样例地址：android/camera-samples/Camera2BasicJava/ - Github
大家可以把项目下载到本地并用AndroidStudio打开了再看

简介

在Android5.0的时候，谷歌推出了Camera2API，较上一代Camera1，Camera2支持了很多Camera1所不支持的特性：

更先进的API架构
可以获取更多的帧信息、以及手动控制每一帧的参数
对Camera的控制更加完全
支持更多的格式以及高速连拍
……

API大致的使用流程如下：

通过context.getSystemService(Context.CAMERA_SERVICE)获取CameraManager.
调用CameraManager .open()方法在回调中得到CameraDevice.
通过CameraDevice.createCaptureSession()在回调中获取CameraCaptureSession.
构建CaptureRequest, 有三种模式可选预览/拍照/录像.
通过CameraCaptureSession发送CaptureRequest, capture表示只发一次请求, setRepeatingRequest表示不断发送请求.
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.

CameraActivity

这个类是主要的Activity类，也是唯一的一个Activity。他的代码也很简单：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_camera);
    if (null == savedInstanceState) {
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container, Camera2BasicFragment.newInstance())
                .commit();
    }
}

其实就是调用Camera2BasicFragment的newInstance()方法将Camera2BasicFragment加载进来。

接下来我们看下这个方法

Camera2BasicFragment

Camera2BasicFragment # newInstance()

public static Camera2BasicFragment newInstance() {
    return new Camera2BasicFragment();
}

这就是一个静态方法，返回了一个Camera2BasicFragment的对象。

而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。

Camera2BasicFragment # onCreateView()

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

绑定Layout

Camera2BasicFragment # onViewCreated()

@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);
}

设置点击事件和绑定view

Camera2BasicFragment # onResume()

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

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

那我们来看看startBackgroundThread()方法：

Camera2BasicFragment # startBackgroundThread()

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

这就是开启了一个线程而已。

再来看看openCamera方法

Camera2BasicFragment # openCamera()

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);
    }
}

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

首先判断是否获得Camera权限，如果没有那就去获取。获取权限这块我就不细说，大家可以去了解下Android6.0权限。

接着进入了setUpCameraOutputs方法：

Camera2BasicFragment # setUpCameraOutputs()

private void setUpCameraOutputs(int width, int height) {
Activity activity = getActivity();
CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
try {
    for (String cameraId : manager.getCameraIdList()) {
        CameraCharacteristics characteristics
                = manager.getCameraCharacteristics(cameraId);
    
        // We don't use a front facing camera in this sample.
        // CameraCharacteristics.LENS_FACING 相机设备相对于屏幕的方向
        Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);
        // 如果该摄像头是前置摄像头，就不进行处理
        if (facing != null && facing == CameraCharacteristics.LENS_FACING_FRONT) {
            continue;
        }
    
    
        // 得到该摄像头设备支持的可用流配置；还包括每种格式/尺寸组合的最小帧时长和停顿时长。
        StreamConfigurationMap map = characteristics.get(
                CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        if (map == null) {
            continue;
        }
    
        // For still image captures, we use the largest available size.
        // 对于静态图像捕获，我们使用最大的可用大小。
        Size largest = Collections.max(
                Arrays.asList(map.getOutputSizes(ImageFormat.JPEG)),
                new CompareSizesByArea());
        // ImageReader类允许应用程序直接访问渲染到Surface中的图像数据
        mImageReader = ImageReader.newInstance(largest.getWidth(), largest.getHeight(),
                ImageFormat.JPEG, /*maxImages*/2);
        mImageReader.setOnImageAvailableListener(
                mOnImageAvailableListener, mBackgroundHandler);
    
        // Find out if we need to swap dimension to get the preview size relative to sensor
        // coordinate.
        // 找出是否需要交换尺寸以获得相对于传感器座标的预览尺寸。
        int displayRotation = activity.getWindowManager().getDefaultDisplay().getRotation();
        //noinspection ConstantConditions
        mSensorOrientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);
        boolean swappedDimensions = false;
        switch (displayRotation) {
            case Surface.ROTATION_0:
            case Surface.ROTATION_180:
                if (mSensorOrientation == 90 || mSensorOrientation == 270) {
                    swappedDimensions = true;
                }
                break;
            case Surface.ROTATION_90:
            case Surface.ROTATION_270:
                if (mSensorOrientation == 0 || mSensorOrientation == 180) {
                    swappedDimensions = true;
                }
                break;
            default:
                Log.e(TAG, "Display rotation is invalid: " + displayRotation);
        }
    
        Point displaySize = new Point();
        activity.getWindowManager().getDefaultDisplay().getSize(displaySize);
        int rotatedPreviewWidth = width;
        int rotatedPreviewHeight = height;
        int maxPreviewWidth = displaySize.x;
        int maxPreviewHeight = displaySize.y;
    
        if (swappedDimensions) {
            rotatedPreviewWidth = height;
            rotatedPreviewHeight = width;
            maxPreviewWidth = displaySize.y;
            maxPreviewHeight = displaySize.x;
        }
    
        if (maxPreviewWidth > MAX_PREVIEW_WIDTH) {
            maxPreviewWidth = MAX_PREVIEW_WIDTH;
        }
    
        if (maxPreviewHeight > MAX_PREVIEW_HEIGHT) {
            maxPreviewHeight = MAX_PREVIEW_HEIGHT;
        }
    
        // Danger, W.R.! Attempting to use too large a preview size could exceed the camera
        // bus' bandwidth limitation, resulting in gorgeous previews but the storage of
        // garbage capture data.
    
        // 危险！尝试使用太大的预览大小可能会超出相机总线的带宽限制，导致华丽的预览，但会存储垃圾捕获数据。
        mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class),
                rotatedPreviewWidth, rotatedPreviewHeight, maxPreviewWidth,
                maxPreviewHeight, largest);
    
        // We fit the aspect ratio of TextureView to the size of preview we picked.
        // 我们将TextureView的宽高比与我们选择的预览大小相匹配。
        int orientation = getResources().getConfiguration().orientation;
        if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
            mTextureView.setAspectRatio(
                    mPreviewSize.getWidth(), mPreviewSize.getHeight());
        } else {
            mTextureView.setAspectRatio(
                    mPreviewSize.getHeight(), mPreviewSize.getWidth());
        }
    
        // Check if the flash is supported.
        Boolean available = characteristics.get(CameraCharacteristics.FLASH_INFO_AVAILABLE);
        mFlashSupported = available == null ? false : available;
    
        mCameraId = cameraId;
        return;
    }
} catch (CameraAccessException e) {
    e.printStackTrace();
} catch (NullPointerException e) {
    // Currently an NPE is thrown when the Camera2API is used but not supported on the
    // device this code runs.
    ErrorDialog.newInstance(getString(R.string.camera_error))
            .show(getChildFragmentManager(), FRAGMENT_DIALOG);
    }
}

首先他得到了CameraManager对象。然后就能得到所有摄像头的集合，接着遍历这个集合，先判断是否为前摄像头，如果是的话就跳出，循环下一个摄像头；然后再得到该摄像头支持的流配置，如果没有，就跳出循环下一个；接着在得到该摄像头在JPEG格式下所支持的最大的大小配置，同时配置好ImageReader。

接下来根据摄像头的方向和屏幕方向设置预览的方向以及尺寸。核心方法是chooseOptimalSize()。我们来看下次方法：

Camera2BasicFragment # chooseOptimalSize()

private static Size chooseOptimalSize(Size[] choices, int textureViewWidth,
                                      int textureViewHeight, int maxWidth, int maxHeight, Size aspectRatio) {

    // Collect the supported resolutions that are at least as big as the preview Surface
    List<Size> bigEnough = new ArrayList<>();
    // Collect the supported resolutions that are smaller than the preview Surface
    List<Size> notBigEnough = new ArrayList<>();
    int w = aspectRatio.getWidth();
    int h = aspectRatio.getHeight();
    for (Size option : choices) {
        if (option.getWidth() <= maxWidth && option.getHeight() <= maxHeight &&
                option.getHeight() == option.getWidth() * h / w) {
            if (option.getWidth() >= textureViewWidth &&
                    option.getHeight() >= textureViewHeight) {
                bigEnough.add(option);
            } else {
                notBigEnough.add(option);
            }
        }
    }

    // Pick the smallest of those big enough. If there is no one big enough, pick the
    // largest of those not big enough.
    if (bigEnough.size() > 0) {
        return Collections.min(bigEnough, new CompareSizesByArea());
    } else if (notBigEnough.size() > 0) {
        return Collections.max(notBigEnough, new CompareSizesByArea());
    } else {
        Log.e(TAG, "Couldn't find any suitable preview size");
        return choices[0];
    }
}

首先说一下传进来的参数：

choices：根据预览SurfaceView的得到的摄像头所支持的流配置
textureViewWidth：TextureView的宽
textureViewHeight：TextureView的高
maxWidth：可显示区域的宽
maxHeight：可显示区域的宽
aspectRatio：可使用的最大尺寸

先创建两个集合：bigEnough和notBigEnough。然后再遍历choices，也就是遍历所有SurfaceView所支持的流配置的Size，然后判断宽和高是不是小于maxWidth和maxHeight，以及比例是否相同。然后判端如果尺寸大于TextureView尺寸就放入bigEnough，小于就放入notBigEnough。最后从bigEnough中找到最小的尺寸，如果bigEnough没有就从notBigEnough中找到最大的尺寸。然后返回。

接下来我们回到setUpCameraOutputs()方法
接下来判端了屏幕的方向，是横屏还是竖屏，接着根据即如果配置预览的宽高。最后配置好mFlashSupported和mCameraId变量。方法结束。

Camera2BasicFragment # configureTransform()

然后我们返回openCamera()方法，下面又是configureTransform()方法：

private void configureTransform(int viewWidth, int viewHeight) {
    Activity activity = getActivity();
    if (null == mTextureView || null == mPreviewSize || null == activity) {
        return;
    }
    int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
    Matrix matrix = new Matrix();
    RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
    RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
    float centerX = viewRect.centerX();
    float centerY = viewRect.centerY();
    if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
        bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
        matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
        float scale = Math.max(
                (float) viewHeight / mPreviewSize.getHeight(),
                (float) viewWidth / mPreviewSize.getWidth());
        matrix.postScale(scale, scale, centerX, centerY);
        matrix.postRotate(90 * (rotation - 2), centerX, centerY);
    } else if (Surface.ROTATION_180 == rotation) {
        matrix.postRotate(180, centerX, centerY);
    }
    mTextureView.setTransform(matrix);
}

配置预览图的大小、方向/角度。在此就不多说了。

然后再返回openCamera()方法
下面就是得到CameraManager实例，并通过manager打开Camera，这样相机打开流程就结束了。

Camera2BasicFragment # onPause()

@Override
public void onPause() {
    closeCamera();
    stopBackgroundThread();
    super.onPause();
}
```
具体也不细说了，就是把Camera关闭，并关掉后台线程。

## TextureView.SurfaceTextureListener
我们来看下TextureView的配置。
```java
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) {
    }

};

两个方法都在上面介绍过，也不再细说了。

CameraDevice.StateCallback

我们再来看下这个方法

private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {

    @Override
    public void onOpened(@NonNull CameraDevice cameraDevice) {
        // camera开启时
        mCameraOpenCloseLock.release();
        mCameraDevice = cameraDevice;
        createCameraPreviewSession();
    }

    @Override
    public void onDisconnected(@NonNull CameraDevice cameraDevice) {
        // camera摧毁时
        mCameraOpenCloseLock.release();
        cameraDevice.close();
        mCameraDevice = null;
    }

    @Override
    public void onError(@NonNull CameraDevice cameraDevice, int error) {
        // camera报错时
        mCameraOpenCloseLock.release();
        cameraDevice.close();
        mCameraDevice = null;
        Activity activity = getActivity();
        if (null != activity) {
            activity.finish();
        }
    }

};

首先先来看opOpened方法中的createCameraPreviewSession方法：

Camera2BasicFragment # createCameraPreviewSession()

private void createCameraPreviewSession() {
    try {
        SurfaceTexture texture = mTextureView.getSurfaceTexture();
        assert texture != null;

        // 我们将默认缓冲区的大小配置为所需的相机预览大小。
        texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());

        // 这是我们需要开始预览的输出Surface。
        Surface surface = new Surface(texture);

        // 我们用输出Surface设置CaptureRequest.Builder。
        mPreviewRequestBuilder
                = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
        mPreviewRequestBuilder.addTarget(surface);

        // 在这里，我们为相机预览创建一个CameraCaptureSession
        mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
                new CameraCaptureSession.StateCallback() {

                    @Override
                    public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
                        // 相机已经关闭
                        if (null == mCameraDevice) {
                            return;
                        }

                        // 当会话准备好后，我们开始显示预览。
                        mCaptureSession = cameraCaptureSession;
                        try {
                            // 相机预览时自动对焦应连续。
                            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                                    CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                            // 必要时自动启用flash。
                            setAutoFlash(mPreviewRequestBuilder);

                            // 最后，我们开始显示相机预览。
                            mPreviewRequest = mPreviewRequestBuilder.build();
                            mCaptureSession.setRepeatingRequest(mPreviewRequest,
                                    mCaptureCallback, mBackgroundHandler);
                        } catch (CameraAccessException e) {
                            e.printStackTrace();
                        }
                    }

                    @Override
                    public void onConfigureFailed(
                            @NonNull CameraCaptureSession cameraCaptureSession) {
                        showToast("Failed");
                    }
                }, null
        );
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

然后回到StateCallback。onDisconnected和onError的内容相似，区别就是onError退出的同时把Activity也强制关闭了。

CameraCaptureSession.CaptureCallback

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

    private void process(CaptureResult result) {
        switch (mState) {
            case STATE_PREVIEW: {
                // 当相机预览正常工作时，我们什么也不做。
                break;
            }
            case STATE_WAITING_LOCK: {
                Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
                if (afState == null) {
                    captureStillPicture();
                } else if (CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED == afState ||
                        CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED == afState) {
                    // CONTROL_AE_STATE在某些设备上可以为空
                    Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
                    if (aeState == null ||
                            aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED) {
                        mState = STATE_PICTURE_TAKEN;
                        captureStillPicture();
                    } else {
                        runPrecaptureSequence();
                    }
                }
                break;
            }
            case STATE_WAITING_PRECAPTURE: {
                // CONTROL_AE_STATE在某些设备上可以为空
                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_WAITING_NON_PRECAPTURE;
                }
                break;
            }
            case STATE_WAITING_NON_PRECAPTURE: {
                // CONTROL_AE_STATE在某些设备上可以为空
                Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
                if (aeState == null || aeState != CaptureResult.CONTROL_AE_STATE_PRECAPTURE) {
                    mState = STATE_PICTURE_TAKEN;
                    captureStillPicture();
                }
                break;
            }
        }
    }

这块也没啥多讲的，看下注释。

然后再看看captureStillPicture()方法:

Camera2BasicFragment # captureStillPicture()

private void captureStillPicture() {
    try {
        final Activity activity = getActivity();
        if (null == activity || null == mCameraDevice) {
            return;
        }
        // 这是我们用来拍照的capturerequest.builder。
        final CaptureRequest.Builder captureBuilder =
                mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
        captureBuilder.addTarget(mImageReader.getSurface());

        // 使用与预览相同的ae和af模式。
        captureBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
        setAutoFlash(captureBuilder);

        // Orientation
        int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
        captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));

        CameraCaptureSession.CaptureCallback captureCallback
                = new CameraCaptureSession.CaptureCallback() {

            @Override
            public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                                           @NonNull CaptureRequest request,
                                           @NonNull TotalCaptureResult result) {
                showToast("Saved: " + mFile);
                Log.d(TAG, mFile.toString());
                unlockFocus();
            }
        };

        mCaptureSession.stopRepeating();
        mCaptureSession.abortCaptures();
        mCaptureSession.capture(captureBuilder.build(), captureCallback, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

看到这里代码已经不复杂了，组装好我们的请求然后用CameraCaptureSession发送这个请求就可以了。

Camera2官方样例解读

简介

CameraActivity

Camera2BasicFragment

Camera2BasicFragment # newInstance()

Camera2BasicFragment # onCreateView()

Camera2BasicFragment # onViewCreated()

Camera2BasicFragment # onResume()

Camera2BasicFragment # startBackgroundThread()

Camera2BasicFragment # openCamera()

Camera2BasicFragment # setUpCameraOutputs()

Camera2BasicFragment # chooseOptimalSize()

Camera2BasicFragment # configureTransform()

Camera2BasicFragment # onPause()

CameraDevice.StateCallback

Camera2BasicFragment # createCameraPreviewSession()

CameraCaptureSession.CaptureCallback

Camera2BasicFragment # captureStillPicture()

.Net 8.0 下的新RPC，IceRPC之试试的新玩法"打洞"

关于游戏付费的一点想法

我通过CKA和CKS啦！

《最新出炉》系列入门篇-Python+Playwright自动化测试-42-强大的可视化追踪利器Trace Viewer

大数据怎么学？对大数据开发领域及岗位的详细解读，完整理解大数据开发领域技术体系

Android源碼之SharedPreferences

LiveData的map()和switchMap

Kotlin入門(四)——類和對象的進階

Flutter入門並實戰天氣預報APP(1)——Flutter安裝

操作系統6--死鎖

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

linux以太網驅動總結