As we know there is no multi query option to firebase realtime database, so instead of using default FirebaseRecycler methods I am trying to manually feed keys from arraylist to the recycler view. In order to sort specific keys on the basis specific child nodes of the given parent I wrote below logic.
If I try to individually log the keys in if statement it shows displays all the sorted keys.
But now my problem is whenever I try to log the arraylist after fetching the values it shows null and if I log specific value at some index below error shows up.
public class categorizedProducts extends AppCompatActivity {
private String catKey;
private DatabaseReference productRef, catRef;
private ArrayList<String> keyVal = new ArrayList<>();
private long count = 0;
private long i = 0;
private void queryLogic(final String catTitle) {
productRef.orderByChild("count").addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
count = dataSnapshot.getChildrenCount();
for (final DataSnapshot snap: dataSnapshot.getChildren()){
productRef.child(Objects.requireNonNull(snap.getKey())).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
if (Objects.requireNonNull(dataSnapshot.child("category").getValue()).toString().equals(catTitle)) {
//keyVals.add(snap.getKey());
keyVal.add(snap.getKey());
i++;
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
// I am trying to log my arraylist here after retrieving the required keys from database
}
2020-06-27 19:50:32.315 567-567/com.kalpana.mortoys E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kalpana.mortoys, PID: 567
java.lang.IndexOutOfBoundsException: Index: 1, Size: 0
at java.util.ArrayList.get(ArrayList.java:437)
at com.kalpana.mortoys.categorizedProducts$1.onDataChange(categorizedProducts.java:65)
at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.1:75)
at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.1:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.1:55)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7397)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:935)
I temporarily solved my error using this
public class categorizedProducts extends AppCompatActivity {
private String catKey;
private DatabaseReference productRef, catRef;
private ArrayList<String> keyVal = new ArrayList<>();
private long count = 0, i = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_categorized_products);
initFields();
try {
Bundle bundle = getIntent().getExtras();
assert bundle != null;
catKey = bundle.getString("key");
assert catKey != null;
catRef.child(catKey).addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
queryLogic(Objects.requireNonNull(dataSnapshot.child("catTitle").getValue()).toString());
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
catch (NullPointerException e) {
e.printStackTrace();
}
}
private void initFields() {
productRef = FirebaseDatabase.getInstance().getReference().child("products");
catRef = FirebaseDatabase.getInstance().getReference().child("categories");
}
@Override
protected void onStart() {
super.onStart();
if (i == count) {
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Log.i("TAG", "onStart: " + keyVal);
}
}, 3000);
}
}
private void queryLogic(final String catTitle) {
productRef.orderByChild("count").addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
count = dataSnapshot.getChildrenCount();
for (final DataSnapshot snap: dataSnapshot.getChildren()){
i++;
productRef.child(Objects.requireNonNull(snap.getKey())).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
if (Objects.requireNonNull(dataSnapshot.child("category").getValue()).toString().equals(catTitle)) {
//keyVals.add(snap.getKey());
keyVal.add(snap.getKey());
//Log.i("TAG", "onDataChange: " + i);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
but still need an perfect solution
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Answer
You could use a callback interface:
interface CallBack {public void done()}
and call queryLogic() as
queryLogic(catTitle,new CallBack() {
public void done() {
//log your arrayList here
}
});
private void queryLogic (final String catTitle,final CallBack callBack){..}
and after the iteration is over just call the method callBack.done().