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Android QR Code Scanner camera not opening in Fragment

I try to create QR Code scanner in fragment, but camera won't showing in surfaceview and just turn black.
here's my java class:
public class ScanFragment extends Fragment {
SurfaceView surfaceView;
CameraSource cameraSource;
TextView textView;
BarcodeDetector barcodeDetector;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_scan, container, false);
surfaceView = (SurfaceView) view.findViewById(R.id.cameraPreview);
textView = (TextView) view.findViewById(R.id.scanText);
barcodeDetector = new BarcodeDetector.Builder(view.getContext().getApplicationContext())
.setBarcodeFormats(Barcode.QR_CODE).build();
cameraSource = new CameraSource.Builder(view.getContext().getApplicationContext(), barcodeDetector)
.setRequestedPreviewSize(640, 480).build();
surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
#Override
public void surfaceCreated(SurfaceHolder holder) {
if (ActivityCompat.checkSelfPermission(getContext().getApplicationContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
return;
}
try {
cameraSource.start(holder);
}catch (IOException e){
e.printStackTrace();
}
}
#Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
#Override
public void surfaceDestroyed(SurfaceHolder holder) {
cameraSource.stop();
}
});
barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
#Override
public void release() {
}
#Override
public void receiveDetections(Detector.Detections<Barcode> detections) {
final SparseArray<Barcode> qrCodes = detections.getDetectedItems();
if(qrCodes.size() != 0){
textView.post(new Runnable() {
#Override
public void run() {
Vibrator vibrator = (Vibrator) getContext().getApplicationContext().getSystemService(Context.VIBRATOR_SERVICE);
vibrator.vibrate(1000);
textView.setText(qrCodes.valueAt(0).displayValue);
}
});
}
}
});
return view;
}
}
I gave the uses permissions from the android manifest file. compiles seamlessly in android studio but when I run it on the phone the camera just turn black and no crash from that.
Anyone know how to fix this?

From Android 6.0(API 23) on, you need to request runtime permission from the users. That is why your camera doesn't show anything. Permission is only defined in AndroidManifest, but the user did not agree to allow your application to use a camera. You have a good example of how to request runtime permissions here.
If you want to read more about this, there is also documentation available on Android developer:
https://developer.android.com/distribute/best-practices/develop/runtime-permissions
https://developer.android.com/training/permissions/requesting

How to make a method communicate with both an Activity and a Fragment?

I have an app consisting of (among other things) one Activity and one Fragment. In the Activity som data is displayed using TextViews, and in the Fragment the user can input some data using EditText-views. I have a method which takes data from both the Activity and Fragment, performs some calculations and finally displays a result in both the Fragment and the Activity. This method currently works when I call if after editing the text in any of the EditText-views in the Fragment. However, I also want to call it each time I update the data in the Activity but when I attempt this, I can not fetch the EditText data because they return null.
So my question is: what is good practice, or the ”right way” to do when dealing with methods that are supposed to be reached from both an Activity and a Fragment? I would greatly appreciate if someone could lead me onto the right track.
I have read the official documentation on Fragments and there ViewModel was mentioned. But this doesn’t seem suitable in for my application since I want the Activity to be involved. Do I need to use this or can I go through my main Activity? I’ve also read about Interfaces, but I’m not sure which one would suit my project best. I’m currently using Interfaces, but I’m not sure if I’m doing it correctly.
I’ve also watched this video and read these following questions:
Shared ViewModel to help communication between fragments and parent activity
Call a fragmentMethod from another fragment, but can't refer to them in parentFragmentActivity's View pager
how to manage the fragments in android correctly?
"My God"’s reply to this question was helpful but I’m still not sure what is the best thing to do in my case, as I have a Fragment where user can input data, and the same fragment should also view data as a result of that input. (Maybe my first mistake is building the app like this?)
I provide some code in case it is helpful.
public class AccuracyFragment extends Fragment {
EditText editTextLevel, editTextAccuracy;
private OnFragmentInteractionListener mListener;
public AccuracyFragment() {
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_accuracy, container, false);
editTextAccuracy = view.findViewById(R.id.text_accuracy_character);
editTextLevel = view.findViewById(R.id.text_level_character);
TextWatcher watcher = new TextWatcher() {
#Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
//Doing nothing
}
#Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
//Doing nothing
}
#Override
public void afterTextChanged(Editable editable) {
updateFragment(Float.valueOf(editTextLevel.getText().toString()), Float.valueOf(editTextAccuracy.getText().toString()));
}
};
editTextLevel.addTextChangedListener(watcher);
editTextAccuracy.addTextChangedListener(watcher);
return view;
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null; //I don’t know what this does
}
#Override
public void onResume() {
super.onResume();
// updateFragment(); //Should I have this?
}
public interface OnFragmentInteractionListener {
String[] onAccuracyFragmentInputChanged(float levelFromFragment, float accuracyFromFragment); }
public void updateFragment(float level, float accuracy) {
//Complicated method doing things with editTextLevel and editTextAccuracy. However, it doesn’t work when this method is called from outside AccuracyFragment – EditTexts are null
}
#Override
public void onDestroy() {
super.onDestroy();
}
#Override
public void onPause() {
super.onPause();
}
#Override
public void onDestroyView() {
super.onDestroyView();
}
#Override
public void onStop() {
super.onStop();
}
}
 
public class MainActivity extends AppCompatActivity implements AccuracyFragment.OnFragmentInteractionListener, AdapterView.OnItemSelectedListener {
AccuracyFragment accuracyFragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_new);
selectedID = null;
textView1 = (TextView) findViewById(R.id.text_1);
textView2 = (TextView) findViewById(R.id.text_2);
// Check that the activity is using the layout version with
// the fragment_container FrameLayout
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state, then we don't need to do anything and should return or else we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create a new Fragment to be placed in the activity layout
accuracyFragment = new AccuracyFragment();
}
}
//This is the core method which takes the value from two EditTexts in the Fragment, and two TextViews in the MainActivity
private String[] getRequiredAccuracy(float firstValueFromActivity, float secondValueFromActivity, float firstValueFromFragment, float secondValueFromFragment) {
//This methods uses parameters from the Activity, and two from the Fragment, and is intended to be called from both the Activity and from the Fragment itself
String returnValues[] = {s, q, r, c}; //This method is too complex to show, but it will end up outputting some values
return returnValues;
}
public void methodCalledUponClick(View view) {
//After showing a Dialog with some choices, I intend to call the method from fragment:
accuracyFragment.updateFragment();
}
#Override
public String[] onAccuracyFragmentInputChanged(float levelFromFragment, float accuracyFromFragment) {
String returnValues[] = {"0", "0", "0"};
if (selectedID != null) {
if (textView1.length() == 0 || textView2.length() == 0) {
//Do nothing if any of these are empty
} else {
returnValues = getRequiredAccuracy(Float.valueOf(textView1.getText().toString()), Float.valueOf(textView2.getText().toString()), levelFromFragment, accuracyFromFragment);
}
}
return returnValues;
}
}
}

You can go ahead with callback/Interface to communicate with fragment and activity simultaneously.
For Creating callback/Interface:
public interface CallBackListener {
void onCallBack(String value);// pass any parameter in your onCallBack which you want to return
}
In Fragment Class:
public class AccuracyFragment extends Fragment {
private CallBackListener callBackListener;
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
//getActivity() is fully created in onActivityCreated and instanceOf differentiate it between different Activities
if (getActivity() instanceof CallBackListener)
callBackListener = (CallBackListener) getActivity();
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
EditText editText = (EditText) view.findViewById(R.id.edittext);
editText.addTextChangedListener(new TextWatcher() {
#Override
public void afterTextChanged(Editable s) {}
#Override
public void beforeTextChanged(CharSequence s, int start,
int count, int after) {
}
#Override
public void onTextChanged(CharSequence s, int start,
int before, int count) {
if(callBackListener != null)
callBackListener.onCallBack(s.toString());
}
});
}
}
In your Activity:
public class MainActivity extends AppCompatActivity implements CallBackListener
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public void onCallBack(String value) {
Toast.makeText(mContext,"onCallback Called",Toast.LENGTH_LONG).show();
}
}

Parent Activity of a Fragment is NULL upon Square Receipt Payment Signature

I have a MasterActivity that has a few fragments. One fragment allows the user to open up Square to pay. After the user signs their name in Square and the data is returned to my app, my app crashes because the Payment fragment can't find the MasterActivity as it is null.
This only happens when the user signs the receipt. If the user pays cash (no signature) the My App works fine.
I have noticed that the when the Square App is ready for a signature it rotates the screen, just before the signature capture activity is view-able, I can see my app rotate too.
After the Square application has returned to my app, I can see the successful upload of the data to my server from my app. Then, it is only when the payment fragment asks the MasterActivity to refresh the data, I get a null pointer exception for the DISP_KEY in MasterAcitvity .
Can any see what I might be doing wrong?
MasterActivity
public class MasterActivity extends AppCompatActivity {
private String TAG = getClass().getSimpleName();
private String DISP_KEY = "";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_master);
Intent intent = getIntent();
DISP_KEY = (String) intent.getSerializableExtra("SELECTED_DISPATCH");
initView();
refreshData();
}
#Override
public void onBackPressed() {
super.onBackPressed();
}
public void refreshData() {
//Do some network download data stuff using the DISP_KEY
}
private void initView() {
TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
//JUST TEXT
tabLayout.addTab(tabLayout.newTab().setText("Details"));
tabLayout.addTab(tabLayout.newTab().setText("Sections"));
tabLayout.addTab(tabLayout.newTab().setText("Area"));
tabLayout.addTab(tabLayout.newTab().setText("Notes"));
tabLayout.addTab(tabLayout.newTab().setText("Payments"));
final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
final PagerAdapter adapter = new TabPagerAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(adapter);
}
}
PaymentFragment
public class PaymentFragment extends Fragment {
private static final int SQUARE_CHARGE_REQUEST_CODE = 1;
private String TAG = getClass().getSimpleName();
private PosClient posClient;
public PaymentFragment() {
// Required empty public constructor for fragments
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_payment, container, false);
initGUI(view);
return view;
}
#Override
public void onStart() {
super.onStart();
mVehicle = ((MasterActivity) this.getActivity()).getCurrentVehicle();
if (mVehicle != null) {
reloadData();
}
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (this != null) {
((MasterActivity) context).registerDataReloadListener(this);
posClient = PosSdk.createClient(getActivity(), AppConfig.SQUARE_APP_ID);
} else {
((MasterActivity) context).onBackPressed();
}
}
#Override
public void onDetach() {
super.onDetach();
if (this != null) {
((MasterActivity) getActivity()).unregisterDataReloadListener(this);
}
}
public void reloadData() {
//Ask the master activity to reload data
}
// SQUARE
private void acceptSquarePayment() {
ChargeRequest.TenderType types;
ChargeRequest request = new ChargeRequest.Builder(Integer.parseInt(square_balance), CurrencyCode.USD)
.enforceBusinessLocation(square_location_id)
.restrictTendersTo(types)
.requestMetadata(square_call_num)
.autoReturn(3200, TimeUnit.MILLISECONDS)
.build();
Intent intent = posClient.createChargeIntent(request);
startActivityForResult(intent, SQUARE_CHARGE_REQUEST_CODE);
}
// GET SQAURE RESULTS
#Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == Activity.RESULT_OK) {
ChargeRequest.Success success = posClient.parseChargeSuccess(data);
sendReceiptToAPIServer(success.serverTransactionId, success.clientTransactionId, success.requestMetadata);
}
}
private void sendReceiptToAPIServer(String serverTransactionId, String clientTransactionId, String callNum) {
//Do some data upload stuff
//After the successufull upload, this is where the crash happens
reloadData();
}
#Override
public void onDataReload() {
mVehicle = ((MasterActivity) this.getActivity()).getCurrentVehicle();
if (getView() != null) {
reloadData();
}
}
}

android calling a MainActivity function from a fragment

I'm new to android and I'm trying to get a hang of creating and using Fragments.
I have a fragment that shows a simple list of multiple dates to choose from and implements an onClickListener. The idea is once a user chooses a date, the fragments sends the date back to the MainActivity which then runs a query in database and sends the database response to another fragment.
I'm stuck on the point of sending the date back to MainActivity, elegantly. I can't find much info. I found this:
Activity activity = getActivity();
if(activity instanceof MyActivity){
MyActivity myactivity = (MyActivity) activity;
myactivity.myMethod();
}
I'm very new to this but this seems hacky to me. Is this the right way or is there another way?
Any input is appreciated

I prefer the interface based approach because is very clean. You can declare a nested interface in your Fragment or an external one:
interface OnMyStuffListener {
void myMethod();
}
Make the Activity to implement that interface:
public class MainActivity extends Activity implements OnMyStuffListener {
#Override
public void myMethod() {
// Do whatever you want.
}
}
The Fragment will be attached to the Activity so you can check the instance of the Context and cast it to the Activity:
public class MyFragment extends Fragment implements View.OnClickListener {
private OnMyStuffListener mListener;
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnMyStuffListener) {
mListener = (OnMyStuffListener) context;
} else {
throw new IllegalArgumentException("The context " + context.getClass().getName() +
"must implement " + OnMyStuffListener.class.getName());
}
}
#Override
public void onDetach() {
super.onDetach();
// Release it avoiding memory leak.
mListener = null;
}
#Override
public void onClick(View v) {
mListener.myMethod();
}
}

YES this is absolutely right. You can use this, if you are not sure that your Fragment is attached to Activity
You can also achieve this by using Interface, using an EventBus like LocalBroadcastManager, or starting a new Activity with an Intent and some form of flag passed into its extras Bundle or something else.
Here is an example about using Interface:
1. Add function sendDataToActivity() into the interface (EventListener).
//EventListener.java
public interface EventListener {
public void sendDataToActivity(String data);
}
2. Implement this functions in your MainActivity.
// MainActivity.java
public class MainActivity extends AppCompatActivity implements EventListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public void sendDataToActivity(String data) {
Log.i("MainActivity", "sendDataToActivity: " + data);
}
}
3. Create the listener in MyFragment and attach it to the Activity.
4. Finally, call function using listener.sendDataToActivity("Hello World!").
// MyFragment.java
public class MyFragment extends Fragment {
private EventListener listener;
#Override
public void onAttach(Activity activity)
{
super.onAttach(activity);
if(activity instanceof EventListener) {
listener = (EventListener)activity;
} else {
// Throw an error!
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_my, container, false);
// Send data
listener.sendDataToActivity("Hello World!");
return view;
}
#Override
public void onDetach() {
super.onDetach();
listener = null;
}
}
Hope this will help~

Is AsyncTask delivering any response between onDestroy() and onCreate() callbacks of a fragment?

I know I came a bit too late to the party and over the past 3 years (or maybe longer) there've been thousands and thousands of discussion like this one (unfortunately most of them involving activities and not fragments), but I'm curious about one thing.
Having the following piece of code, can mFragment be null when the AsyncTask's callback onError() or onSuccess() gets called after the screen orientation changes? So the AsyncTask starts, I rotate the screen of the device and at some point the AsyncTask will return an error or a success. When this happens, can the mFragment be null?
I already know that this cannot happen when dealing with Activities because basically no messages will be processed between a call to onRetainNonConfigurationInstance() of the previous instance and onCreate() of the new instance of the activity.
Unfortunately I couldn't find anything about this rule when it comes to fragments.
Do you guys know anything about this?
Thank you for your answers!
public class Fragment extends Fragment {
private WorkerFragment mWorkerFragment;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mWorkerFragment =(WorkerFragment)getFragmentManager().findFragmentByTag("worker_fragment");
if (mWorkerFragment == null) {
mWorkerFragment = new WorkerFragment();
getFragmentManager().beginTransaction().add(mWorkerFragment, "worker_fragment").commit();
}
if (savedInstanceState == null) {
mWorkerFragment.performAsyncTask();
}
private static class WorkerFragment extends Fragment {
private TypeOfAsyncTask mAsyncTask;
private Fragment mFragment;
private Callback mCallback = new Callback() {
#Override
public void onError(Error error) {
// Can mFragment be null here?
mFragment.onSendRequestError(error);
}
#Override
public void onSuccess(Result result) {
// Can mFragment be null here?
mFragment.onSendRequestSuccess(result);
}
};
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
mFragment = (Fragment) getTargetFragment();
}
#Override
public void onDetach() {
super.onDetach();
mFragment = null;
}
private void performAsyncTask() {
mAsyncTask = new TypeOfAsyncTask(mCallback);
mAsyncTask.execute();
}
}
}