Camera2 打开相机预览界面

camera2 是21之后的api用于代替Camera，提供更加牛X的对相机hardware操作的api

参考资料:http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2015/0428/2811.html
http://www.tuicool.com/articles/6b67Nra

此篇笔记主要是记录打开预览界面
后面会记录Camera打开相机预览的代码，对比一下

界面布局

<?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"><com.arvin.camera3.view.AutoFitTextureView
        android:id="@+id/surface"android:layout_width="wrap_content"android:layout_height="wrap_content" /><Button
        android:id="@+id/capturebtn"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentBottom="true"android:layout_centerHorizontal="true"android:text="拍照" /><ImageView
        android:id="@+id/preview"android:layout_width="120dp"android:layout_height="120dp"android:layout_alignParentBottom="true" /></RelativeLayout>

AutoFitTextureView 继承自 TextureVeiw

1.首先要初始化view，就是一些findviewbyid

2.示例代码是在onResume中，能否有更好方式？？？？

if (surfaceView.isAvailable()) {// FIXME: 2016/6/13try {openCamera(surfaceView.getWidth(), surfaceView.getHeight());} catch (Exception e) {e.printStackTrace();}
} else {surfaceView.setSurfaceTextureListener(mSurfaceTextureListener);
}

surfaceView即TextureView

判断TextureView状态
可用，打开相机，否则设置相应的回调

先看打开相机的代码

private void openCamera(int width, int height) throws Exception {Activity activity = getActivity();CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);if (mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {manager.openCamera(mCameraId,deviceStateCallback,mPreviewHandler );}
}

首先调用getSystemService(Context.CAMERA_SERVICE),拿到CameraManager实例，
注：Api 21 新增的，无兼容包，估计也不会发布兼容包吧，21之后 Camera已弃用
然后通过CameraManager实例的 openCamera()方法打开相机预览
我们看下openCamera的声明

@RequiresPermission(android.Manifest.permission.CAMERA)
public void openCamera(@NonNull String cameraId,@NonNull final CameraDevice.StateCallback callback, @Nullable Handler handler)throws CameraAccessException {if (cameraId == null) {throw new IllegalArgumentException("cameraId was null");} else if (callback == null) {throw new IllegalArgumentException("callback was null");} else if (handler == null) {if (Looper.myLooper() != null) {handler = new Handler();} else {throw new IllegalArgumentException("Handler argument is null, but no looper exists in the calling thread");}}openCameraDeviceUserAsync(cameraId, callback, handler);
}

@RequiresPermission(android.Manifest.permission.CAMERA)

需要camera权限，在camera声明，android 6.0之后需要请求，属于runtime permission

需要传入三个参数
cameraId ： “0”表示后置摄像头，“1”表示前置摄像头
callback : CameraDevice.StateCallback 相机状态回调
注：CameraDevice 实例代表一个相机
handler : hanlder

回头看如果TextureView不可用的状态下

surfaceView.setSurfaceTextureListener(mSurfaceTextureListener);

看下 mSurfaceTextureListener是个什么东西

private final TextureView.SurfaceTextureListener mSurfaceTextureListener = new TextureView.SurfaceTextureListener() {@Overridepublic void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {try {openCamera(width, height);} catch (Exception e) {e.printStackTrace();}}@Overridepublic void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {}@Overridepublic boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {return false;}@Overridepublic void onSurfaceTextureUpdated(SurfaceTexture surface) {}
};

这个有点和SurfaceView的回调相似了
设置回调，然后当surface可用的时候openCamera(),回到上面的流程去了
包含四个方法，分别对应可用，尺寸发生变化，TextureView销毁，以及更新的时候回调

继续看manager.openCamera();
已经说了第一个参数camreaId，“0”代表后置摄像头，“1”代表前置摄像头
第二个参数CameraDevice.StateCallback，直接看

CameraDevice.StateCallback deviceStateCallback = new CameraDevice.StateCallback() {@Overridepublic void onOpened(CameraDevice camera) {mCameraOpenCloseLock.release();mCameraDevice = camera;try {createCameraPreviewSession();} catch (CameraAccessException e) {e.printStackTrace();}}@Overridepublic void onDisconnected(CameraDevice camera) {mCameraOpenCloseLock.release();camera.close();mCameraDevice = null;}@Overridepublic void onError(CameraDevice camera, int error) {mCameraOpenCloseLock.release();camera.close();mCameraDevice = null;Toast.makeText(getActivity(), "onError,error--->" + error, Toast.LENGTH_SHORT).show();}
};

通过代码可知，CameraDevice.StateCallback 提供了三个回调方法，分别对应于camrea打开，失去连接，打开错误的时候回调，
在打开的时候会调用createCameraPreviewSession() ，看一下方法定义

private void createCameraPreviewSession() throws CameraAccessException {initSurface();mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);mPreviewBuilder.addTarget(mSurface);mCameraDevice.createCaptureSession(Arrays.asList(mSurface), mCaptureSessionStateCallback, mPreviewHandler);
}private void initSurface() {SurfaceTexture sufaceTexture = surfaceView.getSurfaceTexture();assert sufaceTexture != null;sufaceTexture.setDefaultBufferSize(surfaceView.getWidth(), surfaceView.getHeight());mSurface = new Surface(sufaceTexture);
}

首先通过TextureView的getSurfaceTexture() 拿到对应 SurfaceTexture 是不是SurfaceView的getSurfaceHolder()很像
设置显示大小，创建Surface实例
之后，调用 CameraDevice createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW) 创建预览请求
并设置target, CaptureRequest.Builder addTarget(Surface surface)
然后调用CameraDevice createCaptureSession()，创建一个相机回话

createCaptureSession()需要传入三个参数
看下声明

public abstract void createCaptureSession(@NonNull List<Surface> outputs,@NonNull CameraCaptureSession.StateCallback callback, @Nullable Handler handler)

List outputs 我的理解是预览的输出载体列表，在上面的代码中，我们传入了new Surface(TextureView.getSurface()) 对象
ImageReader 也有 getSurface()方法，ImageReader也可以作为输出载体

第二个参数CameraCaptureSession.StateCallback 摄像头采集状态回调
直接看代码

private CameraCaptureSession.StateCallback mCaptureSessionStateCallback = new CameraCaptureSession.StateCallback() {@Overridepublic void onConfigured(CameraCaptureSession session) {if (null == mCameraDevice) {return;}mSession = session;mPreviewBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);mPreviewBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);try {session.setRepeatingRequest(mPreviewBuilder.build(), mSessionCaptureCallback, mPreviewHandler);} catch (CameraAccessException e) {e.printStackTrace();}}@Overridepublic void onConfigureFailed(CameraCaptureSession session) {}};

设置拍摄模式，这里设置了连拍，flash，其他的模式嘛，我也不清楚了

mPreviewBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
mPreviewBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);session.setRepeatingRequest(mPreviewBuilder.build(), mSessionCaptureCallback, mPreviewHandler);

设置重复请求，字面上这么理解

同样是三个参数
第一个是CaptureRequest.Builder buildI() 这个是前面采集请求builder 通过CameraDevice createCaptureRequest创建的
第二个是摄像头采集回话采集状态的回调

private CameraCaptureSession.CaptureCallback mSessionCaptureCallback = new CameraCaptureSession.CaptureCallback() {@Overridepublic void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request, TotalCaptureResult result) {super.onCaptureCompleted(session, request, result);}@Overridepublic void onCaptureProgressed(CameraCaptureSession session, CaptureRequest request, CaptureResult partialResult) {super.onCaptureProgressed(session, request, partialResult);}
};

包含两个状态，采集进行，采集完成
可以在这里面去做处理，
贴上一段代码

private CameraCaptureSession.CaptureCallback mSessionCaptureCallback = new CameraCaptureSession.CaptureCallback() {@Overridepublic void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request, TotalCaptureResult result) {mSession = session;if (!PreferenceHelper.getCameraFormat(getActivity()).equals("DNG")) {checkState(result);}}@Overridepublic void onCaptureProgressed(CameraCaptureSession session, CaptureRequest request, CaptureResult partialResult) {mSession = session;if (!PreferenceHelper.getCameraFormat(getActivity()).equals("DNG")) {checkState(partialResult);}}private void checkState(CaptureResult result) {
//            mFrameBitmap = mPreviewView.getBitmap();
//            mMainHandler.sendEmptyMessage(1);switch (mState) {case STATE_PREVIEW:// NOTHINGbreak;case STATE_WAITING_CAPTURE:int afState = result.get(CaptureResult.CONTROL_AF_STATE);Log.i("checkState", "afState--->" + afState);if (CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED == afState || CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED == afState|| CaptureResult.CONTROL_AF_STATE_PASSIVE_FOCUSED == afState || CaptureResult.CONTROL_AF_STATE_PASSIVE_UNFOCUSED == afState) {Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);Log.i("checkState", "进来了一层,aeState--->" + aeState);if (aeState == null || aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED) {Log.i("checkState", "进来了第二层");mState = STATE_TRY_DO_CAPTURE;doStillCapture();} else {mState = STATE_TRY_CAPTURE_AGAIN;tryCaptureAgain();}}break;case STATE_TRY_CAPTURE_AGAIN:Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);if (aeState == null ||aeState == CaptureResult.CONTROL_AE_STATE_PRECAPTURE ||aeState == CaptureRequest.CONTROL_AE_STATE_FLASH_REQUIRED) {mState = STATE_TRY_DO_CAPTURE;}break;case STATE_TRY_DO_CAPTURE:aeState = result.get(CaptureResult.CONTROL_AE_STATE);if (aeState == null || aeState != CaptureResult.CONTROL_AE_STATE_PRECAPTURE) {mState = STATE_TRY_DO_CAPTURE;doStillCapture();}break;}}
};

至此,打开相机预览的代码就结束了，后续比如拍照，录像什么的以后再分析啦，这里的api还没在学习中

最后附上Camera打开预览的代码，感觉要简单好多呀

//布局文件
<SurfaceViewandroid:id="@+id/surface"android:layout_width="match_parent"android:layout_height="match_parent" />Camera camera;
surfaceView = (SurfaceView) findViewById(R.id.surface);
holder = surfaceView.getHolder();
holder.addCallback(this);  //设置回调@Override
public void surfaceCreated(SurfaceHolder holder) {camera = Camera.open();try {camera.setPreviewDisplay(holder);} catch (IOException e) {e.printStackTrace();}camera.startPreview();
}//将camera预览界面绑定到SurfaceView
//startPreview()@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}@Override
public void surfaceDestroyed(SurfaceHolder holder) {}

代码是不是比camera2简单多了，不过这个预览界面挺难看的，其他设置也没有仔细研究，用到的时候再说吧

文中参考了
Android实战技巧之三十三：android.hardware.camera2使用指南
再此对原作者表示感谢

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