Develop Reference

How to populate an ArrayAdapter with a List of objects from a Firebase Database?

I'm trying to populate my ListView with User objects from Firebase Database. I've seen some people use RecyclerView but I cannot get RecyclerView to work on my Android Studio (maybe i'm using incompatible dependencies).
Anyway here is my code:
// necessary imports
public class List extends AppCompatActivity {
ListView usersList;
private DatabaseReference userDatabase;
ArrayList<String> list = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
usersList = (ListView) findViewById(R.id.list_users);
userDatabase = FirebaseDatabase.getInstance().getReference().child("Users");
}
#Override
protected void onStart() {
super.onStart();
// Populate ArrayAdapter with User objects from Firebase Database.
ArrayAdapter<Users> Adapter = new ArrayAdapter<Users>(this, Users.class, android.R.layout.simple_expandable_list_item_1, userDatabase){
// Populate here, don't know what to do.
};
usersList.setAdapter(Adapter);
usersList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Users.connectTo = list.get(i);
Intent chatActivity = new Intent(List.this, ChatActivity.class);
startActivity(chatActivity);
}
});
}
}
I know my ArrayList takes a String at the beginning, I will change that to Users.
ArrayAdapter parameters are not working, despite looking at the docs and it telling me this way.
Not sure how to properly implement RecyclerView
Not got much experience with Android Studio/Java.

List from map wont appear in my ListView

I made a list of values from a map retrieved from firestore database. The problem is that it won't appear on my listView. I initiated another list from another map and it appeared in my listView. Why is the list from the map retrieved from firestore document won't work while other list works fine?
public class RecipeActivity extends Activity {
private ListView listView;
private ArrayAdapter<Object> arrayAdapter;
private FirebaseFirestore newRecipeDb;
private Map<String, Object> meMap = new HashMap<String, Object>();
private List<Object> list = new ArrayList<>();
private List<String> listStrings = new ArrayList<> ();
private TextView textView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recipe);
textView = findViewById(R.id. breadRecipe);
listView = findViewById(R.id.listIngredient);
arrayAdapter = new ArrayAdapter<Object>(this,
android.R.layout.simple_list_item_activated_1, list);
newRecipeDb = FirebaseFirestore.getInstance();
newRecipeDb.collection("users")
.document("bakeryMgt")
.collection("New Recipe")
.document("cherri pie")
.get()
.addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document.exists()) {
System.out.println("DocumentSnapshot data " + document.getData());
meMap = document.getData();
list = new ArrayList<Object>(meMap.values());
listView.setAdapter(arrayAdapter);
} else {
System.out.println("No such document");
}
} else {
System.out.println("get failed with " + task.getException());
}
}
});
}
}

In your onCreate you're creating an ArrayAdapter based on list:
arrayAdapter = new ArrayAdapter<Object>(this,
android.R.layout.simple_list_item_activated_1, list);
Then inside onComplete, you create a new list:
list = new ArrayList<Object>(meMap.values());
This means that the arrayAdapter is not pointing to the list that you put the data into.
The solution is to add the data from the document to the existing list:
list.add(meMap.values());
I'd also recommend tying the adapter to the list view when you initialize both:
listView = findViewById(R.id.listIngredient);
arrayAdapter = new ArrayAdapter<Object>(this,
android.R.layout.simple_list_item_activated_1, list);
listView.setAdapter(arrayAdapter);
And then only notify the adapter that its data changed, once you add an item to the list:
list.add(meMap.values());
arrayAdapter.notifyDataSetChanged();

RecyclerView: No adapter attached - why do I keep getting this error?

Just trying to show in a RecyclerView the info from my database.
everything works fine. The objects are displayed.
but logcat says:
E/RecyclerView: No adapter attached; skipping layout
This is my the code (DisplayImages.java)
public class DisplayImages extends AppCompatActivity {
DatabaseReference databaseReference;
RecyclerView recyclerView;
RecyclerView.Adapter adapter;
ProgressDialog progressDialog;
List<ImageUploadInfo> list = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_display_images);
recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(DisplayImages.this));
progressDialog = new ProgressDialog(DisplayImages.this);
progressDialog.setMessage("Loading Images From Firebase.");
progressDialog.show();
// Setting up Firebase image upload folder path in databaseReference.
// The path is already defined in MainActivity.
databaseReference = FirebaseDatabase.getInstance().getReference(Main.Database_Path);
databaseReference.addValueEventListener(new ValueEventListener() {
#override
public void onDataChange(DataSnapshot snapshot) {
for (DataSnapshot postSnapshot : snapshot.getChildren()) {
ImageUploadInfo imageUploadInfo = postSnapshot.getValue(ImageUploadInfo.class);
list.add(imageUploadInfo);
}
adapter = new RecyclerViewAdapter(getApplicationContext(), list);
recyclerView.setAdapter(adapter);
progressDialog.dismiss();
}
#Override
public void onCancelled(DatabaseError databaseError) {
progressDialog.dismiss();
}
});
}
And If it makes any difference, this is what i wrote in MainActivity about the DataBase_Path :
public class Main extends AppCompatActivity implements View.OnClickListener {
DatabaseReference databaseReference;
public static final String Database_Path = "All_Image_Uploads_Database";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
databaseReference = FirebaseDatabase.getInstance().getReference(Database_Path);
As you can see I have attached an adapter for Recycleview. so why do I keep getting this error?
i have read other questions related to same problem but none helps.

Yyou need to set the adapter after you set the layour manager, otherwise you'll get the error message you're seeing.
recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
recyclerView.setHasFixedSize(true);
//don't set adapter here
recyclerView.setLayoutManager(new LinearLayoutManager(DisplayImages.this));
//set adapter here
Moreover, you can set the adapter with an empty list first and then when you receive the callback from firebase you can update the list and call notifyDatasetChanged() on the adapter. The problem you see is due to the fact that you're not actually setting the adapter until very later in the process (when your firebase call comes back)
Like this:
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(DisplayImages.this));
adapter = new RecyclerViewAdapter(getApplicationContext(), list);
recyclerView.setAdapter(adapter);
databaseReference.addValueEventListener(new ValueEventListener() {
#override
public void onDataChange(DataSnapshot snapshot) {
for (DataSnapshot postSnapshot : snapshot.getChildren()) {
ImageUploadInfo imageUploadInfo = postSnapshot.getValue(ImageUploadInfo.class);
list.add(imageUploadInfo);
}
adapter.notifyDatasetChanged();
}
#Override
public void onCancelled(DatabaseError databaseError) {
progressDialog.dismiss();
}
});

I don't see anywhere you are creating an adapter and setting that adapter to RecyclerView. You need to create an adapter and set adapter like following:
mAppAdapter = new AppAdapter(mModel); // or whatever constructor you want
recyclerView.setAdapter(mAppAdapter);
EDIT:
You are setting adapter to RecyclerView inside an asynchronous method. So your program will have a non deterministinc amount of time where the adapter is not actually set to recyclerView. To get rid off the warning you get you should initialize and set the adapter above the async method and only update data of the adapter inside the async method

Listview not displaying response from retrofit api call

I made a retrofit call in android and got a list response objects back but for some reason, they are not getting displayed in the listview and the application is not crashing either.
public class MainActivity extends AppCompatActivity {
private OpenNotifyService mService;
ListView listView ;
List<Response> arrayList = new ArrayList<Response>();
ArrayAdapter<Response> adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mService = ApiUtils.getOpenNotifyService();
// Get ListView object from xml
listView = findViewById(R.id.myListView);
adapter = new ArrayAdapter<Response>(this,android.R.layout.simple_list_item_1, android.R.id.text1, arrayList);
loadAnswers();
}
public void loadAnswers() {
mService.getTimes(12,10).enqueue(new Callback<InternationalSpaceStationPassTimes>() {
#Override
public void onResponse(Call<InternationalSpaceStationPassTimes> call, retrofit2.Response<InternationalSpaceStationPassTimes> response) {
Log.e("Request URL", call.request().url().toString());
if (response.isSuccessful()) {
arrayList= response.body().getResponse();
// Assign adapter to ListView
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
int itemPosition = position;
// ListView Clicked item value
String itemValue = (String) listView.getItemAtPosition(position);
// Show Alert
Toast.makeText(getApplicationContext(),
"Position :"+itemPosition+" ListItem : " +itemValue , Toast.LENGTH_LONG)
.show();
}
});
Log.d("MainActivity", "posts loaded from API");
} else {
int statusCode = response.code();
// handle request errors depending on status code
}
}
#Override
public void onFailure(Call<InternationalSpaceStationPassTimes> call, Throwable t) {
Log.d("MainActivity", "error loading from API");
}
});
}
Please help me..

Your list is initialized when your Activity instance is constructed:
List<Response> arrayList = new ArrayList<Response>();
During onCreate(), your adapter is constructed:
adapter = new ArrayAdapter<Response>(this,
android.R.layout.simple_list_item_1,
android.R.id.text1,
arrayList);
Inside your loadAnswers() callback, your list is reinitialized:
arrayList= response.body().getResponse();
Finally, you attach the adapter to the listview:
listView.setAdapter(adapter);
Your problem is that your callback assigns a different List instance to your arrayList variable. Since your adapter was already created at this point, this means that the list inside of adapter is different from the list pointed to by arrayList. So nothing will appear.
You can solve this a couple of different ways. Probably the easiest would be to change your loadAnswers() callback to do this instead:
arrayList.clear();
arrayList.addAll(response.body().getResponse());
adapter.notifyDataSetChanged();

Firebase data retrieval returns an empty screen

I am trying to retrieve data from firebase to a listview...However this code returns a blank screen .My database has got 3 children with for data fields each.
All i see is an empty screen.
I have no idea on how to solve this anyone please:The code is here
public class Business extends AppCompatActivity {
private ListView business;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_business);
}
public ArrayList<String> arr;
public ArrayAdapter adapter;
#Override
protected void onStart() {
super.onStart();
DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
arr = new ArrayList<>();
ValueEventListener listener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
map2list((Map) dataSnapshot.getValue());
//formats the datasnapshot entries to strings
adapter.notifyDataSetChanged();
//makes the ListView realtime
}
#Override
public void onCancelled(FirebaseError firebaseError) {
}
public void onCancelled(DatabaseError databaseError) {
// Getting Post failed, log a message
System.out.println(databaseError.toException());
// ...
}
};
mDatabase.addValueEventListener((com.google.firebase.database.ValueEventListener) listener);
adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, arr);
ListView listView = (ListView) findViewById(R.id.business);
listView.setAdapter(adapter);
}
public void map2list(Map<String,Long> map){
arr.clear();
for (Map.Entry<String, Long> entry : map.entrySet()) {
Long key = Long.parseLong(entry.getKey());
String d = DateFormat.getDateTimeInstance().format(key);
Long value = entry.getValue();
arr.add(d + ": " + value);
}
}
}

If the whole page is blank when you set the content view, this might have happened if one of your views in your layout has a layout_height attribute of 'match parent'. This may be one of the reasons why you are not seeing anything. Another reason why you might not bee seeing anything is that listeners run on separate threads. Try rearranging your code like this.
adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, arr);
ListView listView = (ListView) findViewById(R.id.business);
listView.setAdapter(adapter);
mDatabase.addValueEventListener((com.google.firebase.database.ValueEventListener) listener);
// add the listner after setting the adapter