android.hardware.camera2使用指南

android.hardware.camera2使用指南

API 21中将原来的camera API弃用转而推荐使用新增的camera2 API，这是一个大的动作，因为新API换了架构，让开发者用起来更难了。

先来看看camera2包架构示意图：



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。

下面是camera2包中的主要类：



其中CameraManager是那个站在高处统管所有摄像投设备（CameraDevice）的管理者，而每个CameraDevice自己会负责建立CameraCaptureSession以及建立CaptureRequest。CameraCharacteristics是CameraDevice的属性描述类，非要做个对比的话，那么它与原来的CameraInfo有相似性。

类图中有着三个重要的callback，虽然这增加了阅读代码的难度，但是你必须要习惯，因为这是新包的风格。其中CameraCaptureSession.CaptureCallback将处理预览和拍照图片的工作，需要重点对待。

这些类是如何相互配合的？下面是简单的流程图。



我是用SurfaceView作为显示对象（当然还可以TextureView去显示，详见参考中的项目）

核心代码如下：

mCameraManager = (CameraManager) this.getSystemService(Context.CAMERA_SERVICE);
mSurfaceView = (SurfaceView)findViewById(R.id.surfaceview);
mSurfaceHolder = mSurfaceView.getHolder();
mSurfaceHolder.addCallback(new SurfaceHolder.Callback() {
@Override
public void surfaceCreated(SurfaceHolder holder) {
initCameraAndPreview();
}
});

private void initCameraAndPreview() {
Log.d(linc,init camera and preview);
HandlerThread handlerThread = new HandlerThread(Camera2);
handlerThread.start();
mHandler = new Handler(handlerThread.getLooper());
try {
mCameraId = +CameraCharacteristics.LENS_FACING_FRONT;
mImageReader = ImageReader.newInstance(mSurfaceView.getWidth(), mSurfaceView.getHeight(),
ImageFormat.JPEG,/*maxImages*/7);
mImageReader.setOnImageAvailableListener(mOnImageAvailableListener, mHandler);

mCameraManager.openCamera(mCameraId, DeviceStateCallback, mHandler);
} catch (CameraAccessException e) {
Log.e(linc, open camera failed. + e.getMessage());
}
}

private CameraDevice.StateCallback DeviceStateCallback = new CameraDevice.StateCallback() {

@Override
public void onOpened(CameraDevice camera) {
Log.d(linc,DeviceStateCallback:camera was opend.);
mCameraOpenCloseLock.release();
mCameraDevice = camera;
try {
createCameraCaptureSession();
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
};

private void createCameraCaptureSession() throws CameraAccessException {
Log.d(linc,createCameraCaptureSession);

mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
mPreviewBuilder.addTarget(mSurfaceHolder.getSurface());
mState = STATE_PREVIEW;
mCameraDevice.createCaptureSession(
Arrays.asList(mSurfaceHolder.getSurface(), mImageReader.getSurface()),
mSessionPreviewStateCallback, mHandler);
}

private CameraCaptureSession.StateCallback mSessionPreviewStateCallback = new
CameraCaptureSession.StateCallback() {

@Override
public void onConfigured(CameraCaptureSession session) {
Log.d(linc,mSessionPreviewStateCallback onConfigured);
mSession = session;
try {
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, mHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
Log.e(linc,set preview builder failed.+e.getMessage());
}
}
};

private CameraCaptureSession.CaptureCallback mSessionCaptureCallback =
new CameraCaptureSession.CaptureCallback() {

@Override
public void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request,
TotalCaptureResult result) {
//            Log.d(linc,mSessionCaptureCallback, onCaptureCompleted);
mSession = session;
checkState(result);
}

@Override
public void onCaptureProgressed(CameraCaptureSession session, CaptureRequest request,
CaptureResult partialResult) {
Log.d(linc,mSessionCaptureCallback, onCaptureProgressed);
mSession = session;
checkState(partialResult);
}

private void checkState(CaptureResult result) {
switch (mState) {
case STATE_PREVIEW:
// NOTHING
break;
case STATE_WAITING_CAPTURE:
int afState = result.get(CaptureResult.CONTROL_AF_STATE);

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) {
//do something like save picture
}
break;
}
}

};

按下capture按钮：

public void onCapture(View view) {
try {
Log.i(linc, take picture);
mState = STATE_WAITING_CAPTURE;
mSession.setRepeatingRequest(mPreviewBuilder.build(), mSessionCaptureCallback, mHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}

测试用genemotion模拟器，直接调用笔记本的摄像头。

配置图如下：



demo界面如下图：