Get value from Firebase while extending ArrayList

Question

I'm trying to work with Firebase and Lists.

My objects contains a class extending ArrayList such as:

MyClass {
    // other fields here
    public static class List extends ArrayList<Foo> {};
}

If I try to upload a List item to Firebase database, it works out of the box and no problem are faced.

The problem come when I try to retrieve these Lists from the server, such as:

MyClass mMyClass = dataSnapshot.getValue(MyClass.class);

This throws an exception saying

com.google.firebase.database.DatabaseException: Can't convert object of type java.util.ArrayList to type mypackage.MyClass$List

The only possible thing working for me is to revert back to ArrayList<Foo> instead of extending it from another class.

Is there any other possible way to cast without problems? Thanks in advance.

score 1 · Accepted Answer · answered Mar 08 '17 at 17:42

1

Try using a GenericTypeIndicator to read the list data as a generic collection:

GenericTypeIndicator<MyClass.List> t = new GenericTypeIndicator<MyClass.List>() {};
MyClass.List mList = dataSnapshot.getValue(t);

I'm not sure whether this will work with an inner class. You may need to declare List as its own stand-alone type. See this question for more examples.

answered Mar 08 '17 at 17:42

Travis Christian

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Thank you! Exactly what I was looking for – Lampione Mar 09 '17 at 06:05
I'm curious how this worked out for you with your generic list being a member of the class you want to read. I looked for a solution but only found [this unanswered question.](http://stackoverflow.com/q/41948309/213156) – Travis Christian Mar 09 '17 at 15:39

score 0 · Answer 2 · answered Mar 06 '17 at 11:14

0

Did you try getting the value as ArrayList and then casting it to your class. Something like:

MyClass mMyClass = (MyClass) dataSnapshot.getValue(ArrayList.class);

answered Mar 06 '17 at 11:14

Hristo Stoyanov

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My problem is that the class 'List' is inside the class which I'm passing to the 'getValue()' method – Lampione Mar 06 '17 at 11:25

score 0 · Answer 3 · answered Mar 06 '17 at 11:21

0

User addEventValueListener for getting arraylist of particular reference

answered Mar 06 '17 at 11:21

Chirag.T

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I'm sorry, I cutted it away from the post since I thought it was boilerplate, I'm already doing this in a ValueEventListener. – Lampione Mar 06 '17 at 11:22
then what happen..? – Chirag.T Mar 06 '17 at 11:23
As the question say, I'm getting a DatabaseException since firebase is trying to cast an ArrayList to a List class which is extending ArrayList – Lampione Mar 06 '17 at 11:25
use direct `dataSnapshot.getValue(List.class);` – Chirag.T Mar 06 '17 at 11:28

Get value from Firebase while extending ArrayList

3 Answers3