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我正在开发具有Camera Preview Activity的Android应用程序。它使用计时器每2秒钟调用takePicture()，并在PictureCallback中对捕获的图像执行一些处理。从Android文档中，我了解到PictureCallback发生在与Camera.open()相同的线程中。相机预览Android
此外，建议在单独的线程中调用takePicture()。 What's the best way to call StartPreview() after an image is captured?
我希望每个捕获的处理都发生在单独的线程上，相机预览应该在主UI线程中继续。使用AsyncTask()执行此操作的最佳方法是什么？
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());
}
}
}