Android下Camera应用的开发

Android Development

Android下Camera应用的开发

tags：Android, Development

Android上的应用开发主要参考Google官方关于Camera的开发说明，其中包含了关于TakePicture和CaptureVideo的示例代码片段。

要点：必须使用Preview来实现capture picture或video

1. Camera

• SurfaceView和SurfaceHolder 需要Preview就需要一个SurfaceView来装Preivew的内容， 并通过SurfaceHolder来控制其中的内容
• Camrea.PictureCallback 需要处理拍照，则需要一个PictureCallback的实例。并实现OnPictureTaken方法。

2. 基本流程

2.1 创建一个实现了SurfaceHolderCallback的类CameraPreview

1. 在该SurfaceHolder中处理所有有关Preivew和Camera相关的事情。需要定义：

   • Camera的SingleInstance：管理Camera对象，及其拍照等Camera的功能
   • SurfaceHolder的实例，管理当前的Preview的SurfaceHolder
   • Camera.PictureCallback的对象，用来作为Camera.takePicture时的参数，takePicture之后的处理都需要在PictureCallback中处理。

2. 实现SurfaceHolder的回调--SurfaceHolderCallback，以便自动处理Holder发生变化的一些event。

具体代码如下：

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    public final String TAG = "CameraPreview";
    private Camera mCamera = null;
    private CameraUtil mCameraUtil;
    private SurfaceHolder mSurfaceHolder;
    private Camera.PictureCallback mPicture;
    CameraPreview(Context context){
        super(context);
        mCameraUtil = new CameraUtil(context);
        mSurfaceHolder = getHolder();
        mSurfaceHolder.addCallback(this);
        mSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        mPicture = new Camera.PictureCallback() {
            @Override
            public void onPictureTaken(byte[] data, Camera camera) {
                //process image data
                ...
                //start preview again
                camera.startPreview();
            }
        };
    }
    @Override
    public void surfaceChanged(SurfaceHolder surfaceHolder, int format, int w, int h){
        if(mSurfaceHolder.getSurface()==null){
            //preview surface doesnot exist
            return;
        }
        try {
            mCamera.stopPreview();
        }catch (Exception e){
            Log.i(TAG, "STOP preview ERROR:"+e.getMessage());
        }
        // set preview size and make any resize, rotate or
        // reformatting changes here
        try {
            mCamera.setPreviewDisplay(mSurfaceHolder);
            mCamera.startPreview();
        }catch (Exception e){
            Log.i(TAG, "start preview error: "+e.getMessage());
        }
    }
    @Override
    public void surfaceCreated(SurfaceHolder surfaceHolder){
        try {
            //open camera
            mCamera = mCameraUtil.getCameraInstance();
        }catch (Exception e){
            Log.i(TAG, "Camera open failed!"+ e.getMessage());
            return;
        }finally {
            if(mCamera == null) {
                Log.i(TAG, "open camera failed");
                return;
            }
        }
        try {
            //set preview
            mCamera.setPreviewDisplay(mSurfaceHolder);
            //start preview
            mCamera.startPreview();
        }catch (Exception e){
            Log.i(TAG, "error setting camera preview:"+e.getMessage());
        }
    }
    @Override
    public void surfaceDestroyed(SurfaceHolder surfaceHolder){
        mCamera.stopPreview();
        mCamera.release();
        mCamera = null;
        Log.i(TAG, "preview destroyed");
    }
    public void takePicture(){
        mCamera.takePicture(null,null, mPicture);
        Log.i(TAG, "picture taked!");
    }
    public Camera getCamera(){
        return mCamera;
    }
    ...
}

<需要注意>

• 按照示例程序，takePicture之后，界面会停留在拍照界面上，而不会自动的重新startPreview，这时候需要人工的在OnPictureTaken回调函数里边，加上startPreview:

mPicture = new Camera.PictureCallback() {
    @Override
    public void onPictureTaken(byte[] data, Camera camera){
        //image data process
        ...
        //start preview again
        mCamera.startPreview();
    }    
};

2.2 设置界面

1. 在需要显示Preview的Activity上创建一个Frame。

2. 并将继承了SurfaceView的CameraView绑定到Frame上。

   mCameraPreview = new CameraPreview(this);
   cameraFrame.addView(mCameraPreview);

3. 通过Button调用takePicture来拍照

   mCameraPreview.takePicture()