Android调用Camera API 拍照

注意，Camera API在API>=21已经被废弃了，建议使用android.hardware.camera2 API来进行操作。

调用Camera API拍照的流程如下：

To take pictures with this class, use the following steps:

Obtain an instance of Camera from open(int).
Get existing (default) settings with getParameters().
If necessary, modify the returned Camera.Parameters object and call setParameters(Camera.Parameters).
If desired, call setDisplayOrientation(int).
Important: Pass a fully initialized SurfaceHolder to setPreviewDisplay(SurfaceHolder). Without a surface, the camera will be unable to start the preview.
Important: Call startPreview() to start updating the preview surface. Preview must be started before you can take a picture.
When you want, call takePicture(Camera.ShutterCallback, Camera.PictureCallback, Camera.PictureCallback, Camera.PictureCallback) to capture a photo. Wait for the callbacks to provide the actual image data.
After taking a picture, preview display will have stopped. To take more photos, call startPreview() again first.
Call stopPreview() to stop updating the preview surface.
Important: Call release() to release the camera for use by other applications. Applications should release the camera immediately in onPause() (and re-open() it in onResume()).

1、声明所需权限

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />

2、通过Camera.open()获取Camera实例，对于多个摄像头，那么需要遍历getNumberOfCameras()，获取每一个CameraInfo来判断是前置摄像头还是后置摄像头。

int cameraId = 0 ;
int numberOfCameras = Camera.getNumberOfCameras();
CameraInfo cameraInfo = new CameraInfo();
for (int i = 0; i < numberOfCameras; i++) {
　　Camera.getCameraInfo(i, cameraInfo);
　　if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
　　　　cameraId  = i ;
　　　　break ;
 　　}
 }

3、Camera.Parameters类是对Camera的设置操作，包括闪光灯、自动对焦，场景，白平衡等，有需要可以设置。

PS：闪光灯就是setFlashMode(Camera.Parameters.FLASH_MODE_TORCH)来实现的

4、设置Camera的方向，官方提供的算法如下：

public static void setCameraDisplayOrientation(Activity activity,
         int cameraId, android.hardware.Camera camera) {
     android.hardware.Camera.CameraInfo info =
             new android.hardware.Camera.CameraInfo();
     android.hardware.Camera.getCameraInfo(cameraId, info);
     int rotation = activity.getWindowManager().getDefaultDisplay()
             .getRotation();
     int degrees = 0;
     switch (rotation) {
         case Surface.ROTATION_0: degrees = 0; break;
         case Surface.ROTATION_90: degrees = 90; break;
         case Surface.ROTATION_180: degrees = 180; break;
         case Surface.ROTATION_270: degrees = 270; break;
     }

     int result;
     if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
         result = (info.orientation + degrees) % 360;
         result = (360 - result) % 360;  // compensate the mirror
     } else {  // back-facing
         result = (info.orientation - degrees + 360) % 360;
     }
     camera.setDisplayOrientation(result);
 }

5、设置预览视图（SurfaceHolder），一般在xml里面自定义SurfaceView，然后在Activity或者Fragment里面初始化

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
　　View rootView = inflater.inflate(R.layout.fragment_photo, container, false);
　　SurfaceView surfaceView = (SurfaceView) rootView.findViewById(R.id.surface);
　　surfaceView.getHolder().addCallback(this);
　　//此方法在API<11的手机上必须调用，否则没有效果
　　surfaceView.getHolder().setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
　　return rootView;
}

6、启动预览和Camera声明周期管理

    　　@Override
    　　public void surfaceCreated(SurfaceHolder holder) {
            mCamera = Camera.open();
            try {
                mCamera.setPreviewDisplay(holder);
            } catch (Exception e) {
                e.printStackTrace();
                return ;
            }
            setCameraDisplayOrientation(getActivity(), Camera.getNumberOfCameras()-1,mCamera);
            mCamera.startPreview();
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            mCamera.stopPreview();
            mCamera.release();
        }

7、拍照直接调用Camera.takePicture()即可。