I am trying to query Firebase and populate a recycler adapter with conditional data from the query's DataSnapshot. I tried putting the populate function inside the if statement that correctly logs the data I want, however the recycler view instead just returns everything from the node I was searching in (the main query I started with). Any suggestions on how to just populate the items that apply to the "if" statement? Thank you!
rootRef = FirebaseDatabase.getInstance().getReference();
//below is the node i query
mAlbumQuery = rootRef.child(Constants.FIREBASE_CHILD_ALBUMS).orderByChild("genres");
mAlbumQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot reco : dataSnapshot.getChildren()) {
if (reco.getValue().toString().contains(mRecommendation.getGenre())) {
//below returns the items i want
Log.d("is this correct", reco.getValue().toString());
//below returns everything in the original query
//how to populate only items that match the above?
mAdapter = new FirebaseRecyclerAdapter<Album, AlbumsViewHolder>(
Album.class,
R.layout.album_cards,
AlbumsViewHolder.class,
mAlbumQuery) {
#Override
public void populateViewHolder(AlbumsViewHolder holder, Album album, int position) {
holder.bindView(album.getImage(), album.getTitle());
if (!album.getGenres().contains(mRecommendation.getGenre())) {
//added as a hypothetical... should i have something in here?
}
}
};
mAlbumsRecycler.setAdapter(mAdapter);
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return view;
}
if you want to extract any particular node u can use this:-
String notific = String.valueOf(dataSnapshot.getValue());
int key=dataSnapshot.getKey();
String title=String.valueOf(dataSnapshot.child("title").getValue());
String content=String.valueOf(dataSnapshot.child("content").getValue());
Well, if you send mAlbumQuery as param to your FirebaseRecyclerAdapter, I believe, it takes its size as number of items.
As an option (for quick fix) you can create new collection and inside this loop:
for (DataSnapshot reco : dataSnapshot.getChildren()) {
}
you can fill that new collection with needed items.
After loop you can create new adapter and pass filtered collection to it.
Here is how I see this:
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Collection<> myNewCollection = new Collection<>(); //HashMap, ArrayList - depends on what you are storing in Firebase
for (DataSnapshot reco : dataSnapshot.getChildren()) {
if (reco.getValue().toString().contains(mRecommendation.getGenre())) {
//below returns the items i want
Log.d("is this correct", reco.getValue().toString());
//below returns everything in the original query
//how to populate only items that match the above?
myNewCollection.add(reco.getValue);
}
}
recyclerView.setAdapter(new MyRecyclerViewAdapter(myNewCollection, ...));
}
Also pls take a look at Firebase docs and this SO question.
There are interesting methods - startAt, endAt and equalTo, which might help you. I didn't find method contains, unfortunately, but methods above might be enough for you.
Related
I'm starting to code Android Apps with the database connection. As IDE I use Android Studio and Firebase for the database. This is my data structure in Firebase:
In my app, I need to fill a ListView with all the names. So I want the data from three children from the child "Rezepte" from the UUID child. I hope this is understandable.
I've done a lot of googling and I just can't figure out how this works. My current version of the java code is this:
final FirebaseUser user = firebaseAuth.getCurrentUser();
// trying to get the reference of the right path
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child(user.getUid()).child("Rezepte");
ref.addListenerForSingleValueEvent(
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// calling a method which should read the data from the snapshot and put it into the ListView
fillList((Map<String, Object>) dataSnapshot.child(user.getUid()).child("Rezepte").getValue());
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(RezepteActivity.this, "Daten konnten nicht gelesen werden", Toast.LENGTH_SHORT).show();
}
});
}
private void fillList(Map<String, Object> entries) {
// loop to cycle through every child of "Rezepte" and get the names
for (Map.Entry<String, Object> entry : entries.entrySet()) {
Map singleEntry = (Map) entry.getValue();
// add the name to an ArrayList of all names
Rezepte.add((String) singleEntry.get("name"));
}
// put the data into the ListView
lvRezepte.addFooterView(lvRezepte, Rezepte, true);
}
The app always crashes and I don't really understand a lot in the debugger. But the error occurs already in the onDataChange void.
I would be really happy if someone could help me.
You're trying to traverse down the hierarchy in your result DataSnapshot when you've already done so in your query itself. So in your onDataChange() you need to just put:
fillList(datasnapshot.getValue()) //Map of results at /{uid}/Rezepte
Assuming that fillList method works properly, you should first fix the following line
fillList((Map<String, Object>) dataSnapshot.child(user.getUid()).child("Rezepte").getValue())
to
fillList((Map<String, Object>) dataSnapshot.getValue())
You already have a reference to Rezepte child of the current user when you declared it like this:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child(user.getUid()).child("Rezepte")
Your snapshot has 1, 2, and 3 as children, so you shouldn't reinforce the path you declared in the reference.
To get all those names and add them to an ArrayList, please use the following code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference rezepeteRef = rootRef.child(user.getUid()).child("Rezepte");
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<String> list = new ArrayList<>();
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String name = ds.child("name").getValue(String.class);
list.add(name);
Log.d("TAG", name);
}
Log.d("TAG", list);
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
rezepeteRef.addListenerForSingleValueEvent(eventListener);
my data look like this
and I simply want to add an object at index 3. How could I add it there. Is there any way to add an object without iteration or I have to iterate and getChildCount and then append new child("3") and it's data to it.
TransGenderBO transGenderBO = new TransGenderBO();
transGenderBO.setName("pushName");
transGenderBO.setAge(13);
mRef.child("").setValue(transGenderBO);
there is no method in mRef for getting child count and appending new item at 3 position..
Edit after using Frank code but still not working
Query last = mRef.orderByKey().limitToLast(1);
last.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
int lastIndex = 0;
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
lastIndex = Integer.parseInt(childSnapshot.getKey());
}
TransGenderBO transGenderBO = new TransGenderBO();
transGenderBO.setName("pushName");
transGenderBO.setAge(13);
mRef.child(""+(lastIndex+1)).setValue(transGenderBO);
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(mContext,databaseError.getMessage(),Toast.LENGTH_LONG).show();
}
});
There is a good reason that the Firebase documentation and blog recommend against using arrays in the database: they don't work very well for multi-user applications where users can be offline.
To add the next element to your array here, you'll have to download at the very least the last element of the array to know the index of the next element:
Query last = root.orderByKey().limitToLast(1);
last.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
int lastIndex;
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
lastIndex = Integer.parseInt(childSnapshot.getKey());
}
root.child(""+(lastIndex+1)).setValue(true);
}
But this has an inherent race-condition. When multiple users are adding elements to the array at the same time, they may end up writing to the same index.
To prevent this you can use a Firebase transaction. With this you get the current value from a location and in exchange return the new value you want at that location. This ensures that no data is overwritten between users, but means that you have to download the entire array.
And neither of these scenarios works when a user is not connected to the network.
Firebase instead recommends using so-called push IDs, which:
Generate a always-increasing key that is guaranteed to be unique.
Do not require reading any data - they are generated client-side and are statistically guaranteed to be unique.
Also work when a user is offline.
The only disadvantage is that they're not as easily readable as array indexes.
Get your data like this
private ArrayList<TransGenderBO> transGenderBO;
FirebaseDatabase.getInstance().getReference().child("Main")
.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
transGenderBO = (ArrayList<TransGenderBO>) dataSnapshot.getValue();
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
and set your value like this
TransGenderBO transGender = new TransGenderBO();
transGender.setName("pushName");
transGender.setAge(13);
FirebaseDatabase.getInstance().getReference().child("Main").child(String.valueOf(transGenderBO.size())).setValue(transGender);
or U can set this way too
TransGenderBO transGender = new TransGenderBO();
transGender.setName("pushName");
transGender.setAge(13);
TransGenderBO.add(transGender);
FirebaseDatabase.getInstance().getReference().child("Main")
.setValue(transGenderBO);
I have this scenario where in my app i am trying to query the child nodes and pass it on the list to recyclerview adapter and here comes the problem when i am scrolling up the recycler view items and if some one has inserted a post, my recyclerview is again coming to first post item and also i am using the viewpager with three fragments and whatever fragment i am on I am rolling back to the first fragment if some one has inserted the post how to solve this.
I have implemented this in following way mentioned below.
one way im thinking is i thought i would not listen to the childevent changes instead i would query the results and populate recyclerview later not listening to child events so that way everything states as it is and i dont know in firebase how do you retrieve values without implementing listeners I tried the singleValueEventListener that way still the behavior is same rolling back to first item or first fragment
guide me through solution how to get rid of this behavior.
Query query= databasePostsReference.orderByChild("timestamp");
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<UserPostPOJO> listposts = new ArrayList<UserPostPOJO>();
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
Log.d(TAG, "onDataChange: entered list adding");
UserPostPOJO post =
snapshot.getValue(UserPostPOJO.class);
listposts.add(0,post);
}
if(listposts.isEmpty()){
empty.setVisibility(View.VISIBLE);
recyclerView.setVisibility(View.GONE);
}
else
{
empty.setVisibility(View.GONE);
recyclerView.setVisibility(View.VISIBLE);
makelist(listposts);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
private void makelist(List<UserPostPOJO> listposts) {
list = listposts;
Log.d(TAG,"size is "+ list.size()+"");
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new
LinearLayoutManager(getActivity()));
CustomRecyclerViewAdapter adapter = new
CustomRecyclerViewAdapter(getActivity(), list,"recentfragment");
recyclerView.setAdapter(adapter);
}
There is a method called removeEventListener() that you can call to remove a specific event listener. You get data out from your database and than call this method. So in order to make this work, please use the following code:
databaseReference.removeEventListener(valueEventListener);
In which databaseReference is the reference where you intially put the listener.
For more details please read the offcial doc.
Hope it helps.
Firebase has a FirebaseRecyclerAdapter which can be set to a RecyclerView. It takes a DatabaseReference or Query object and handles all the data synchronization between your database and your view.
For a database reference object, the same way one can add an event listener, it can also be removed, using removeEventListener.
Instead of creating an anonymous object like this
Query query= databasePostsReference.orderByChild("timestamp");
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<UserPostPOJO> listposts = new ArrayList<UserPostPOJO>();
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
Log.d(TAG, "onDataChange: entered list adding");
UserPostPOJO post =
snapshot.getValue(UserPostPOJO.class);
listposts.add(0,post);
}
if(listposts.isEmpty()){
empty.setVisibility(View.VISIBLE);
recyclerView.setVisibility(View.GONE);
}
else
{
empty.setVisibility(View.GONE);
recyclerView.setVisibility(View.VISIBLE);
makelist(listposts);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
you can create a named object of ValueEventListener and remove it from the database reference object using removeEventListener, at the end of the onDataChange method
Query query= databasePostsReference.orderByChild("timestamp");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<UserPostPOJO> listposts = new ArrayList<UserPostPOJO>();
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
Log.d(TAG, "onDataChange: entered list adding");
UserPostPOJO post =
snapshot.getValue(UserPostPOJO.class);
listposts.add(0,post);
}
if(listposts.isEmpty()){
empty.setVisibility(View.VISIBLE);
recyclerView.setVisibility(View.GONE);
}
else
{
empty.setVisibility(View.GONE);
recyclerView.setVisibility(View.VISIBLE);
makelist(listposts);
}
query.removeEventListener(valueEventListener);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
query.addValueEventListener(valueEventListener);
The code inside onDataChange method gets executed only once as the ValueEventListener object is removed as soon as the last line of the method gets executed.
I'm new to Firebase and NoSQL. I have an Android Demo, with a City Autocomplete Text Field in which I want to populate the cities I have from my Firebase DB, while typing.
{ "cities":{
"Guayaquil":true,
"Gualaceo":true,
"Quito":true,
"Quevedo":true,
"Cuenca":true,
"Loja":true,
"Ibarra":true,
"Manta":true
}
}
This is what I have so far.
How can I retrieve from the DB cities that start with a letter (input from keyboard)? If I start typing "G", I want to receive "Guayaquil" and "Gualaceo".
If I use orderByValue always returns an empty snapshot.
If I use orderByKey return the whole list.
Query citiesQuery = databaseRef.child("cities").startAt(input).orderByValue();
citiesQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<String> cities = new ArrayList<String>();
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
cities.add(postSnapshot.getValue().toString());
}
Note: If you can recommend a better data structure, you're welcome.
#NicholasChen has identified the problem. But here's the way you'd implement using the 3.x SDK:
DatabaseReference cities = databaseRef.child("cities")
Query citiesQuery = cities.orderByKey().startAt(input).endAt(input+"\uf8ff");
citiesQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<String> cities = new ArrayList<String>();
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
cities.add(postSnapshot.getValue().toString());
}
By starting at the user input and ending at the last string that starts with the user input, you get all matching items
For relatively short lists of items Ryan's approach will also work fine. But the above Firebase query will filter server-side.
Update
I just ran this code:
DatabaseReference databaseRef = FirebaseDatabase.getInstance().getReference("39714936");
String input = "G";
DatabaseReference cities = databaseRef.child("cities");
Query citiesQuery = cities.orderByKey().startAt(input).endAt(input + "\uf8ff");
citiesQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List<String> cities = new ArrayList<String>();
for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
cities.add(postSnapshot.getValue().toString());
}
System.out.println(cities);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
And it printed:
true
true
So clearly matches two cities.
Feel free to test against my database: https://stackoverflow.firebaseio.com/39714936
Try something like this to iterate over the children in the cities snapshot and add all the cities to an ArrayList of Strings.
ArrayList<String> cityList = new ArrayList<>();
databaseRef.child("cities").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
cityList.clear();
for (DataSnapshot data : dataSnapshot.getChildren()){
cityList.add(data.getKey);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Log.w(TAG, "getUser:onCancelled", databaseError.toException());
// ...
}
});
Editing this paragraph for clarity:
This will get all your cities read into the program memory so you can use that data to display the cities to the user. If the city list changes, so will the data the user sees. If the user is not online, this will not work. This puts a real time, online only listener on the database.
The logic in my mind is something like:
Set a value listener on the text box.
When user types, make a view display all the items in the array list
that start with the same substring that was typed.
Handle arrayIndex errors of course.
Hopefully this will get you on the right track. I am sure there are other ways you could implement it but this is what I would personally do. If you need help with the code to display the correct cities, start a chat with me and I can brainstorm with you.
Of course OrderByValue returns nothing because that's the booleans you have.
you can use the startAt and endAt methods to do so. (The below is Firebase 2.0's Code)
var ref = new Firebase("https://dinosaur-facts.firebaseio.com/dinosaurs");
ref.orderByKey().startAt("b").endAt("b\uf8ff").on("child_added", function(snapshot) {
console.log(snapshot.key());
});
You can explore more on the Firebase 3 documentation site here.
What Ryan did was right. However, you have to implement startAt on the dataSnapshot to make sure that your "live" search works.
I am new to firebase and android.
I am populating a listview with data from firebase using firebase List adapter.
I understand that we can not chain filters in firebase.
Below is the code snippet from the activity. I created a firebase reference. Then I applied the equalTo filter to get items with category=clothes.
Query orderedActiveUserListsRef;
Firebase activeListsRef = new Firebase(Constants.FIREBASE_URL_USER_LISTS)
.child(mEncodedEmail);
orderedActiveUserListsRef = activeListsRef.orderByChild("category").equalTo("clothes");
I would like to further filter out results from orderedActiveUserListsRef before supplying it to the adapter.
One approach I found is creating an array by iterating the orderedActiveUserListsRef using the below code:
orderedActiveUserListsRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot messageSnapshot: dataSnapshot.getChildren()) {
String category = (String) messageSnapshot.child("category").getValue();
Log.d("CatList",category);
}
}
#Override
public void onCancelled(FirebaseError firebaseError) { }
});
Please advise the best possible approach.
PS: I have denormalised the data.