camera2 Google官方demo android-Camera2Basic解读

样例地址：官方demo

1. 通过context.getSystemService(Context.CAMERA_SERVICE)获取CameraManager.
2. 调用CameraManager .open()方法在回调中得到CameraDevice.
3. 通过CameraDevice.createCaptureSession()在回调中获取CameraCaptureSession.
4. 构建CaptureRequest, 有三种模式可选 预览/拍照/录像.
5. 通过CameraCaptureSession发送CaptureRequest, capture表示只发一次请求, setRepeatingRequest表示不断发送请求.
6. 拍照数据可以在ImageReader.OnImageAvailableListener回调中获取, CaptureCallback中则可获取拍照实际的参数和Camera当前状态.

demoJava代码：
AutoFitTextureView提供了一个方法用来设置textureView的宽高，
Camera2BasicFragment拍照流程（主要分析）
CameraActivityz中调用Camera2BasicFragment的newInstance()方法加入了一个fragment，

Camera2BasicFragment
Camera2BasicFragment是什么，他是一个Fragment，所以我们就从一个Fragment的生命周期开始看起。
onCreateView() 绑定Layout

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
   
    return inflater.inflate(R.layout.fragment_camera2_basic, container, false);
}

onViewCreated() 设置点击事件和绑定view

@Override
public void onViewCreated(final View view, Bundle savedInstanceState) {
   
    view.findViewById(R.id.picture).setOnClickListener(this);
    view.findViewById(R.id.info).setOnClickListener(this);
    mTextureView = view.findViewById(R.id.texture);
}

onResume() 开启相机操作
1.进入相机，获取TextureView对象，然后开启一个后台线程处理相机数据
2.判断TextureView是否有效，有效就直接openCamera()，无效就加入一个监听SufaceTextureListener，通过回调确保surfaceTexture有效，然后同样openCamera()。

@Override
public void onResume() {
   
    super.onResume();
    startBackgroundThread(); //开启一个后台线程处理相机数据

    if (mTextureView.isAvailable()) {
   
        openCamera(mTextureView.getWidth(), mTextureView.getHeight());
    } else {
   
        mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
    }
}

TextureView.SurfaceTextureListener
我们来看下TextureView的配置。

private final TextureView.SurfaceTextureListener mSurfaceTextureListener
        = new TextureView.SurfaceTextureListener() {
   

    // 在view或view的祖先的可见性更改时调用。
    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture texture, int width, int height) {
   
        openCamera(width, height);
    }

    // 当此view的大小更改时调用此方法。
    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture texture, int width, int height) {
   
        configureTransform(width, height);
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture texture) {
   
        return true;
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture texture) {
   
    }

};

startBackgroundThread()

private void startBackgroundThread() {
   
    mBackgroundThread = new HandlerThread("CameraBackground");
    mBackgroundThread.start();
    mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}

openCamera() 此处将mTextureView的宽和高传进来了。其中mTextureView就是预览的窗口View。

private void openCamera(int width, int height) {
   
    // 获取权限
    if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.CAMERA)
            != PackageManager.PERMISSION_GRANTED) {
   
        requestCameraPermission();
        return;
    }
    setUpCameraOutputs(width, height);
    configureTransform(width, height);
    Activity activity = getActivity();
    CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
    try {
   
        if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
   
            throw new RuntimeException("Time out waiting to lock camera opening.");
        }
        manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
    } catch (CameraAccessException e) {
   
        e.printStackTrace();
    } catch (InterruptedException e) {
   
        throw new RuntimeException("Interrupted while trying to lock camera opening.", e);
    }
}

3.设置相机特性–setUpCameraOutputs()，设置图片存储监听OnImageAvaliableListener，拍照图片有效会通知ImageSaver线程保存图片，设置AE，AF等
setUpCameraOutputs()

private void setUpCameraOutputs(int width, int height) {