Develop Reference

Data resets when bottom navigation views are clicked

I have a bottom navigation view on my weather app containing 3 panels(Today, hourly & Daily). My activity hosts 3 fragments for the 3 panels. Currently, if I search for any city on the today fragment, it gives the data for such cities. Now the problem is that if I click on any bottom nav view(down), it resets the data displayed on the today fragment.
Here is an illustration of the issue:
Data is displayed after a city is searched(the part with a red tick):
Data goes on reset after clicking these bottom nav views(the part with a red tick):
I want the data to remain intact irrespective of clicking those nav views.
I tried using https://stackoverflow.com/a/60201555/16020235 suggestion. But it failed with this
exception:
java.lang.IllegalArgumentException: No view found for id 0x7f0a0116 (com.viz.lightweatherforecast:id/my_nav) for fragment ThirdFragment{90bc0de} (8e129d17-010d-41dc-9311-82e273b4e522 id=0x7f0a0116 tag=3)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:513)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2100)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3134)
at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3068)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:501)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:210)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
at android.app.Activity.performStart(Activity.java:7157)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3037)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1861)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6819)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:497)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:912)
I/weatherforecas: Compiler allocated 4MB to compile void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
I find it hard to implement his code and the remaining suggestions on that question are written in kotlin.
Please how can I resolve this?
Here are my codes:
my_nav.xml(navigation layout):
<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/my_nav"
app:startDestination="#id/firstFragment">
<fragment
android:id="#+id/firstFragment"
android:name="com.viz.lightweatherforecast.FirstFragment"
android:label="fragment_first"
tools:layout="#layout/fragment_first" />
<fragment
android:id="#+id/secondFragment"
android:name="com.viz.lightweatherforecast.SecondFragment"
android:label="fragment_second"
tools:layout="#layout/fragment_second" />
<fragment
android:id="#+id/thirdFragment"
android:name="com.viz.lightweatherforecast.ThirdFragment"
android:label="fragment_third"
tools:layout="#layout/fragment_third" />
</navigation>
activity_home.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/layout"
android:background="#drawable/dubai"
tools:context=".Activity.HomeActivity">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/bottomNavigationView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#FFFFFF"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:menu="#menu/bottom_menu" />
<androidx.fragment.app.FragmentContainerView
android:id="#+id/fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="409dp"
android:layout_height="599dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="#+id/bottomNavigationView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:navGraph="#navigation/my_nav"
/>
</androidx.constraintlayout.widget.ConstraintLayout>
HomeActivity:
public class HomeActivity extends AppCompatActivity {
// Last update time, click sound, search button, search panel.
TextView time_field;
MediaPlayer player;
ImageView Search;
EditText textfield;
// For scheduling background image change(using constraint layout, start counting from dubai, down to statue of liberty.
ConstraintLayout constraintLayout;
public static int count=0;
int[] drawable =new int[]{R.drawable.dubai,R.drawable.central_bank_of_nigeria,R.drawable.eiffel_tower,R.drawable.hong_kong,R.drawable.statue_of_liberty};
Timer _t;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
// use home activity layout.
time_field = findViewById(R.id.textView9);
Search = findViewById(R.id.imageView4);
textfield = findViewById(R.id.textfield);
// find the id's of specific variables.
BottomNavigationView bottomNavigationView = findViewById(R.id.bottomNavigationView);
// host 3 fragments along with bottom navigation.
final NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment);
assert navHostFragment != null;
final NavController navController = navHostFragment.getNavController();
NavigationUI.setupWithNavController(bottomNavigationView, navController);
// For scheduling background image change
constraintLayout = findViewById(R.id.layout);
constraintLayout.setBackgroundResource(R.drawable.dubai);
_t = new Timer();
_t.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
// run on ui thread
runOnUiThread(() -> {
if (count < drawable.length) {
constraintLayout.setBackgroundResource(drawable[count]);
count = (count + 1) % drawable.length;
}
});
}
}, 5000, 5000);
Search.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// make click sound when search button is clicked.
player = MediaPlayer.create(HomeActivity.this, R.raw.click);
player.start();
getWeatherData(textfield.getText().toString().trim());
// make use of some fragment's data
FirstFragment firstFragment = (FirstFragment) navHostFragment.getChildFragmentManager().getFragments().get(0);
firstFragment.getWeatherData(textfield.getText().toString().trim());
}
});
}
});
}
}
EDIT
Fragment class:
public class FirstFragment extends Fragment {
// User current time, current temperature, current condition, sunrise, sunset, temperature, pressure, humidity, wind_speed, visibility, clouds
TextView current_temp, current_output, rise_time, set_time, temp_out, Press_out, Humid_out, Ws_out, Visi_out, Cloud_out;
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
public FirstFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* #param param1 Parameter 1.
* #param param2 Parameter 2.
* #return A new instance of fragment SecondFragment.
*/
// TODO: Rename and change types and number of parameters
public static FirstFragment newInstance(String param1, String param2) {
FirstFragment fragment = new FirstFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_first, container, false);
// For displaying weather data
current_temp = rootView.findViewById(R.id.textView10);
current_output = rootView.findViewById(R.id.textView11);
rise_time = rootView.findViewById(R.id.textView25);
set_time = rootView.findViewById(R.id.textView26);
temp_out = rootView.findViewById(R.id.textView28);
Press_out = rootView.findViewById(R.id.textView29);
Humid_out = rootView.findViewById(R.id.textView30);
Ws_out = rootView.findViewById(R.id.textView33);
Visi_out = rootView.findViewById(R.id.textView34);
Cloud_out = rootView.findViewById(R.id.textView35);
return rootView;
}
public void getWeatherData(String name) {
ApiInterface apiInterface = ApiClient.getClient().create(ApiInterface.class);
Call<Example> call = apiInterface.getWeatherData(name);
call.enqueue(new Callback<Example>() {
#Override
public void onResponse(#NonNull Call<Example> call, #NonNull Response<Example> response) {
try {
assert response.body() != null;
current_temp.setVisibility(View.VISIBLE);
current_temp.setText(response.body().getMain().getTemp() + " ℃");
current_output.setVisibility(View.VISIBLE);
current_output.setText(response.body().getWeather().get(0).getDescription());
rise_time.setVisibility(View.VISIBLE);
rise_time.setText(response.body().getSys().getSunrise() + " ");
set_time.setVisibility(View.VISIBLE);
set_time.setText(response.body().getSys().getSunset() + " ");
temp_out.setVisibility(View.VISIBLE);
temp_out.setText(response.body().getMain().getTemp() + " ℃");
Press_out.setVisibility(View.VISIBLE);
Press_out.setText(response.body().getMain().getPressure() + " hpa");
Humid_out.setVisibility(View.VISIBLE);
Humid_out.setText(response.body().getMain().getHumidity() + " %");
Ws_out.setVisibility(View.VISIBLE);
Ws_out.setText(response.body().getWind().getSpeed() + " Km/h");
Visi_out.setVisibility(View.VISIBLE);
Visi_out.setText(response.body().getVisibility() + " m");
Cloud_out.setVisibility(View.VISIBLE);
Cloud_out.setText(response.body().getClouds().getAll() + " %");
} catch (Exception e) {
Log.e("TAG", "No City found");
current_temp.setVisibility(View.GONE);
current_output.setVisibility(View.GONE);
rise_time.setVisibility(View.GONE);
set_time.setVisibility(View.GONE);
temp_out.setVisibility(View.GONE);
Press_out.setVisibility(View.GONE);
Humid_out.setVisibility(View.GONE);
Ws_out.setVisibility(View.GONE);
Visi_out.setVisibility(View.GONE);
Cloud_out.setVisibility(View.GONE);
Toast.makeText(getActivity(), "No City found", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onFailure(#NotNull Call<Example> call, #NotNull Throwable t) {
t.printStackTrace();
}
});
}
}
I didn't paste everything because I'm following https://stackoverflow.com/help/minimal-reproducible-example

Your problem is that your FirstFragment is not saving its state properly. As per the Saving state with fragments guide:
To ensure the user's state is saved, the Android framework automatically saves and restores the fragments and the back stack. Therefore, you need to ensure that any data in your fragment is saved and restored as well.
But you aren't saving the last name that you pass to getWeatherData, nor are you saving your Example object that you get from your API call in order to repopulate your views when they are recreated.
So need to actually use the APIs described in that guide to save your state. Namely, you should file the Guide to app architecture, which explains how you can separate your from your data loading by using ViewModels to store data across configuration changes (like rotating your device) and LiveData to automatically populate your UI whenever your data is loaded.
The first thing we want to do is move the data loading to a ViewModel. This object survives configuration changes which means any data stored in this class is automatically saved when you rotate your device. This is how we can save your Example class and avoid calling the server over and over.
By using the APIs in the Saved State module for ViewModel (specifically, the SavedStateHandle class), any data you save in there will survive your process being killed and later recreated (say, if your device is low on memory, etc.). This is how we can save the last name so that we will automatically requery for your data.
Here, our ViewModel handles all of the loading from the server and uses a LiveData to let our UI automatically update as the data is loaded.
public class WeatherDataViewModel extends ViewModel {
// This will save the city name
private SavedStateHandle state;
// This is where we'll store our result from the server
private MutableLiveData<Example> mutableWeatherData = new MutableLiveData<>();
public WeatherDataViewModel(SavedStateHandle savedStateHandle) {
state = savedStateHandle;
String savedCityName = state.get("name");
if (savedCityName != null) {
// We already had a previously saved name, so we'll
// start loading right away
loadData();
}
}
// This is what our Fragment will use to get the latest weather data
public LiveData<Example> getWeatherDataLiveData() {
return mutableWeatherData;
}
// When you get a new city name, we'll save that in our
// state, then load the new data from the server
public void setCityName(String name) {
state.set("name", name);
loadData();
}
private void loadData() {
// Get the last name that was set
String name = state.get("name");
// Now kick off a load from the server
ApiInterface apiInterface = ApiClient.getClient().create(ApiInterface.class);
Call<Example> call = apiInterface.getWeatherData(name);
call.enqueue(new Callback<Example>() {
#Override
public void onResponse(#NonNull Call<Example> call, #NonNull Response<Example> response) {
// Save the response we've gotten
// This will automatically update our UI
mutableWeatherData.setValue(response.body());
}
#Override
public void onFailure(#NotNull Call<Example> call, #NotNull Throwable t) {
t.printStackTrace();
}
});
}
}
Now you can rewrite your FirstFragment to use the WeatherDataViewModel as the source of truth for your UI:
public class FirstFragment extends Fragment {
private WeatherDataViewModel viewModel;
public FirstFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_first, container, false);
// For displaying weather data
final TextView current_temp = rootView.findViewById(R.id.textView10);
final TextView current_output = rootView.findViewById(R.id.textView11);
final TextView rise_time = rootView.findViewById(R.id.textView25);
final TextView set_time = rootView.findViewById(R.id.textView26);
final TextView temp_out = rootView.findViewById(R.id.textView28);
final TextView Press_out = rootView.findViewById(R.id.textView29);
final TextView Humid_out = rootView.findViewById(R.id.textView30);
final TextView Ws_out = rootView.findViewById(R.id.textView33);
final TextView Visi_out = rootView.findViewById(R.id.textView34);
final TextView Cloud_out = rootView.findViewById(R.id.textView35);
// Get our ViewModel instance
viewModel = new ViewModelProvider(this).get(WeatherDataViewModel.class);
// And whenever the data changes, refresh the UI
viewModel.getWeatherDataLiveData().observe(getViewLifecycleOwner(), data -> {
if (data != null) {
current_temp.setVisibility(View.VISIBLE);
current_temp.setText(data.getMain().getTemp() + " ℃");
current_output.setVisibility(View.VISIBLE);
current_output.setText(data.getWeather().get(0).getDescription());
rise_time.setVisibility(View.VISIBLE);
rise_time.setText(data.getSys().getSunrise() + " ");
set_time.setVisibility(View.VISIBLE);
set_time.setText(data.getSys().getSunset() + " ");
temp_out.setVisibility(View.VISIBLE);
temp_out.setText(data.getMain().getTemp() + " ℃");
Press_out.setVisibility(View.VISIBLE);
Press_out.setText(data.getMain().getPressure() + " hpa");
Humid_out.setVisibility(View.VISIBLE);
Humid_out.setText(data.getMain().getHumidity() + " %");
Ws_out.setVisibility(View.VISIBLE);
Ws_out.setText(data.getWind().getSpeed() + " Km/h");
Visi_out.setVisibility(View.VISIBLE);
Visi_out.setText(data.getVisibility() + " m");
Cloud_out.setVisibility(View.VISIBLE);
Cloud_out.setText(data.getClouds().getAll() + " %");
} else {
Log.e("TAG", "No City found");
current_temp.setVisibility(View.GONE);
current_output.setVisibility(View.GONE);
rise_time.setVisibility(View.GONE);
set_time.setVisibility(View.GONE);
temp_out.setVisibility(View.GONE);
Press_out.setVisibility(View.GONE);
Humid_out.setVisibility(View.GONE);
Ws_out.setVisibility(View.GONE);
Visi_out.setVisibility(View.GONE);
Cloud_out.setVisibility(View.GONE);
Toast.makeText(requireActivity(), "No City found", Toast.LENGTH_SHORT).show();
}
});
return rootView;
}
public void getWeatherData(String name) {
// The ViewModel controls loading the data, so we just
// tell it what the new name is - this kicks off loading
// the data, which will automatically call through to
// our observe() call when the data load completes
viewModel.setCityName(name);
}
}
With these changes, you'll find that your Fragment now correctly handles:
Being put on the Fragment back stack
Configuration changes (i.e., rotating your device)
Process death and recreation (i.e., testing with 'Don't keep activities' on)
You'll note how we use new ViewModelProvider(this).get(WeatherDataViewModel.class) - that creates a WeatherDataViewModel that is tied to this - your Fragment itself. This is best if the data your ViewModel loads is only used in that one Fragment.
If you also wanted to use this same data in your Activity, your activity could use new ViewModelProvider(this).get(WeatherDataViewModel.class) to create a WeatherDataViewModel that is scoped to the entire Activity. Any Fragment could then use new ViewModelProvider(requireActivity()).get(WeatherDataViewModel.class) to get that Activity owned ViewModel. This would potentially mean that you wouldn't need a getWeatherData() method on your Fragment at all - instead, your Activity would directly call viewModel.setCityName(name) itself and all Fragments would just instantly update (as they read from the same ViewModel).

I think, this is because your FirstFragment gets reinstantiated every time. To save state, modify onCreate() of your FirstFragment like following:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState != null) {
mParam1 = savedInstanceState.getString(ARG_PARAM1);
mParam2 = savedInstanceState.getString(ARG_PARAM2);
} else if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
And add onSaveInstanceState() to your FirstFragment:
#Override
public void onSaveInstanceState(#NonNull Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString(ARG_PARAM1, mParam1);
outState.putString(ARG_PARAM2, mParam2);
}

The mistake seems to be that every time you select an item in the bottom navigation bar the fragment gets re-instantized thus creating a new fragment(of same type, but a new object of that fragment).
I would suggest you create an object of all the fragment at the start like this
private final Fragment[] fragments = {
new HomeFragment(),
new MyNotesFragment(),
new PreferencesFragment()
};
and then for the Bottom Nav Listener part, we will change the fragments according to the button clicked by passing already made instances of fragments rather than creating new ones.
bottom_navigation_view.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
// Checking which bottom_nav items is clicked by comparing with string names..
if (item.getTitle().toString().equals("Home")) {
// Code to change the fragments
final FragmentTransaction ft =
getFragmentManager().beginTransaction();
// we passed the already made instance of the home fragment rather than creating a new one
ft.replace(R.id.my_fragment, fragments[0], "HomeFrag");
ft.commit();
} else if (item.getTitle().toString().equals("My Notes")) {
// Code to change the fragments
final FragmentTransaction ft =
getFragmentManager().beginTransaction();
ft.replace(R.id.my_fragment, fragments[1], "MyNotesFrag");
ft.commit();
} else if (item.getTitle().toString().equals("Preferences")) {
// Code to change the fragments
final FragmentTransaction ft =
getFragmentManager().beginTransaction();
ft.replace(R.id.my_fragment, fragments[2], "PrefFrag");
ft.commit();
}
return true;
}
});
(Though this is for the ViewPager library the concept works the same)

If you still have not solve it yet, you might want to try this solution that uses SharedPreferences.
public class FirstFragment extends Fragment
{
// ...
private SharedPreferences prefs;
private SharedPreferences.Editor prefsEditor;
// ...
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_first, container, false);
// For displaying weather data
current_temp = rootView.findViewById(R.id.textView10);
current_output = rootView.findViewById(R.id.textView11);
// ...
prefs = new SharedPreferences(getActivity().getApplicationContext());
prefsEditor = prefs.edit();
current_temp.setText(prefs.getString("current_temp", "not yet initialised"));
current_output.setText(prefs.getString("current_output", "not yet initialised"));
// ...
return rootView;
}
public void getWeatherData(String name)
{
ApiInterface apiInterface = ApiClient.getClient().create(ApiInterface.class);
Call<Example> call = apiInterface.getWeatherData(name);
call.enqueue(new Callback<Example>() {
#Override
public void onResponse(#NonNull Call<Example> call, #NonNull Response<Example> response) {
try {
assert response.body() != null;
final String currentTemp = response.body().getMain().getTemp() + " ℃";
editor.putString("current_temp", currentTemp);
editor.commit();
current_temp.setText(currentTemp);
current_temp.setVisibility(View.VISIBLE);
final String currentOutput = response.body().getWeather().get(0).getDescription();
editor.putString("current_output", currentOutput);
editor.commit();
current_output.setText(currentOutput);
current_output.setVisibility(View.VISIBLE);
// ...
} catch (Exception e) {
Log.e("TAG", "No City found");
current_temp.setVisibility(View.GONE);
current_output.setVisibility(View.GONE);
// ...
Toast.makeText(getActivity(), "No City found", Toast.LENGTH_SHORT).show();
}
}
// ...
});
}
}

Undo deleted item from RecyclerView and Firebase

After removing the item from the Realtime Database and RecyclerView, I wish to add an UNDO function to recover the deleted item just now. May I know how to achieve it?
Below is my source code in Adapter class:
public Adapter(#NonNull FirebaseRecyclerOptions options) {
super(options);
}
#NonNull
#Override
public MyViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate
(R.layout.retrieved_layout,parent,false);
return new MyViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull MyViewHolder holder, int position, #NonNull Model model) {
holder.name.setText(model.getTask());
holder.date.setText(model.getDate());
}
public static class MyViewHolder extends RecyclerView.ViewHolder {
TextView name = itemView.findViewById(R.id.taskTv);
TextView date = itemView.findViewById(R.id.dateTv);
public MyViewHolder(#NonNull View itemView) {
super(itemView);
}
}
And here is my MainActivity:
recyclerView = findViewById(R.id.recyclerview);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setHasFixedSize(true);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
linearLayoutManager.setReverseLayout(true);
linearLayoutManager.setStackFromEnd(true);
loader = new ProgressDialog(this);
mAuth = FirebaseAuth.getInstance();
onlineUserID = mAuth.getCurrentUser().getUid();
reference = FirebaseDatabase.getInstance().getReference().child("task").child(onlineUserID);
add = findViewById(R.id.add);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
addTask();
}
});
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(simpleCallback);
itemTouchHelper.attachToRecyclerView(recyclerView);
// add task to recycler view
FirebaseRecyclerOptions<Model> options = new FirebaseRecyclerOptions.Builder<Model>()
.setQuery(reference, Model.class)
.build();
adapter = new Adapter(options);
}
// add task to real time database
private void addTask() {
AlertDialog.Builder myDialog = new AlertDialog.Builder(this);
LayoutInflater inflater = LayoutInflater.from(this);
View view = inflater.inflate(R.layout.input, null);
myDialog.setView(view);
AlertDialog dialog = myDialog.create();
final EditText task = view.findViewById(R.id.taskName);
ImageView upload = view.findViewById(R.id.upload);
upload.setOnClickListener((v) -> {
String mTask = task.getText().toString().trim();
String id = reference.push().getKey();
String date = DateFormat.getDateInstance().format(new Date());
if(TextUtils.isEmpty(mTask)){
task.setError("Task name required");
return;
}
else {
loader.setMessage("Adding your data");
loader.setCanceledOnTouchOutside(false);
loader.show();
Model model = new Model(mTask,id,date);
reference.child(id).setValue(model).addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
if(task.isSuccessful()) {
Toast.makeText(MainActivity.this, "Task added successfully !", Toast.LENGTH_SHORT).show();
loader.dismiss();
}
}
});
}
dialog.dismiss();
});
dialog.show();
}
// add task to recycler view
#Override
protected void onStart() {
super.onStart();
recyclerView.setAdapter(adapter);
adapter.startListening();
}
// swipe to delete task
ItemTouchHelper.SimpleCallback simpleCallback = new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT) {
#Override
public boolean onMove(#NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder, #NonNull RecyclerView.ViewHolder target) {
return false;
}
#Override
public void onSwiped(#NonNull RecyclerView.ViewHolder viewHolder, int direction) {
if (direction == ItemTouchHelper.LEFT) {
reference.child(key).removeValue();
Snackbar.make(recyclerView,"Task deleted", Snackbar.LENGTH_SHORT)
.setAction("Undo", new View.OnClickListener() {
#Override
public void onClick(View v) {
}
})
.show();
}
}

#Eyosiyas's answer will work but it has a downside. If you want to get all children of a node where the property "isActive" holds the value of true, it will work perfectly fine. However, if you need to add another filter, for example, to filter the data according to a "time" property, this won't work, because the Firebase Realtime Database does not support queries on multiple properties.
What options do you have?
You can perform the delete operation, and if the user clicks on an "UNDO" button, write the data back. It's not the best solution, as it implies a delete operation followed by a write operation. Or you can simulate the delete operation. How? When the user clicks on the delete button, don't perform the actual delete operation. Wait to see if the user clicks "UNDO". If the user clicks "UNDO" don't delete anything, otherwise, delete the element.

If you delete it from the real-time database then it is gone.
If you want to achieve the undo functionality, I suggest you create another value isActive.
Then when the user deletes you simply change isActive to false and don't show that data.
If the user wants the data back you simply change isActive to true and the data is back.
So the overall process is that you don't actually delete the data but you deactivate it.

Eyosiyas's answer is correct but you can delete the item after undo option is no longer available. Let's say you have a field in your data model named 'deleted' and when user removes the item, you set it to true. At this point all selects from database should exclude items flagged as deleted. I noticed you show a SnackBar with undo action. When undo is clicked you should set deleted back to false and when SnackBar is dismissed you can actually delete item from database (because there is no way user can redo deletion without SnackBar and its action being available).
// Set 'deleted' to true in database
snackbar = Snackbar.make(
binding.root,
getString(R.string.item_deleted),
Snackbar.LENGTH_LONG
).setAction(getString(R.string.undo)) {
// Set 'deleted' back to false in database
}.addCallback(object : Snackbar.Callback() {
override fun onDismissed(transientBottomBar: Snackbar, event: Int) {
if (event != DISMISS_EVENT_ACTION)
// Delete item from database
}
}).setDuration(5000)
snackbar.show()

How I can Remove NullpointerException in this case? [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 3 years ago.
I am using firebase database and want to show data in a listview.When I call onDataChange() of firebase database it shows nullpointer excetion. I find my best on google and many other sites but nothing helps me to get rid of this error, so please help me, I,m stuck on this error from last three hours...
Here is Mainactiviy named as Articles_from_firebase.java:
public class Articles_from_fireabse extends AppCompatActivity {
EditText editTextName;
Spinner spinnerGenre;
Button buttonAddArtist;
ListView listViewArtists;
DatabaseReference databaseArtists;
//a list to store all the artist from firebase database
List<Artist> artists;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_articles_from_fireabse);
databaseArtists = FirebaseDatabase.getInstance().getReference("artists");
editTextName = (EditText) findViewById(R.id.editTextName);
spinnerGenre = (Spinner) findViewById(R.id.spinnerGenres);
listViewArtists = (ListView) findViewById(R.id.listViewArtists);
buttonAddArtist = (Button) findViewById(R.id.buttonAddArtist);
buttonAddArtist.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//calling the method addArtist()
//the method is defined below
//this method is actually performing the write operation
addArtist();
}
});
}
private void addArtist() {
//getting the values to save
String name = editTextName.getText().toString().trim();
String genre = spinnerGenre.getSelectedItem().toString();
//checking if the value is provided
if (!TextUtils.isEmpty(name)) {
//getting a unique id using push().getKey() method
//it will create a unique id and we will use it as the Primary Key for our Artist
String id = databaseArtists.push().getKey();
//creating an Artist Object
Artist artist = new Artist(id, name, genre);
//Saving the Artist
databaseArtists.child(id).setValue(artist);
//setting edittext to blank again
editTextName.setText("");
//displaying a success toast
Toast.makeText(this, "Artist added", Toast.LENGTH_LONG).show();
} else {
//if the value is not given displaying a toast
Toast.makeText(this, "Please enter a name", Toast.LENGTH_LONG).show();
}
}
#Override
protected void onStart() {
super.onStart();
//attaching value event listener
databaseArtists.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//clearing the previous artist list
artists.clear();
//iterating through all the nodes
for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
//getting artist
Artist artist = postSnapshot.getValue(Artist.class);
//adding artist to the list
artists.add(artist);
}
//creating adapter
ArtistList artistAdapter = new ArtistList(Articles_from_fireabse.this, artists);
//attaching adapter to the listview
listViewArtists.setAdapter(artistAdapter);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
Here is my 2nd class ArtistList.java :
public class ArtistList extends ArrayAdapter<Artist> {
private Activity context;
List<Artist> artists;
public ArtistList(Activity context, List<Artist> artists) {
super(context, R.layout.list_layout, artists);
this.context = context;
this.artists = artists;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = context.getLayoutInflater();
View listViewItem = inflater.inflate(R.layout.list_layout, null, true);
TextView textViewName = (TextView) listViewItem.findViewById(R.id.textViewName);
TextView textViewGenre = (TextView) listViewItem.findViewById(R.id.textViewGenre);
Artist artist = artists.get(position);
textViewName.setText(artist.getArtistName());
textViewGenre.setText(artist.getArtistGenre());
return listViewItem;
}
This is my Stacktrace:
java.lang.NullPointerException
at com.example.e_agriculture10.Articles_from_fireabse$2.onDataChange(Articles_from_fireabse.java:92)
at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database##19.1.0:75)
This is the critical block of my code where error exists.
public void onDataChange(DataSnapshot dataSnapshot) {
//clearing the previous artist list
artists.clear();
//iterating through all the nodes
for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
//getting artist
Artist artist = postSnapshot.getValue(Artist.class);
//adding artist to the list
artists.add(artist);
}
//creating adapter
ArtistList artistAdapter = new ArtistList(Articles_from_fireabse.this, artists);
//attaching adapter to the listview
listViewArtists.setAdapter(artistAdapter);
}
According to my opinion in this line [artists.clear()], artists getting the null value. Why artists getting null value?

Easy Solution
Whenever you call artists.clear(); check to make sure it is not null.
if(artists != null)
artists.clear();
else
artists = new ArrayList<>();
Sustainable Solution
You should consider what the role of the artists object arry is. In this case, you have both a database and an array that both store information about artists. The database should store persistent data, that is data that lives after program execution. Whereas, your artists object is just around during runtime.
Therefore, you should have code at the start of your program that loads in data from the database into the artists object. Reference / edit / add to the artist object during runtime. Finally, have cleanup code at the end of runtime that updates the artist table in the database.

yes initialize List artists; inside onCreate(){}
Something like this
artists = new ArrayList<>();

Placing "Native Advanced Ads" inside popup close

I try to put advanced ads inside the dialog box when you close the application, but when you open a dialog box does not load the ad for the first time. ... I am worried that I load the ad inside the application
without appearing and at closing I put it in the dialog box for fear that the agent considers it a google violation to download the ad without its appearance
Constant code from android developer
public class MainActivity extends AppCompatActivity {
private static final String ADMOB_AD_UNIT_ID = "ca-app-pub-3940256099942544/2247696110";
private static final String ADMOB_APP_ID = "ca-app-pub-3940256099942544~3347511713";
AdLoader.Builder builder;
UnifiedNativeAdView adView;
private Button refresh;
private CheckBox startVideoAdsMuted;
private TextView videoStatus;
private UnifiedNativeAd nativeAd;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initialize the Mobile Ads SDK.
MobileAds.initialize(this, ADMOB_APP_ID);
refresh = findViewById(R.id.btn_refresh);
startVideoAdsMuted = findViewById(R.id.cb_start_muted);
videoStatus = findViewById(R.id.tv_video_status);
refresh.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View unusedView) {
refreshAd();
}
});
refreshAd();
}
/**
* Populates a {#link UnifiedNativeAdView} object with data from a given
* {#link UnifiedNativeAd}.
*
* #param nativeAd the object containing the ad's assets
* #param adView the view to be populated
*/
private void populateUnifiedNativeAdView(UnifiedNativeAd nativeAd, UnifiedNativeAdView adView) {
// Set the media view. Media content will be automatically populated in the media view once
// adView.setNativeAd() is called.
MediaView mediaView = adView.findViewById(R.id.ad_media);
adView.setMediaView(mediaView);
// Set other ad assets.
adView.setHeadlineView(adView.findViewById(R.id.ad_headline));
adView.setBodyView(adView.findViewById(R.id.ad_body));
adView.setCallToActionView(adView.findViewById(R.id.ad_call_to_action));
adView.setIconView(adView.findViewById(R.id.ad_app_icon));
adView.setPriceView(adView.findViewById(R.id.ad_price));
adView.setStarRatingView(adView.findViewById(R.id.ad_stars));
adView.setStoreView(adView.findViewById(R.id.ad_store));
adView.setAdvertiserView(adView.findViewById(R.id.ad_advertiser));
// The headline is guaranteed to be in every UnifiedNativeAd.
((TextView) adView.getHeadlineView()).setText(nativeAd.getHeadline());
// These assets aren't guaranteed to be in every UnifiedNativeAd, so it's important to
// check before trying to display them.
if (nativeAd.getBody() == null) {
adView.getBodyView().setVisibility(View.INVISIBLE);
} else {
adView.getBodyView().setVisibility(View.VISIBLE);
((TextView) adView.getBodyView()).setText(nativeAd.getBody());
}
if (nativeAd.getCallToAction() == null) {
adView.getCallToActionView().setVisibility(View.INVISIBLE);
} else {
adView.getCallToActionView().setVisibility(View.VISIBLE);
((Button) adView.getCallToActionView()).setText(nativeAd.getCallToAction());
}
if (nativeAd.getIcon() == null) {
adView.getIconView().setVisibility(View.GONE);
} else {
((ImageView) adView.getIconView()).setImageDrawable(
nativeAd.getIcon().getDrawable());
adView.getIconView().setVisibility(View.VISIBLE);
}
if (nativeAd.getPrice() == null) {
adView.getPriceView().setVisibility(View.INVISIBLE);
} else {
adView.getPriceView().setVisibility(View.VISIBLE);
((TextView) adView.getPriceView()).setText(nativeAd.getPrice());
}
if (nativeAd.getStore() == null) {
adView.getStoreView().setVisibility(View.INVISIBLE);
} else {
adView.getStoreView().setVisibility(View.VISIBLE);
((TextView) adView.getStoreView()).setText(nativeAd.getStore());
}
if (nativeAd.getStarRating() == null) {
adView.getStarRatingView().setVisibility(View.INVISIBLE);
} else {
((RatingBar) adView.getStarRatingView())
.setRating(nativeAd.getStarRating().floatValue());
adView.getStarRatingView().setVisibility(View.VISIBLE);
}
if (nativeAd.getAdvertiser() == null) {
adView.getAdvertiserView().setVisibility(View.INVISIBLE);
} else {
((TextView) adView.getAdvertiserView()).setText(nativeAd.getAdvertiser());
adView.getAdvertiserView().setVisibility(View.VISIBLE);
}
// This method tells the Google Mobile Ads SDK that you have finished populating your
// native ad view with this native ad. The SDK will populate the adView's MediaView
// with the media content from this native ad.
adView.setNativeAd(nativeAd);
// Get the video controller for the ad. One will always be provided, even if the ad doesn't
// have a video asset.
VideoController vc = nativeAd.getVideoController();
// Updates the UI to say whether or not this ad has a video asset.
if (vc.hasVideoContent()) {
videoStatus.setText(String.format(Locale.getDefault(),
"Video status: Ad contains a %.2f:1 video asset.",
vc.getAspectRatio()));
// Create a new VideoLifecycleCallbacks object and pass it to the VideoController. The
// VideoController will call methods on this object when events occur in the video
// lifecycle.
vc.setVideoLifecycleCallbacks(new VideoController.VideoLifecycleCallbacks() {
#Override
public void onVideoEnd() {
// Publishers should allow native ads to complete video playback before
// refreshing or replacing them with another ad in the same UI location.
refresh.setEnabled(true);
videoStatus.setText("Video status: Video playback has ended.");
super.onVideoEnd();
}
});
} else {
videoStatus.setText("Video status: Ad does not contain a video asset.");
refresh.setEnabled(true);
}
}
/**
* Creates a request for a new native ad based on the boolean parameters and calls the
* corresponding "populate" method when one is successfully returned.
*
*/
private void refreshAd() {
refresh.setEnabled(false);
builder = new AdLoader.Builder(this, ADMOB_AD_UNIT_ID);
builder.forUnifiedNativeAd(new UnifiedNativeAd.OnUnifiedNativeAdLoadedListener() {
// OnUnifiedNativeAdLoadedListener implementation.
#Override
public void onUnifiedNativeAdLoaded(UnifiedNativeAd unifiedNativeAd) {
// You must call destroy on old ads when you are done with them,
// otherwise you will have a memory leak.
if (nativeAd != null) {
nativeAd.destroy();
}
nativeAd = unifiedNativeAd;
FrameLayout frameLayout =
findViewById(R.id.fl_adplaceholder);
adView = (UnifiedNativeAdView) getLayoutInflater()
.inflate(R.layout.ad_unified, null);
populateUnifiedNativeAdView(unifiedNativeAd, adView);
frameLayout.removeAllViews();
frameLayout.addView(adView);
}
});
VideoOptions videoOptions = new VideoOptions.Builder()
.setStartMuted(startVideoAdsMuted.isChecked())
.build();
NativeAdOptions adOptions = new NativeAdOptions.Builder()
.setVideoOptions(videoOptions)
.build();
builder.withNativeAdOptions(adOptions);
AdLoader adLoader = builder.withAdListener(new AdListener() {
#Override
public void onAdFailedToLoad(int errorCode) {
refresh.setEnabled(true);
Toast.makeText(MainActivity.this, "Failed to load native ad: "
+ errorCode, Toast.LENGTH_SHORT).show();
}
}).build();
adLoader.loadAd(new AdRequest.Builder().build());
videoStatus.setText("");
}
Now I'm trying to put the code refresh method insaid dialog box instead of refresh method
public void showdilog(){
builder = new AdLoader.Builder(this, ADMOB_AD_UNIT_ID);
builder.forUnifiedNativeAd(new UnifiedNativeAd.OnUnifiedNativeAdLoadedListener() {
// OnUnifiedNativeAdLoadedListener implementation.
#Override
public void onUnifiedNativeAdLoaded(UnifiedNativeAd unifiedNativeAd) {
// You must call destroy on old ads when you are done with them,
// otherwise you will have a memory leak.
if (nativeAd != null) {
nativeAd.destroy();
}
nativeAd = unifiedNativeAd;
FrameLayout frameLayout =
findViewById(R.id.fl_adplaceholder);
adView = (UnifiedNativeAdView) getLayoutInflater()
.inflate(R.layout.ad_unified, null);
populateUnifiedNativeAdView(unifiedNativeAd, adView);
frameLayout.removeAllViews();
frameLayout.addView(adView);
}
});
VideoOptions videoOptions = new VideoOptions.Builder()
.setStartMuted(startVideoAdsMuted.isChecked())
.build();
NativeAdOptions adOptions = new NativeAdOptions.Builder()
.setVideoOptions(videoOptions)
.build();
builder.withNativeAdOptions(adOptions);
AdLoader adLoader = builder.withAdListener(new AdListener() {
#Override
public void onAdFailedToLoad(int errorCode) {
refresh.setEnabled(true);
Toast.makeText(MainActivity.this, "Failed to load native ad: "
+ errorCode, Toast.LENGTH_SHORT).show();
}
}).build();
adLoader.loadAd(new AdRequest.Builder().build());
AlertDialog.Builder builder = new AlertDialog.Builder(this);
bulider.setView(adView);
builder.setMessage(R.string.onfirm_exit)
.setCancelable(false)
.setPositiveButton(R.string.yes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
})
.setNegativeButton(R.string.no, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}

What you're doing is that you're building and showing your dialog box at the same time. So, at the time you show your dialog box you're also loading your native ad.
You should BUILD your dialog box in advance, and don't call alert.show() in your build function.
So, call your buildDialog() in MainActivity in advance.
In your onBackPressed function call alert.show().
Hope it helps.

How to retrieve a Boolean value from Firebase to a TextView?

I'm making a shopping app and User has to subscribe to the 'Fast-delivery' option if he needs to order it faster. When the User puts a tick to the 'Fast-delivery' Checkbox, the boolean value is being uploaded to the Firebase realtime database -->
database
And I want to see if the User has subscribed to the 'Fast-delivery' option from the Admin Panel. I retrieve all the order information to a RecyclerView in the Admin Panel. I want to set a TextView as "Fast Delivery : On/Off" when the Admin views the order details from the Admin Panel.
This is what I have tried:
#Override
protected void onStart()
{
super.onStart();
ordersRef = FirebaseDatabase.getInstance().getReference().child("Orders");
FirebaseRecyclerOptions<AdminOrders> options =
new FirebaseRecyclerOptions.Builder<AdminOrders>()
.setQuery(ordersRef, AdminOrders.class)
.build();
FirebaseRecyclerAdapter<AdminOrders, AdminOrdersViewHolder> adapter =
new FirebaseRecyclerAdapter<AdminOrders, AdminOrdersViewHolder>(options) {
#Override
protected void onBindViewHolder(#NonNull final AdminOrdersViewHolder holder, final int position, final #NonNull AdminOrders model)
{
holder.userName.setText("Name: "+ model.getName());
holder.userPhoneNumber.setText("Phone Number: : "+ model.getPhone());
holder.userTotalPrice.setText("Total Amount: $"+ model.getTotalAmount());
holder.userDateTime.setText("Order Time: "+ model.getDate() + model.getTime());
holder.userShippingAddress.setText("Shipping Address: "+ model.getAddress() + "," + model.getCity());
holder.showOrdersBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v)
{
String uID = getRef(position).getKey();
Intent intent = new Intent(AdminNewOrdersActivity.this, AdminUserProductsActivity.class);
intent.putExtra("uid", uID);
startActivity(intent);
}
});
ordersRef.child(userID).child("fast_delivery").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
TextView switch1 = (TextView) findViewById(R.id.switch1);
switch1.setText(String.valueOf(this));
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
And I'm getting this error
java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()

You have a NullPointerException indicating that userID is not initialized, hence this error:
Can't pass null for argument 'pathString' in child()
To solve this, please add the following line of code:
String userID = FirebaseAuth.getInstance().getCurrentUser().getUid();
Right in front of:
ordersRef.child(userID).child("fast_delivery").addValueEventListener(/* ... */);

i guess if im right.. you have created separate tree for orders where you are getting orders
create model class give name as same as childname are where you're getting boolean value of fast_delivery use that boolean value to convert it to string and hence compare that value if String.valueof(boolean)is="true" then print to textview or vise versa with off