Develop Reference

Increment values in firebase realtime

There can be mutiple people on the app click a button that will Increment value in firebase and get that value back, but if each person clicks the button at the same time right now, they will get the same value, how do I Increment with each person getting a differnt value?
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("queue");
reference.child(queue_id).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
currentNum = (long) dataSnapshot.child("currentNumber").getValue();
++currentNum;
dataSnapshot.child("currentNumber").getRef().setValue(++currentNum);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

To prevent conflicts from multiple users updating the same node at (almost) the same time, you need to use a transaction. In your case that'd look something like:
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("queue");
DatabaseReference numberRef = reference.child(queue_id).child("currentNumber");
numberRef.runTransaction(new Transaction.Handler() {
#Override
public Transaction.Result doTransaction(MutableData mutableData) {
Long value = mutableData.getValue(Long.class);
if (value == null) {
mutableData.setValue(1);
}
else {
mutableData.setValue(value+1);
}
return Transaction.success(mutableData);
}
}
#Override
public void onComplete(DatabaseError databaseError, boolean b,
DataSnapshot dataSnapshot) {
// Transaction completed
Log.d(TAG, "runTransaction:onComplete:" + databaseError);
}

As per your code, you're incrementing the counter by 1 but you are not posting the same in the database. Use HashMap to update the data in your database when you modify it.
You can try the below code:
button.setOnClickListerner(new View.onClickListener() {
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("queue");
reference.child(queue_id).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
currentNum = (long) dataSnapshot.child("currentNumber").getValue();
long newValue = currentNum + 1;
HasMap<String, Object> hashMap = new HashMap<>();
hashMap.put ("currentNumber", newValue);
reference.child(queue_id).updateChildren(hashMap);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
};
Hope this works!

You can use method transactions. Refer to this link: https://firebase.google.com/docs/database/android/read-and-write#save_data_as_transactions"
private void onStarClicked(DatabaseReference postRef) {
postRef.runTransaction(new Transaction.Handler() {
#Override
public Transaction.Result doTransaction(MutableData mutableData) {
Post p = mutableData.getValue(Post.class);
if (p == null) {
return Transaction.success(mutableData);
}
if (p.stars.containsKey(getUid())) {
// Unstar the post and remove self from stars
p.starCount = p.starCount - 1;
p.stars.remove(getUid());
} else {
// Star the post and add self to stars
p.starCount = p.starCount + 1;
p.stars.put(getUid(), true);
}
// Set value and report transaction success
mutableData.setValue(p);
return Transaction.success(mutableData);
}
#Override
public void onComplete(DatabaseError databaseError, boolean b,
DataSnapshot dataSnapshot) {
// Transaction completed
Log.d(TAG, "postTransaction:onComplete:" + databaseError);
}
});
}

How to read data from RecyclerView and make comparison?

Hi I want to read the display data from RecyclerView and make comparison.
This my layout for the activity:
What I want to do is to read all data from RecyclerView and compare with Daily Calorie Suggestion.
After reading all data, I need to make comparisons on how many times the user have taken above, less or sufficient total calories as shown in the "Analysis of Total Calories Consumed of Last 7 Days"
The code:
#Override
protected void onStart() {
Query query = ref.orderByChild("timeStamp").limitToLast(7).endAt(Date);
super.onStart();
if (query != null) {
query .addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
userHighlights = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
userHighlights.add(ds.getValue(HighightsModel.class));
requiredCalorieRef = FirebaseDatabase.getInstance().getReference("Users").child(FirebaseAuth.getInstance().getCurrentUser().getUid());
requiredCalorieRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
String userCalorieSuggestion = String.valueOf((dataSnapshot.child("daily calorie").getValue()));
int daily_calorie = Integer.parseInt(userCalorieSuggestion);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
HighlightsAdapter highlightsAdapter = new HighlightsAdapter(userHighlights);
highlightsRV.setAdapter(highlightsAdapter);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Toast.makeText(UserNewHighlights.this, databaseError.getMessage(),
Toast.LENGTH_SHORT).show();
}
});
}
}
This is my firebase:
Do I have to write a new code to solve this problem or else? Any help will be much appreciated. Thanks

As #MasoudDarzi mentioned, it's not related to the RecyclerView.
You can try something like this:
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
userHighlights = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
userHighlights.add(ds.getValue(HighightsModel.class));
requiredCalorieRef = FirebaseDatabase.getInstance().getReference("Users").child(FirebaseAuth.getInstance().getCurrentUser().getUid());
requiredCalorieRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
String userCalorieSuggestion = String.valueOf((dataSnapshot.child("daily calorie").getValue()));
int daily_calorie = Integer.parseInt(userCalorieSuggestion);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
HighlightsAdapter highlightsAdapter = new HighlightsAdapter(userHighlights);
highlightsRV.setAdapter(highlightsAdapter);
// do calculation here with userHighlights
int countExceeded = 0, countBelow = 0, countSufficient = 0;
for (HighightsModel h : userHighlights) {
if (h.totalCalorie > daily_calorie) {
countExceeded++;
} else if (h.totalCalorie < daily_calorie) {
countBelow++;
} else {
countSufficient++;
}
}
// update your TextView with the count numbers
// todo
}
}

so The brute force solution is to have a for in your data after getting the 7 days average.
for (your 7 days data){
// check if your data is lower or higher than the average
// and store number of higher or lower
}
looking for a better solution?

I have solved my problem by adding another child at History node. Whereby, previously I have only these for History :
but I add new child which is called STATUS, the status is updated from previous activity as seen the pic below:
so what I did for the code is :
private void upDateAnalysisAbove() {
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("History");
DatabaseReference mRef = ref.child(FirebaseAuth.getInstance().getCurrentUser().getUid());
Query mQuery = mRef.orderByChild("status").equalTo("ABOVE").limitToLast(7);
mQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String value = String.valueOf(dataSnapshot.getChildrenCount());
int values = Integer.parseInt(value);
txt_above_output.setText(values + " times(s)");
upDateAnalysisLess(values);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
//LESS
private void upDateAnalysisLess(int values) {
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("History");
DatabaseReference mRef = ref.child(FirebaseAuth.getInstance().getCurrentUser().getUid());
Query mQuery = mRef.orderByChild("status").equalTo("LESS").limitToFirst(7);
mQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String valueLess = String.valueOf(dataSnapshot.getChildrenCount());
int values_Less = Integer.parseInt(valueLess);
if (values_Less == 0){
txt_less_output.setText(values_Less + " times(s)");
}
if (values > values_Less){
int finalCount = values - values_Less ;
txt_less_output.setText(finalCount + " times(s)");
}
if (values <values_Less){
int finalCount = values_Less - values ;
txt_less_output.setText(finalCount + " times(s)");
}
updateSuff();
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
//SUFFICIENT
private void updateSuff() {
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("History");
DatabaseReference mRef = ref.child(FirebaseAuth.getInstance().getCurrentUser().getUid());
Query mQuery = mRef.orderByChild("status").equalTo("SUFFICIENT").limitToFirst(7);
mQuery.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String value = String.valueOf(dataSnapshot.getChildrenCount());
int suffValue = Integer.parseInt(value);
if (suffValue == 0) {
txt_sufficient_output.setText(suffValue + " times(s)");
}
if (suffValue != 0){
txt_sufficient_output.setText(suffValue + " times(s)");
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
Here is the output:
credit to this post that helped me a lot, and thanks for those who tried to help me.

retrieve data from firebase using getUid() in a alertDialog box

Want to retrieve username and its contact number from the firebase database. I tried doing it but in the logcat it throws an Null Pointer
Logcat:-
Process: com.example.bhavya.epark, PID: 27351
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.bhavya.epark.userreg.getName()' on a null object reference
at com.example.bhavya.epark.MapSelect$1$1.onDataChange(MapSelect.java:51)
at com.google.firebase.database.obfuscated.zzap.zza(com.google.firebase:firebase-database##16.0.3:75)
at com.google.firebase.database.obfuscated.zzca.zza(com.google.firebase:firebase-database##16.0.3:63)
at com.google.firebase.database.obfuscated.zzcd$1.run(com.google.firebase:firebase-database##16.0.3:55)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
MapSelect.java
mAuth = FirebaseAuth.getInstance();
udetail = FirebaseDatabase.getInstance();
DatabaseReference databaseReference = udetail.getReference(mAuth.getUid());
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
userreg userprofile = dataSnapshot.getValue(userreg.class);
alertDialog1.setMessage("Name is:" + userprofile.getName());
alertDialog1.setMessage("Your Contact No:" + userprofile.getPnum());
alertDialog1.setMessage("Your Vehicle No is:" + userprofile.getVeclno());
alertDialog1.show();
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(MapSelect.this,databaseError.getCode(),Toast.LENGTH_SHORT).show();
}
});
userreg.java
package com.example.bhavya.epark;
public class userreg {
public String name,mailid,pnum,veclno;
public userreg(){
}
public userreg(String name,String mailid,String pnum,String veclno){
this.name=name;
this.mailid=mailid;
this.pnum=pnum;
this.veclno=veclno;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getMailid() {
return mailid;
}
public void setMailid(String mailid) {
this.mailid = mailid;
}
public String getPnum() {
return pnum;
}
public void setPnum(String pnum) {
this.pnum = pnum;
}
public String getVeclno() {
return veclno;
}
public void setVeclno(String veclno) {
this.veclno = veclno;
}
}
Database Strucure:-
Image reference
https://i.stack.imgur.com/owWJr.jpg

You are pointing towards a wrong database reference. Your database has a node named Users but your code doesn't have this.
Instead of
DatabaseReference databaseReference = udetail.getReference(mAuth.getUid());
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
userreg userprofile = dataSnapshot.getValue(userreg.class);
alertDialog1.setMessage("Name is:" + userprofile.getName());
alertDialog1.setMessage("Your Contact No:" + userprofile.getPnum());
alertDialog1.setMessage("Your Vehicle No is:" + userprofile.getVeclno());
alertDialog1.show();
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(MapSelect.this,databaseError.getCode(),Toast.LENGTH_SHORT).show();
}
});
Use
DatabaseReference databaseReference = udetail.getReference().child("Users");
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot messageSnapshot: dataSnapshot.getChildren()) {
userreg userprofile = messageSnapshot.getValue(userreg.class);
Log.v("info",String.valueOf(userprofile));
}
//Do whatever you like to do with your data here
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(MapSelect.this,databaseError.getMessage(),Toast.LENGTH_SHORT).show();
}
});

Firebase DataSnapshot Null values

My app allows you to add a Player to a node, once they have been added I am using the below method to search by phoneNum to see if that player exists in the 'users' node.
Where I am having trouble is that I need to be able to access the values from the datasnapshot for the user within the found matching node. e.g.return the value of the user id. When I attempt this it keeps showing as a null value and when I try to log to the console it complains that it is a null value which doesn't make sense as the if statement should take care of this.
The method is able to find if a player exists in the the users node and displays a Toast message to indicate this.
Code:
public void checkPlayerNum(final String phoneNum) {
DatabaseReference mDatabaseReference =
FirebaseDatabase.getInstance().getReference().child("users");
if (!TextUtils.isEmpty(phoneNum)) {
final Query phoneNumReference = mDatabaseReference.orderByChild("phoneNum").equalTo(phoneNum);
ValueEventListener phoneNumValueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.getValue() != null) {
// String key = String.valueOf(dataSnapshot.getValue());
User mUser = dataSnapshot.getValue(User.class);
String uId = mUser.getUid();
// Log.d("TAG",uId);
Toast.makeText(getApplicationContext(), "* found **"+ uId , Toast.LENGTH_LONG).show();
} else {
Toast.makeText(getApplicationContext(), "****NOT FOUND****", Toast.LENGTH_LONG).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
phoneNumReference.addListenerForSingleValueEvent(phoneNumValueEventListener);
} else {
Log.e("Error","phoneNum is null");
}
}

final Query query = mFirebaseDatabase.orderByChild("phoneNum").equalTo("userPhoneNumber");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
//here means the value exist
//do whatever you want to do
} else {
//here means the value not exist
//do whatever you want to do
}
}
#Override
public void onCancelled(FirebaseError firebaseError) {
}
});
Use this to check whether the data exist or not.

you need to do this at two steps , first check if the user exists. then you get user info by your userId.
DatabaseReference mDatabaseReference;
public void checkPlayerNum(final String phoneNum,final String userId) {
mDatabaseReference =
FirebaseDatabase.getInstance().getReference().child("users");
if (!TextUtils.isEmpty(phoneNum)) {
final Query phoneNumReference = mDatabaseReference.orderByChild("phoneNum").equalTo(phoneNum);
ValueEventListener phoneNumValueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.getValue() != null) {
// user exists
getUserInf(userId);
} else {
Toast.makeText(getApplicationContext(), "****NOT FOUND****", Toast.LENGTH_LONG).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
phoneNumReference.addListenerForSingleValueEvent(phoneNumValueEventListener);
} else {
Log.e("Error","phoneNum is null");
}
}
get user info by userId. mDatabaseReference is the same as before . define it as member field .
void getUserInf(String userId) {
userValueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// get user data
User mUser = dataSnapshot.getValue(User.class);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
};
mDatabaseReference.child(userId).addListenerForSingleValueEvent(userValueEventListener);
}
your user Pojo should be like below.
public class User {
String email,name,phoneNum,uid;
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPhoneNum() {
return phoneNum;
}
public void setPhoneNum(String phoneNum) {
this.phoneNum = phoneNum;
}
public String getUid() {
return uid;
}
public void setUid(String uid) {
this.uid = uid;
}
}

Thanks everybody I managed to achieve it by using childEventListener
public void checkingNumber(final String phoneNum){
DatabaseReference mDatabaseReference =
FirebaseDatabase.getInstance().getReference().child("users");
final Query query = mDatabaseReference;
query.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.getValue() != null) {
// String key = String.valueOf(dataSnapshot.getValue());
User mUser = dataSnapshot.getValue(User.class);
// String uId = mUser.getUid();
// usersDatabase.child(mUser.getUid());
// Log.d("TAG",uId);
if(mUser.getPhoneNum().equals(phoneNum)) {
String uId= mUser.getUid();
String email = mUser.getEmail();
String name = mUser.getName();
Toast.makeText(getApplicationContext(), "* found **" + " " + uId + " " + " " + email + " " + name, Toast.LENGTH_LONG).show();
}
} else {
Toast.makeText(getApplicationContext(), "****NOT FOUND****", Toast.LENGTH_LONG).show();
}
}
#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) {
}
});
}

Firebase like counter

I'm confused here and really at the end on the line, I have set up a like function in my project. if a user presses the like button once, the like counter update from 0 to 1(liked) and the like imageButton(change color) updates successful. if pressed twice the counter updates from 1 to 0(unlike) successful.
The problem is when a different user also press the like button to like the same post, the like counter does not update from 1 to 2. Please help. I hope this is clear. Below is the code.
viewHolder.mLikebtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mProcessLike = true;
mDatabaseLikeCount = FirebaseDatabase.getInstance().getReference().child("Notes").child(post_key).child("likecount");
mDatabaseLikeCount.keepSynced(true);
mDatabaseLike.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (mProcessLike) {
if (dataSnapshot.child(post_key).hasChild(auth.getCurrentUser().getUid())) {
Log.i("D Diary", "User has already Liked. So it can be considered as Unliked.");
mDatabaseLike.child(post_key).child(auth.getCurrentUser().getUid()).removeValue();
mDatabaseLikeCount.setValue(likeCount = likeCount - 1 );
mProcessLike = false;
} else {
Log.i("D Diary", "User Liked");
mDatabaseLike.child(post_key).child(auth.getCurrentUser().getUid()).setValue(auth.getCurrentUser().getDisplayName());
mDatabaseLikeCount.setValue(likeCount = likeCount + 1 );
Log.i(dataSnapshot.getKey(), dataSnapshot.getChildrenCount() + "Count");
mProcessLike = false;
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});

This should work. You should use a transaction to increment or reduce a value that multiple people will be interacting with.
if (dataSnapshot.child(post_key).hasChild(auth.getCurrentUser().getUid())) {
Log.i("D Diary", "User has already Liked. So it can be considered as Unliked.");
mDatabaseLike.child(post_key).child(auth.getCurrentUser().getUid()).removeValue();
updateCounter(false);
mProcessLike = false;
} else {
Log.i("D Diary", "User Liked");
mDatabaseLike.child(post_key).child(auth.getCurrentUser().getUid()).setValue(auth.getCurrentUser().getDisplayName());
updateCounter(true)
Log.i(dataSnapshot.getKey(), dataSnapshot.getChildrenCount() + "Count");
mProcessLike = false;
}
With updateCounter:
private void updateCounter(bool increment) {
mDatabaseLikeCount.runTransaction(new Transaction.Handler() {
#Override
public Transaction.Result doTransaction(MutableData mutableData) {
if (mutableData.getValue() != null) {
int value = mutableData.getValue(Integer.class);
if(increment) {
value++;
} else {
value--;
}
mutableData.setValue(value);
}
return Transaction.success(mutableData);
}
#Override
public void onComplete(DatabaseError databaseError, boolean b,
DataSnapshot dataSnapshot) {
// Transaction completed
Log.d(TAG, "likeTransaction:onComplete:" + databaseError);
}
});
}
Firebase Transactions