我正在开发一款拥有Camera Preview Activity
的Android应用。它使用计时器每2秒调用takePicture()
并对PictureCallback
中捕获的图像进行一些处理。从Android文档中,我了解到PictureCallback
与Camera.open()
在同一个帖子中发生。
此外,建议在单独的帖子中调用takePicture()
。 What's the best way to call StartPreview() after an image is captured?
我希望每次捕获的处理都在不同的线程上进行,相机预览应该在主UI线程中继续。使用AsyncTask()
实现此目的的最佳方法是什么?
public class CameraActivity extends AppCompatActivity{
public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;
public static String TAG = "Exception";
int viewWidth = 0;
int viewHeight = 0;
private Camera mCamera;
private CameraPreview mPreview;
private ImageView iv;
private RelativeLayout rl;
private Camera.PictureCallback mPicture;
private MRZ_OCR mrz = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_camera);
rl = (RelativeLayout) findViewById(R.id.rel_camera);
iv = (ImageView) findViewById(R.id.black_above);
viewWidth = iv.getWidth();
viewHeight = rl.getHeight() - 2 * iv.getHeight();
// Create an instance of Camera
mCamera = getCameraInstance();
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
new Timer().schedule(new TimerTask() {
@Override
public void run() {
mCamera.startPreview();
mrz = new MRZ_OCR();
mrz.execute();
}
}, 4000, 4000);
mPicture = new Camera.PictureCallback() {
@Override
public void onPictureTaken(byte[] data, Camera camera) {
// Crop to get only MRZ
Bitmap bm = BitmapFactory.decodeByteArray(data, 0, data.length);
bm = Bitmap.createBitmap(bm, 0, pxFromDp(CameraActivity.this, 120), viewWidth, viewHeight);
//Verify if it has MRZ
bm = MRZ.getMRZ(bm);
if (bm != null) {
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bm.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] byteArray = stream.toByteArray();
createImageFile(byteArray);
Toast.makeText(getApplicationContext(), "Pic Saved", Toast.LENGTH_LONG).show();
}
}
};
}
@Override
protected void onPause() {
super.onPause();
releaseCamera(); // release the camera immediately on pause event
}
private void releaseCamera() {
if (mCamera != null) {
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
private class MRZ_OCR extends AsyncTask<Void, Void, Void>
{
private byte[] data;
@Override
protected Void doInBackground(Void... params) {
mCamera.takePicture(null, null, mPicture);
// Sleep for however long, you could store this in a variable and
// have it updated by a menu item which the user selects.
try {
Thread.sleep(3000); // 3 second preview
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
// This returns the preview back to the live camera feed
mCamera.startPreview();
}
}
public static int pxFromDp(final Context context, final float dp) {
return (int) (dp * context.getResources().getDisplayMetrics().density);
}
/**
* A safe way to get an instance of the Camera object.
*/
public static Camera getCameraInstance() {
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
} catch (Exception e) {
// Camera is not available (in use or does not exist)
}
return c; // returns null if camera is unavailable
}
private static File getOutputMediaFile(int type)
{
File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_PICTURES), "MyCameraApp");
// Create the storage directory if it does not exist
if (!mediaStorageDir.exists()) {
if (!mediaStorageDir.mkdirs()) {
Log.d("MyCameraApp", "failed to create directory");
return null;
}
}
// Create a media file name
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
File mediaFile;
if (type == MEDIA_TYPE_IMAGE) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"IMG_" + timeStamp + ".jpg");
} else if (type == MEDIA_TYPE_VIDEO) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"VID_" + timeStamp + ".mp4");
} else {
return null;
}
return mediaFile;
}
private static void createImageFile(byte[] byteArray) {
//create empty image type file
File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
if (pictureFile == null) {
Log.d(TAG, "Error creating media file, check storage permissions: ");
return;
}
try {
FileOutputStream fos = new FileOutputStream(pictureFile);
fos.write(byteArray);
fos.close();
} catch (FileNotFoundException e) {
Log.d(TAG, "File not found: " + e.getMessage());
} catch (IOException e) {
Log.d(TAG, "Error accessing file: " + e.getMessage());
}
}
}
答案 0 :(得分:0)
我不知道api takePicture()
,但我认为您需要做的是将此代码放在一个单独的主题中。
Bitmap bm = BitmapFactory.decodeByteArray(data, 0, data.length);
bm = Bitmap.createBitmap(bm, 0, pxFromDp(CameraActivity.this, 120), viewWidth, viewHeight);
//Verify if it has MRZ
bm = MRZ.getMRZ(bm);
if (bm != null) {
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bm.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] byteArray = stream.toByteArray();
createImageFile(byteArray);
}
decodeBitmap是一个耗时的过程,尤其是在你的app中,每2秒执行一次。它会阻塞主线程。以及为什么建议在一个单独的线程中调用takePicture(),我认为这是同样的原因。
答案 1 :(得分:0)
你已经回答了你的问题。将byte[] data
传递给AsyncTask:
private class PictureConverter extends AsyncTask<Void, Void, Void> {
private byte[] data;
private Camera camera;
public PictureConverter(byte[] _data, Camera _camera) {
data = _data;
camera = _camera;
}
protected Void doInBackground(Void... data) {
Camera.Parameters parameters = camera.getParameters();
ByteArrayOutputStream out = new ByteArrayOutputStream();
YuvImage yuvImage = new YuvImage(data, parameters.getPreviewFormat(), parameters.getPreviewSize().width, parameters.getPreviewSize().height, null);
yuvImage.compressToJpeg(new Rect(0, 0, parameters.getPreviewSize().width, parameters.getPreviewSize().height), 90, out);
byte[] imageBytes = out.toByteArray();
Bitmap bitmap = BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.length);
out.flush();
out.close();
//TODO save the image
return null;
}
protected void onProgressUpdate() {
}
protected void onPostExecute() {
//TODO report that the image got saved
}
}