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：

源码：