Asynchronous Firebase API - Firebase Realtime Database and Android

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Recommends Alex Mamo · 2018-03 · Stack Overflow · on “Store Value of Key to Global Variable Firebase Android 'pathString' in child()”

You cannot declare Common.workerType as o global variable and simply use it outside the onDataChange() method because it will always be null . This is happening because this method has an asynchronous behaviour, which means that is called even before you are getting the data from the database. Even if this would have been possible, as I see in your code, you are looping through the entire dataSnapshot object using getChildren() method and every value that you get you assign it to the same variable. In this case, you variable will always have the value of last iteration. A quick solve for the first problem would be, to use the value of Common.workerType only inside the onDataChange() method o

Recommends Alex Mamo · 2018-05 · Stack Overflow · on “Firebase can't save retrieved data to ArrayList”

You cannot return something now that hasn't been loaded yet. In other words, you cannot simply return the profiles list outside the onDataChange() method because it will always be empty due to the asynchronous behavior of this method. This means that by the time you are trying to return that result outside that method, the data hasn't finished loading yet from the database and that's why is not accessible. A quick solution for this problem would be to use the profiles list only inside the onDataChange() method, otherwise I recommend you see the last part of my answer from this post [LINK] in which I have explained how it can be done using a custom callback. You can also take a look at this v

Recommends Alex Mamo · 2018-05 · Stack Overflow · on “How to retrieve data from ValueEventListener Firebase”

You cannot return something now that hasn't been loaded yet. With other words, you cannot simply use the amount object outside the onDataChange() method because it will always be null due the asynchronous behaviour of this method. This means that by the time you are trying to use that result outside that method, the data hasn't finished loading yet from the database and that's why is not accessible. A quick solve for this problem would be to use those results only inside the onDataChange() method or if you want to use it outside, I recommend you see the last part of my anwser from this post [LINK] in which I have explained how it can be done using a custom callback. You can also take a look

Recommends Alex Mamo · 2018-05 · Stack Overflow · on “Error while fetching datasnapshot from firebase -> java.lang.NumberFormatException: Invalid int: ""”

You cannot use something now that hasn't been loaded yet. With other words, you cannot simply create the freading variable as a global variable and use the result that you are getting from the database outside the onDataChange() method because it will always be null , due the asynchronous behaviour of this method. This means that by the time you are trying to use that result outside that method, the data hasn't finished loading yet from the database and that's why is not accessible. A quick solve for this problem would be to use that results only inside the onDataChange() method, or if you want to use it outside, I recommend you see the last part of my anwser from this post [LINK] in which I

Recommends Alex Mamo · 2018-05 · Stack Overflow · on “Firebase - retrieving data by value to an outside variable”

You cannot return something now that hasn't been loaded yet. With other words, you cannot simply return the first element of your array exists[0] , outside the onDataChange() method because it will always be null due the asynchronous behaviour of this method. This means that by the time you are trying to use that result outside that method, the data hasn't finished loading yet from the database and that's why is not accessible. A quick solve for this problem would be to use exists[0] only inside the onDataChange() method, or if you want to use it outside, I recommend you dive into the asynchronous world and see the last part of my anwser from this post [LINK] in which I have explained how it

Recommends Alex Mamo · 2018-05 · Stack Overflow · on “Method returning value before code can run to update the value”

You cannot return something now that hasn't been loaded yet. With other words, you cannot simply use the authSuccess object outside the onComplete() method because it will always be null due the asynchronous behaviour of this method. This means that by the time you are trying to return that result outside that method, the data hasn't finished loading yet from the database and that's why is not accessible. A quick solve for this problem would be to use the value of authSuccess only inside the onComplete() method, otherwise I recommend you see the last part of my anwser from this post [LINK] in which I have exaplined how it can be done using a custom callback. You can also take a look at this

Recommends Alex Mamo · 2018-07 · Stack Overflow · on “Not able to access inner class data from outer class in Android”

Firebase APIs are asynchronous , meaning that onDataChange() method returns immediately after it's invoked, and the callback from the Task it returns will be called sometime later. There are no guarantees about how long it will take. So it may take from a few hundred milliseconds to a few seconds before that data is available. Because that method returns immediately, the value of your userName variable you're trying to use outside the onDataChange() method, will not have been populated from the callback yet. Basically, you're trying to return a value synchronously from an API that's asynchronous. That's not a good idea. You should handle the APIs asynchronously as intended. A quick solution

Recommends Alex Mamo · 2018-08 · Stack Overflow · on “Firebase onDataChange method increase value”

Firebase APIs are asynchronous , meaning that the onDataChange() method that you are talking about returns immediately after it's invoked and the callback from the Task it returns, will be called some time later. There are no guarantees about how long it will take, it may take from a few hundred milliseconds to a few seconds before that data is available. Because that method returns immediately, the value of your rat variable you're trying to use it outside the onDataChange() method, will not have been populated from the callback yet. Basically, you're trying to return the value of rat synchronously from an API that's asynchronous. That's not a good idea. You should handle the APIs asynchron

Recommends Alex Mamo · 2018-08 · Stack Overflow · on “Android spinner populated with Firebase database not selecting the item”

You cannot pass the categories list that you get from the database to your adapter outside the callback because it will always be empty. That's why you have that empty screen. Note, that onChildAdded() method has an asynchronous behavior. A quick solve for this problem would be to move the declaration of your adapter inside the onDataChange() method and then just notify the adapter. For more details I recommend you see my anwser from this post [LINK] in which I have explained how you can get an object outside the callback. You can also take a look at this video [this video] for a better understanding.

Recommends Alex Mamo · 2018-09 · Stack Overflow · on “Android/Firebase - How to add retrieved data to an ArrayList”

You can use addChildEventListener or you can use addListenerForSingleValueEvent , as in my code below: ValueEventListener valueEventListener = new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { List<String> arrayList = new ArrayList<>(); for(DataSnapshot ds : dataSnapshot.getChildren()) { Question question = ds.getValue(Question.class); arrayList.add(question.title); } //Do what you need to do with your arrayList } @Override public void onCancelled(@NonNull DatabaseError databaseError) { Log.d(TAG, databaseError.getMessage()); } }; refQuestions.addListenerForSingleValueEvent(valueEventListener); As you can see, a quick solve for this problem is to use