为什么我的相机在另一个活动开始后停止预览？

Question

在“我的相机应用程序”中，我使用以下代码打开图库：

Intent intent = new Intent(); 
intent.setType("image/*"); 
intent.setAction(Intent.ACTION_GET_CONTENT);// 
startActivityForResult(Intent.createChooser(intent, "Select Picture"),10); 

全部运行良好。但是当我从图库返回时，Android 相机没有显示预览。 为什么会出现这样的情况呢？我的代码有什么问题吗？

我的相机活动代码：

    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        Log.e(TAG, "onCreate");

        Bundle extras = getIntent().getExtras();

        getWindow().setFormat(PixelFormat.TRANSLUCENT);
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.main);
        mSurfaceView = (SurfaceView) findViewById(R.id.surface_camera);
        clickMe = (ImageButton)findViewById(R.id.clickme);
        flashBtn = (Button)findViewById(R.id.flashBtn);
        selectCamera = (Button)findViewById(R.id.selectCameraFace);
        sharePicture = (Button)findViewById(R.id.sharePicture);
        selectPicture = (ImageButton)findViewById(R.id.selectPicture);

        //mSurfaceView.setOnClickListener(this);
        flashBtn.setOnClickListener(this);
        selectCamera.setOnClickListener(this);
        sharePicture.setOnClickListener(this);
        selectPicture.setOnClickListener(this);

        clickMe.setOnClickListener(this);
        mSurfaceHolder = mSurfaceView.getHolder();
        mSurfaceHolder.addCallback(this);
        mSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
    }

    Camera.PictureCallback mPictureCallback = new Camera.PictureCallback() {
        public void onPictureTaken(byte[] imageData, Camera c) {

            if (imageData != null) {

                Intent mIntent = new Intent();

                StoreByteImage(mContext, imageData, 100, "ImageName");
                mCamera.startPreview();

                setResult(FOTO_MODE, mIntent);
                //finish();

            }
        }
    };

    protected void onResume() {
        Log.e(TAG, "onResume");
        super.onResume();
        if(mPreviewRunning)
        {
            mCamera.stopPreview();
        }

    }

    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }

    protected void onStop() {
        Log.e(TAG, "onStop");
        super.onStop();
        //mCamera.stopPreview();/////// Added Method
    }

    public void surfaceCreated(SurfaceHolder holder) {
        Log.e(TAG, "surfaceCreated");
        mCamera = Camera.open();
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setFlashMode(Camera.Parameters.FLASH_MODE_ON);
//      parameters.getSupportedColorEffects();
//      parameters.setColorEffect(parameters.EFFECT_NEGATIVE);
        mCamera.setParameters(parameters);
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        Log.e(TAG, "surfaceChanged");

        // XXX stopPreview() will crash if preview is not running
        if (mPreviewRunning) {
            mCamera.stopPreview();
        }

        Camera.Parameters p = mCamera.getParameters();
        p.setPreviewSize(w, h);
        mCamera.setParameters(p);
        try {
            mCamera.setPreviewDisplay(holder);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        mCamera.startPreview();
        mPreviewRunning = true;
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        Log.e(TAG, "surfaceDestroyed");
        mCamera.stopPreview();
        mPreviewRunning = false;
        mCamera.release();
    }

Answer 1

每次您的 Activity 暂停时，您都需要释放相机，以便其他人也可以使用相机..并在 onResume 调用中重新获取相机..

这是 onPause 的代码，其中 mCameraDev 是相机对象的句柄

@Override
protected void onPause() {
    Log.w(TAG, "OnPause()");

    if (null != mCameraDev) {
        mCameraDev.stopPreview();
        mCameraDev.release();
        mCameraDev = null;
    }
    super.onPause();

}

这里是 onResume 的代码

@Override
protected void onResume() {
    super.onResume();

    if (null != mCameraDev) {
            mCameraDev.startPreview();
            mIsPreviewing = true;
    } else {
        mCameraDev = android.hardware.Camera.open();

        try {
            mCameraDev.setPreviewDisplay(mSurfaceHolder);
        } catch (Throwable ex) {
            throw new RuntimeException("setPreviewDisplay failed", ex);
        }

        mIsPreviewing = true;
    }
}