android - 即时切换后置/前置摄像头

Question

如果我只使用 CAMERA_FACING_BACK 或 CAMERA_FACING_FRONT 一切正常。

我在从 CAMERA_FACING_BACK 切换到 CAMERA_FACING_FRONT 时遇到问题。

我的代码 fragment :

public class PhotoCameraActivity extends Activity implements OnClickListener {
private SurfaceView cameraView;
private Button turnButton;
private Camera camera = null;
private Callback listener;
private static int camId = Camera.CameraInfo.CAMERA_FACING_BACK;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.photo_camera_main);
    prepareActivity();
}

private void prepareActivity() {
    cameraView = (SurfaceView) findViewById(R.id.photo_camera_surface_view);

    turnButton = (ImageButton) findViewById(R.id.turn_button);
    turnButton.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    if (v.equals(turnButton)) {
        if (Camera.getNumberOfCameras() > 1 && camId < Camera.getNumberOfCameras() - 1) {
            startCamera(camId + 1);
        } else {
            startCamera(Camera.CameraInfo.CAMERA_FACING_BACK);
        }
    } 
}

@Override
protected void onResume() {
    startCamera(camId);
    super.onResume();
}

@Override
protected void onPause() {
    stopCamera();
    super.onPause();
}

private void startCamera(int cameraId) {
    if (camera != null) {
        stopCamera();
    }       
    holder = cameraView.getHolder();
    listener = new Callback() {

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
        }

        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            try {
                camera.setPreviewDisplay(holder);
                camera.startPreview();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int           width, int height) {}
    };
    holder.addCallback(listener);


    camId = cameraId;
    camera = Camera.open(cameraId);
    Camera.Parameters params = camera.getParameters();
    if (cameraId == Camera.CameraInfo.CAMERA_FACING_BACK) {
        params.setPreviewSize(1280, 800);
    } else {
        params.setPreviewSize(640, 480);
    }
    camera.setParameters(params);

}

private void stopCamera(){
    System.out.println("stopCamera method");
    if (camera != null){
        camera.stopPreview();
        camera.setPreviewCallback(null);
        camera.release();
        camera = null;
        holder.removeCallback(listener);
        holder = null;
    }
}

}

Answer 1

在我的 Activity 的 onCreate() 中，我将以下 onClick 监听器添加到覆盖在我的 Preview SurfaceView 上的按钮(网络上有许多示例用于预览):

ImageButton useOtherCamera = (ImageButton) findViewById(R.id.useOtherCamera);
//if phone has only one camera, hide "switch camera" button
if(Camera.getNumberOfCameras() == 1){
    useOtherCamera.setVisibility(View.INVISIBLE);
}
else {
    useOtherCamera.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
    if (inPreview) {
        camera.stopPreview();
    }
    //NB: if you don't release the current camera before switching, you app will crash
    camera.release();

    //swap the id of the camera to be used
    if(currentCameraId == Camera.CameraInfo.CAMERA_FACING_BACK){
        currentCameraId = Camera.CameraInfo.CAMERA_FACING_FRONT;
    }
    else {
        currentCameraId = Camera.CameraInfo.CAMERA_FACING_BACK;
    }
    camera = Camera.open(currentCameraId);
    //Code snippet for this method from somewhere on android developers, i forget where
    setCameraDisplayOrientation(CameraActivity.this, currentCameraId, camera);
    try {
        //this step is critical or preview on new camera will no know where to render to
        camera.setPreviewDisplay(previewHolder);
    } catch (IOException e) {
        e.printStackTrace();
    }
    camera.startPreview();
}

在我的测试设备上，后置摄像头的 ID 为 0，前置摄像头的 ID 为 1。我建议使用 Camera.CameraInfo 静态变量作为摄像头 ID，而不是硬编码值。我确信这只会在其他设备上引起问题。