I am retrieving data from Firebase and use this data to present some information. Since retrieving data takes time I put a CountDownTimer to make the app wait but it is not a nice solution and it does not look good. I found that Android Loader can do this job but I could not make it work. Can anyone solve this?
Here is the code I use to get data from Firebase.
infoReference.addChildEventListener(new ChildEventListener() { //inforeference is DatabaseReference
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
try {
Info info = postSnapshot.getValue(Info.class);
infoList.add(info); //Just an arraylist
}catch(Exception e){
}
}
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
I use
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
doSomething();
}
},2000);
right after retrieving data from firebase,yet not a very good idea. looking for solution too.
Related
This question already has an answer here:
ArrayList not updating inside onChildAdded function
(1 answer)
Closed 4 years ago.
I want to get the whole value(0~5) from destinations
This is part of json data in realtime database
{"results" : [{
"destin_num" : 6,
"destinations" : [ "asdf", "qwwee", "zzzxcv11", "jkkk", "lkjhhg", "zxcvb" ],
"name" : "asdfasdfff",
"order" : 2,
"required_time" : "6hours" }]}
the value I want to put in the String List , I use ChildEventListener() to add the value into List, but the value can't put into the List after finish the ChildEventListener().There will be nothing in List direction How to get the values?
List<String> direction=new ArrayList<String>();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
DatabaseReference reference_contacts = FirebaseDatabase.getInstance().getReference("results").child("1").child("destinations");
reference_contacts.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
String data=dataSnapshot.getValue().toString();
direction.add(data);
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
for(int i=0;i<direction.size();i++){
Log.e("Get data",direction.get(i));
}
}
It's because data is loaded from Firebase asynchronously. Your for loop printing the values is actually run before onChildAdded ever gets called. It's easiest to see this by adding some logging:
Log.i("Firebase", "Before adding listener");
reference_contacts.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
Log.i("Firebase", "In onChildAdded");
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) { }
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) { }
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) { }
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
Log.i("Firebase", "After adding listener");
When you run this code it prints:
Before adding listener
After adding listener
In onChildAdded
That is probably not the order you expected. But is completely explains why the direction list is empty when you print it, the data hasn't been loaded yet, so onChildAdded has never been invoked.
The solution is typically to add the code that requires the data into the onChildAdded method:
So:
reference_contacts.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
String data=dataSnapshot.getValue().toString();
direction.add(data);
Log.i("Got data",direction);
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
If you only want to show the data once everything is loaded, you can use a ValueEventListener instead:
reference_contacts.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
for (DataSnapshot dataSnapshot: snapshot.getChildren()) {
String data=dataSnapshot.getValue(String.class);
direction.add(data);
}
for(int i=0;i<direction.size();i++){
Log.e("Get data",direction.get(i));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
Note that this is an incredibly common source of confusion for developers new to Firebase (and asynchronous APIs in general). I highly recommend studying some of the answers to some of these previous questions about the topic:
Setting Singleton property value in Firebase Listener
getContactsFromFirebase() method return an empty list (which also shows how to define a custom interface to allow the code that requires the data to be outside onChildAdded/onDataChange.
can't get values out of ondatachange method
ArrayList not updating inside onChildAdded function
I am facing a problem with adding older data to RecyclerView with SwipeRefreshLayout so, here is how i retrieve from Firebase and put data into RecyclerView
private void messageList() {
referenceMessages.orderByKey().limitToLast(10).addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
MessagesInfo messages = dataSnapshot.getValue(MessagesInfo.class);
result.add(messages);
adapter.notifyDataSetChanged();
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
MessagesInfo messages = dataSnapshot.getValue(MessagesInfo.class);
result.remove(messages);
adapter.notifyDataSetChanged();
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
as you can i see, I set limit of retrieved messages to last 10, what means the 10 newest messages will be displayed. So far everything works great, the messages are displayed like that
-20thmessage(the oldest)-
-21stmessage-
-...-
-29thmessage-
-30thmessage(the newest)-
now i use SwipeRefreshLayout like that
private void swipe(){
swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
#Override
public void onRefresh() {
referenceMessages.orderByKey().endAt("-LHUhkub4iaZNNzmtUcs").limitToLast(10).addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
MessagesInfo messages = dataSnapshot.getValue(MessagesInfo.class);
recyclerView.scrollToPosition(0);
result.add(0, messages);
adapter.notifyDataSetChanged();
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});
}
and it retrieves data properly, i mean previous 10 messages before hardcoded endAt() but after swiping places data not properly. If i dont use index 0
new data is placed at the botoom of latest message and it looks like that
-30thmessage(the newest)-
-10thmessage-
-...-
-19thmessage-
-20thmessage(the newest)-
and when i use index 0 data is added from the top of already loaded messages but like that
-20thmessage(the oldest)-
-19thmessage-
-...-
-11ththmessage-
-10th-
so it is added upside-down. Hope you understand me :) any inputs are highly appreciated
You might try clearing the list first and then add the new messages.
Android SwipeRefreshLayoutBasic
public void readUniversity(){
ChildEventListener uniListener = new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
//Log.d(LOG_TAG, dataSnapshot.getKey());
University uni = dataSnapshot.getValue(University.class);
universitieslist.add(uni); //Adding to an ArrayList of type University
//Log.d(LOG_TAG, universitieslist.size()+"is the size");
arrayofUniversities.add(uni.getName()); //Adding name of University to list
//Log.d(LOG_TAG, adapter.getCount() + " items");
//Log.d(LOG_TAG, arrayofUniversities.size()+" is the size");
adapter.notifyDataSetChanged();
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
};
DatabaseReference uniReference = database.getReference("note-retrieve/Universities");
uniReference.addChildEventListener(uniListener);
}
The code is pretty much self explanatory. I am using arrayofUniversities a list to populate a spinner so I need an adapter. I am populating the spinner with the names of the Universities
I am storing the University Objects in universitieslist
The problem I have is when I leave the readUniversity() method I lose every element in universitieslist and arrayofUniversities even though my spinner is populated with these.
Its very strange as the list should have the objects stored.
Also, I have my adapter at the very top of the code in onCreate().
Try this way. Hope it will work .. :)
private Arrylist<University > universityList = new ArryList<>();
private Arrylist<String> universitysName = new ArryList<>();
mDatabase.getReference().child("path")
.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot != null) {
University mUniversity = dataSnapshot.getValue(University
.class);
universityList.add(mUniversity);
universitysName.add(mUniversity.getName);
}
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
The problem seems to be with the adapter, if you can see the logs but the adapter is not updating, then is because the adapter is not being notified the data set has changed
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot != null) {
University mUniversity = dataSnapshot.getValue(University
.class);
universityList.add(mUniversity);
universitysName.add(mUniversity.getName);
//UPDATE YOUR ADAPTER HERE
//spinnerAdapter.notifyDataSetChanged();
}
}
But I think the real problem is the origin of your current problem: You are getting each child. This is a way to do it, but for this case where you need all the data first and when that is ready show the spinner with the elements to the user, you should better get all the list elements in one query.
database.getReference("note-retrieve/Universities")..addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
University mUniversity = dataSnapshot.getValue(University
.class);
universityList.add(mUniversity);
universitysName.add(mUniversity.getName);
//ONCE THIS IS DONE, THEN PASS THE ARRAY TO THE ADAPTER
}
//The loop here is over, so you can set the adapter with the full list of data/universities
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
My structure is like following
- Posts
- keu23jndf
- dateTime:"2376464"
- name:"abc"
- key34njf
- dateTime:"4333434"
- name:"xyz"
Now, I want to retrieve sorted data by dateTime in descending order.
Thanks
Ok so first of all I would suggest you to not use a client sided timestamp but instead use the ServerValue.TIMESTAMP. In most cases this is going to be the better setup. If you know what you are doing and you want it exactly like that, forget this and just read on.
The problem if you want to sort from newest to oldest is that Firebase does (as far as I know) not support this.
A workaround would be to use the negative value of the Firebase ServerValue.TIMESTAMP.
This is how I do it. It may not be the perfect or right way, but it does work
private void prepareUpload() {
//mDatabase is a reference to the root of the Firebase Database
final DatabaseReference timestampReference = mDatabase.child("timestamp");
final String timestampKey = timestampReference.push().getKey();
timestampReference.child(timestampKey).setValue(ServerValue.TIMESTAMP);
timestampReference.child(timestampKey).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.getValue() != null) {
Long timestamp = 0 - Long.parseLong(dataSnapshot.getValue().toString());
upload(/*Starting upload with new timestamp here (this is just a dummy method)*/);
timestampReference.child(timestampKey).removeValue();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Log.e(TAG, databaseError.getMessage());
}
});
}
Now you have to set your Firebase Database rules as follows:
"Posts": {
".indexOn" : "date",
...
}
Finally you just have to query your 'Posts' somehow like this:
mDatabase.child("Posts").orderByChild("dateTime").addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
//Do stuff with your data
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Hope this helps!
I'm fetching some strings in firebase which are all saved under tag 'imageUID' and using this imageUIDs to show images.
Here's how I'm fetching it:
databaseReference.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
Map<String, String> newRequest = (Map<String, String>) dataSnapshot.getValue();
imageUID = newRequest.get("imageUID");
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
This is how I'm using the above fetched imageUID to show images:
private void doSomethingWithPicasso(String imageUIDh, ImageView target){
Picasso.with(getBaseContext())
.load(imageUIDh)
.error(R.drawable.ic_warning_black_24dp)
.into(target, new Callback() {
#Override
public void onSuccess() {
progressBar.setVisibility(View.INVISIBLE);
}
#Override
public void onError() {
Toast.makeText(getBaseContext(), "Error occurred while loading images. Please retry.", Toast.LENGTH_SHORT).show();
}
});
}
I want to show each every image shown using imagesUIDs fetched from database in my app, but what is happening is only the last imageUID is getting used to show images and not all of them.
I was thinking about looping through this string and using each string one by one to show images, but I don't know how to do that! Is there any better way to achieve this?
you may get some help from this try this
firebase.child("key").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot innerDataSanpShot : dataSnapshot.getChildren()) {
//DataSnapshot of inner Childerns
String username = innerDataSnapShot.child("username").getValue().toString();
}
}
#Override
public void onCancelled(FirebaseError firebaseError) {
}
});