I want to check if an id already exists before inserting it (prevent updating an already existing id).
This is the code I have so far:
database.child(id).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Toast.makeText(getApplicationContext(), "it exists.", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(getApplicationContext(), "it's OK.", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(getApplicationContext(), databaseError.getMessage(), Toast.LENGTH_SHORT).show();
}
});
The problem is that, when the id does not exists, it shows both toasts. But, when it does exist, it only shows the "it exists." one.
How can I show the "it exists." toast only when the id exists / How can I prevent the "it exist." toast from showing when the id doesn't exist?
EDIT:
Firebase database structure:
-DATABASE
-ID
-NAME
-DESCRIPTION
Try like this
database.child(id).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.getValue()!=null) {
Toast.makeText(getApplicationContext(), "it exists.", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(getApplicationContext(), "it's OK.", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(getApplicationContext(), databaseError.getMessage(), Toast.LENGTH_SHORT).show();
}
});
Please do this:
database.child(id).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Toast.makeText(getApplicationContext(), "it exists.", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(getApplicationContext(), "it's OK.", Toast.LENGTH_SHORT).show();
}
}
Since the valueeventListener will iterate through all the child(id) thus you will get both Toast the one for exists and for does not exists.
Use the addListenerForSingleValueEvent then it will only iterate in the id that you specify before.
Try replacing your addValueEventListener Method with addListenerForSingleValueEvent .
Because possibly addValueEventListener will be called twice due to change in data Thats the reason it first shows Exist and than not Exist for same id.
For addListenerForSingleValueEvent firebase states that it supposed to:
Read Data Once.
In some cases it may be useful for a callback to be called once and
then immediately removed. We've created a helper function to make this
easy:
Related
My Firebase Realtime Database has been built by loading an object of the Java class HashMap. In my Android Studio app I'm trying to write a method that takes a String (the key) as input, searches through the database and if the string is found it returns the associated Float (the value), otherwise it returns 0. How can I do this? Any help would be really appreciated!
EDIT: I've tried to follow the suggestions, adapting them to my particular case, but I didn't manage to solve the problem yet.
I wrote the following code in MainActivity:
DatabaseReference myRef;
Float tempValue;
#Override
protected void onCreate(Bundle savedInstanceState) {
...
myRef = FirebaseDatabase.getInstance().getReference("myRoot");
tempValue=0f;
...
}
public void retrieveValueFromDatabase(String childName, final MainActivity activity){
myRef.child(childName).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Float value=dataSnapshot.getValue(Float.class);
if (value==null){
value=0f;
}
activity.tempValue=value;
//First Toast
//Toast.makeText(activity,"tempValue = "+tempValue.toString(), Toast.LENGTH_LONG).show();
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
});
}
public void useValues(){
retrieveValueFromDatabase(childName,this);
//Second Toast
//Toast.makeText(this,"tempValue = "+tempValue.toString(), Toast.LENGTH_LONG).show();
//code using tempValue from here
...
}
If I uncomment the first toast, the correct value inside tempValue is shown, but if I uncomment the second toast, the value of tempValue shown is the default one (0.0). What am I missing?
You need to use addValueEventListener to retrieve data from the database:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("myRoot").orderByChild("name").equalTo("peter");
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Log.i("Database", dataSnapshot.child("floatValue").getValue(Long.class));
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
})
Here, you add a reference to the root node, then query using equalTo() to check if name = peter exists in the database and return the float value.
You should read the guide:
https://firebase.google.com/docs/database/android/read-and-write
I am developing a chat app but when it comes to viewing friend requests to the user i face a problem that is
When I log queries of Firebase why is it not properly ordered as code ?
This is my code:
// Query for pending requests in the current user
Log.v("AAAAAA", "AAAAAA");
usersRef.child(MainActivity.currentUser.getUid()).child("inpendingfriendreq").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) { // dataSnapShot = inpendingfriendreq node
for (DataSnapshot reqDataSnapShot : dataSnapshot.getChildren()) {
U = reqDataSnapShot;
Log.v("BBBBBBBB", U.toString());
usersRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot sDataSnapshot) { // sDataSnapshot = "users" node DataSnapShot
for (DataSnapshot searchForPendingUserDS : sDataSnapshot.getChildren()) { // searchForPendingUserDS = a user from database (child node of "users" node)
Log.v("CCCCCCC", searchForPendingUserDS.toString());
if (searchForPendingUserDS.getKey().equals(U.getKey())) { // If that user's id equals pending req id
MainActivity.reqArrList.add(new FriendRequest(R.drawable.default_pp, searchForPendingUserDS.child("name").getValue(String.class)));
Log.v("DDDDDDDDD", searchForPendingUserDS.child("name").getValue(String.class));
}
}
Log.v("EEEEEEEE", MainActivity.reqArrList.toString());
//requestsPageUpdated();
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(mContext, "Error querying", Toast.LENGTH_SHORT).show();
}
});
//requestsPageUpdated();
Log.v("FFFFFFFFFF", "FFFFFFFFF");
break;
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(mContext, "Error querying", Toast.LENGTH_SHORT).show();
}
});
It should be:
AAAAAA
BBBBBB
CCCCCC
DDDDDD
CCCCCC
CCCCCC
CCCCCC
EEEEEE
FFFFFF
GGGGGG
But it shows that in the Logcat:
AAAAAA
GGGGGG
BBBBBB
FFFFFF
CCCCCC
DDDDDD
CCCCCC
CCCCCC
CCCCCC
EEEEEE
I know that event listeners are Async but what is the meaning of that ?
Does Async means that the function are waiting to be triggered like Button onClickListener or does it mean that when it's triggered it runs parallel to the main thread? so in the second case that will make sense to my problem.
Any help, please!
Im using the Android SDK for firebase database.
In the database I have a structure where I keep the messages ordered by user, that way if I need their messages I just query by user.
myDatabase -> messages -> JonDoe
-> "You forgot your mail"
-> "Buy groceries"
-> JaneDoe
-> "Dog's birthday!"
The problem is if the user doesnt exist the listener keeps waiting forever, and I want to show "You have no messages" in that case. (For example, if I query the user "CharlesDoe" in the example above)
Is there a way to check if a reference exists before/after/during a query?
try this:
DatabaseReference root =FirebaseDatabase.getInstance().getReference();
DatabaseReference user = root.child("myDatabase").child("messages");
user.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.child("CharlesDoe").exists()) {
// run some code
}else{
Toast.makeText(this,"no messages",Toast.Length_LONG).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Here it will query on node messages and then it will check if the child exists and do the required.
Try this on
DatabaseReference root =FirebaseDatabase.getInstance().getReference();
DatabaseReference user =
root.child("myDatabase").child("messages").child("CharlesDoe");
user.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.exists()) {
// run some code
}else{
Toast.makeText(this,"no messages",Toast.Length_LONG).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
I am simply trying to copy information I have saved in one Firebase location to another:
mFollowingCheck.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
#Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if (b){
mBaseRef.child(USERS_LABEL).child(mUserID).child(FOLLOWING_LABEL).child(USERS_LABEL).child(mPollCreatorID).child(DISPLAY_NAME_LABEL).setValue(mPollCreatorDisplayName);
mBaseRef.child(POLL_LABEL).child(pollID).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
mBaseRef.child(USERS_LABEL).child(mUserID).child(FOLLOWING_LABEL).child(POLL_LABEL).child(pollID).setValue(dataSnapshot);
}
#Override
public void onCancelled(DatabaseError databaseError) {
Toast.makeText(getContext(), databaseError.getCode(), Toast.LENGTH_LONG).show();
}
});
} else {
mBaseRef.child(USERS_LABEL).child(mUserID).child(FOLLOWING_LABEL).child(USERS_LABEL).child(mPollCreatorID).child(DISPLAY_NAME_LABEL).removeValue();
}
}
});
When I have this code, the app is simply crashing. There is no logging error and I am unable to pinpoint exactly what I am doing incorrectly. Essentially, I would like to know best practice for copying Firebase data.
In onDataChange() you should be storing the value of the DataSnapshot, not the Datasnapshot object itself.
Change:
setValue(dataSnapshot);
to
setValue(dataSnapshot.getValue());
Also, your code to show a Toast is wrong:
Toast.makeText(getContext(), databaseError.getCode(), Toast.LENGTH_LONG).show();
databaseError.getCode() returns an int, which means you are calling the form of makeText() that expects a string resource ID. Change to:
Toast.makeText(getContext(), databaseError.getMessage(), Toast.LENGTH_LONG).show();
I have a Firebase database that I want to retrieve the friend ID from. This works perfectly as I'm getting the right value when logging the friendUserId in the for loop. However, the log at the end of the method only displays the right value after executing the method twice. At first it displays "s", the second time it displays the string that I want. I feel like it has got something to do with processing time of the query, but I'm not sure really. How do I solve this?
public String friendUserId="s";
public void checkUserExistence() {
mDatabase.child("Users")
.orderByChild("username")
.equalTo(EmailSearchQuery)
.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
friendUserId = childSnapshot.getKey();
Log.d("dwada",friendUserId);
}
} else
Toast.makeText(AddAFriend.this, "Gebruiker niet gevonden", Toast.LENGTH_LONG);
}
#Override
public void onCancelled(DatabaseError firebaseError) {
Log.e("MainActivity", "onCancelled", firebaseError.toException());
}
});
Log.d("dwada",friendUserId);
}