByteBuffer;
import java.util.Arrays;

import static android.os.Looper.getMainLooper;

/**
 * Main UI for the statistics screen.
 */
public class CameraFragment extends Fragment {
    public static final int REQUEST_CAMERA_CODE = 100;
    public static final String PACKAGE = "package:";

    private static final SparseIntArray ORIENTATIONS = new SparseIntArray();

    ///为了使照片竖直显示
    static {
        ORIENTATIONS.append(Surface.ROTATION_0, 90);
        ORIENTATIONS.append(Surface.ROTATION_90, 0);
        ORIENTATIONS.append(Surface.ROTATION_180, 270);
        ORIENTATIONS.append(Surface.ROTATION_270, 180);
    }

    private SurfaceView mSurfaceView;
    private SurfaceHolder mSurfaceHolder;
    private ImageView iv_show;
    private ImageView mCatture;
    private CameraManager mCameraManager;//摄像头管理器
    private Handler childHandler, mainHandler;
    private String mCameraID;//摄像头Id 0 为后  1 为前
    private ImageReader mImageReader;
    private CameraCaptureSession mCameraCaptureSession;
    private CameraDevice mCameraDevice;
    /**
     * 摄像头创建监听
     */
    private CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice camera) {//打开摄像头
            mCameraDevice = camera;
            //开启预览
            takePreview();
        }

        @Override
        public void onDisconnected(CameraDevice camera) {//关闭摄像头
            if (null != mCameraDevice) {
                mCameraDevice.close();
                CameraFragment.this.mCameraDevice = null;
            }
        }

        @Override
        public void onError(CameraDevice camera, int error) {//发生错误
            Toast.makeText(getContext(), "摄像头开启失败", Toast.LENGTH_SHORT).show();
        }
    };

    public static CameraFragment newInstance() {
        return new CameraFragment();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.camera_frag, container, false);
        initVIew(root);
        initListener();
        return root;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    /**
     * 初始化
     */
    private void initVIew(View root) {
        iv_show = (ImageView) root.findViewById(R.id.iv_show_camera2);
        //mSurfaceView
        mSurfaceView = (SurfaceView) root.findViewById(R.id.surface_view_camera2);
        mCatture = (ImageView) root.findViewById(R.id.capture);
        mSurfaceHolder = mSurfaceView.getHolder();
        mSurfaceHolder.setKeepScreenOn(true);
        // mSurfaceView添加回调
        mSurfaceHolder.addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) { //SurfaceView创建
                // 初始化Camera
                initCamera2();
            }

            @Override
            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) { //SurfaceView销毁
                // 释放Camera资源
                if (null != mCameraDevice) {
                    mCameraDevice.close();
                    CameraFragment.this.mCameraDevice = null;
                }
            }
        });
    }

    /**
     * 初始化Camera2
     */
    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    private void initCamera2() {
        HandlerThread handlerThread = new HandlerThread("Camera2");
        handlerThread.start();
        childHandler = new Handler(handlerThread.getLooper());
        mainHandler = new Handler(getMainLooper());
        mCameraID = "" + CameraCharacteristics.LENS_FACING_FRONT;//后摄像头
        mImageReader = ImageReader.newInstance(1080, 1920, ImageFormat.JPEG, 1);
        mImageReader.setOnImageAvailableListener(new ImageReader.OnImageAvailableListener() { //可以在这里处理拍照得到的临时照片 例如，写入本地
            @Override
            public void onImageAvailable(ImageReader reader) {
                //mCameraDevice.close();
                // 拿到拍照照片数据
                Image image = reader.acquireNextImage();
                ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                byte[] bytes = new byte[buffer.remaining()];
                buffer.get(bytes);//由缓冲区存入字节数组
                final Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
                if (bitmap != null) {
                    iv_show.setImageBitmap(bitmap);
                }
            }
        }, mainHandler);
        //获取摄像头管理
        mCameraManager = (CameraManager) getContext().getSystemService(Context.CAMERA_SERVICE);
        try {
            if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                //申请WRITE_EXTERNAL_STORAGE权限
                requestPermissions(new String[]{Manifest.permission.CAMERA},
                        REQUEST_CAMERA_CODE);
                //return;
            } else {
                //打开摄像头
                mCameraManager.openCamera(mCameraID, stateCallback, mainHandler);
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == REQUEST_CAMERA_CODE) {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                // Permission Granted
                try {
                    mCameraManager.openCamera(mCameraID, stateCallback, mainHandler);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                } catch (SecurityException e) {
                    e.printStackTrace();
                }
            } else {
                // Permission Denied
            }
        }
    }

    /**
     * 开始预览
     */
    private void takePreview() {
        try {
            // 创建预览需要的CaptureRequest.Builder
            final CaptureRequest.Builder previewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            // 将SurfaceView的surface作为CaptureRequest.Builder的目标
            previewRequestBuilder.addTarget(mSurfaceHolder.getSurface());
            // 创建CameraCaptureSession，该对象负责管理处理预览请求和拍照请求
            mCameraDevice.createCaptureSession(Arrays.asList(mSurfaceHolder.getSurface(), mImageReader.getSurface()), new CameraCaptureSession.StateCallback() // ③
            {
                @Override
                public void onConfigured(CameraCaptureSession cameraCaptureSession) {
                    if (null == mCameraDevice) return;
                    // 当摄像头已经准备好时，开始显示预览
                    mCameraCaptureSession = cameraCaptureSession;
                    try {
                        // 自动对焦
                        previewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                        // 打开闪光灯
                        previewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
                        // 显示预览
                        CaptureRequest previewRequest = previewRequestBuilder.build();
                        mCameraCaptureSession.setRepeatingRequest(previewRequest, null, childHandler);
                    } catch (CameraAccessException e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onConfigureFailed(CameraCaptureSession cameraCaptureSession) {
                    Toast.makeText(getContext(), "配置失败", Toast.LENGTH_SHORT).show();
                }
            }, childHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    /**
     * 拍照
     */
    private void takePicture() {
        if (mCameraDevice == null) return;
        // 创建拍照需要的CaptureRequest.Builder
        final CaptureRequest.Builder captureRequestBuilder;
        try {
            captureRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            // 将imageReader的surface作为CaptureRequest.Builder的目标
            captureRequestBuilder.addTarget(mImageReader.getSurface());
            // 自动对焦
            captureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            // 自动曝光
            captureRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
            // 获取手机方向
            int rotation = getActivity().getWindowManager().getDefaultDisplay().getRotation();
            // 根据设备方向计算设置照片的方向
            captureRequestBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));
            //拍照
            CaptureRequest mCaptureRequest = captureRequestBuilder.build();
            mCameraCaptureSession.capture(mCaptureRequest, null, childHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void initListener() {
        mCatture.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                takePicture();
            }
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

    <SurfaceView
        android:id="@+id/surface_view_camera2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <org.hunter.a361camera.widget.PorterDuffViewImageView
        android:id="@+id/capture"
        android:layout_width="90dp"
        android:layout_height="90dp"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="20dp"
        android:src="@mipmap/capture"/>

    <org.hunter.a361camera.widget.PorterDuffViewImageView
        android:id="@+id/iv_show_camera2"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_marginBottom="20dp"
        android:layout_marginRight="20dp"
        android:scaleType="centerCrop"/>
</RelativeLayout>