I'm trying to learn how to use Firebase, and decided to make a simple android application that uses the Firebase RealTime Database. The game requires a host who hosts a lobby, and players who can join that lobby. I made a host class that has a bunch of data types, among which is a list (the game involves using hints given to players by the host). I'm running into problems when I try to read from the database.
My lobby is a listview that I want to populate with a list of hosts in the database, but when I try to read from it I get this nasty error:
com.google.firebase.database.DatabaseException: Class java.util.List has generic type parameters, please use GenericTypeIndicator instead
I know that there are other questions about the same error, but I couldn't apply those answers with much success. I'm quite new to android development and would greatly appreciate any help.
Here is my user-defined class:
public class HostPlayer {
private String hostName;
private String photoUrl;
private String primaryHint;
List<String> hints = new ArrayList<String>();
private int numHints;
private int numTime;
private boolean inProgress = false;
public HostPlayer() {
}
public HostPlayer(String hostName, int numHints, int numTime, List<String> hints, String primaryHint, String photoUrl) {
this.hostName = hostName;
this.numHints = numHints;
this.numTime = numTime;
this.hints = hints;
this.primaryHint = primaryHint;
this.photoUrl = photoUrl;
this.inProgress = false;
}
public void setPhotoUrl(String photoUrl) {this.photoUrl = photoUrl;}
public void setPrimaryHint(String primaryHint) {this.primaryHint = primaryHint;}
public void setHints(List hints) {this.hints = hints;}
public String getHostName() {return this.hostName;}
public int getNumHints() {return this.numHints;}
public int getNumTime() {return this.numTime;}
public String getPrimaryHint() {return this.primaryHint;}
public List getHints() {return this.hints;}
public void setInProgress() {this.inProgress = true;}
public boolean getInProgress() {return this.inProgress;}
}
Here is my code where I read from the database:
public class JoinGame extends AppCompatActivity {
ListView lv;
private FirebaseDatabase pFireBaseDatabase;
private DatabaseReference pDatabaseReference;
private ChildEventListener pChildEventListener;
List<HostPlayer> hostPlayerList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_join_game);
pFireBaseDatabase = FirebaseDatabase.getInstance();
pDatabaseReference = pFireBaseDatabase.getReference().child("hosts");
pChildEventListener = new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
HostPlayer hostPlayer = snapshot.getValue(HostPlayer.class); //this is where the error happens
hostPlayerList.add(hostPlayer);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
};
pDatabaseReference.addChildEventListener(pChildEventListener);
lv = findViewById(R.id.listView_hosts);
ArrayAdapter<HostPlayer> hostPlayerArrayAdapter = new ArrayAdapter<HostPlayer>(
this, android.R.layout.simple_list_item_1, hostPlayerList
);//making an arrayAdapter out of the list of HostPlayer objects
lv.setAdapter(hostPlayerArrayAdapter);
}
}
This is what the database JSON is structured like:
{
"hosts" : {
"some-data-key" : {
"hints" : [ "first hint", "second hint" ],
"hostName" : "mom",
"inProgress" : false,
"numHints" : 3,
"numTime" : 30,
"primaryHint" : "Living Room"
}
},
"players" : {
"another-data-key" : {
"hostName" : "firstName",
"inProgress" : false,
"numHints" : 0,
"numTime" : 0
}
}
}
I understand that the list "hints" is causing this error, but still don't understand why and how I can fix it. I would greatly appreciate any explanations and/or solutions. Thanks for your time and help.
Edit: I forgot to paste the logcat, here it is:
2021-10-23 16:11:20.732 21137-21137/com.example.treasurehunt E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.treasurehunt, PID: 21137
com.google.firebase.database.DatabaseException: Class java.util.List has generic type parameters, please use GenericTypeIndicator instead
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:224)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(CustomClassMapper.java:179)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(CustomClassMapper.java:48)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:593)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:563)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:433)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)
at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)
at com.example.treasurehunt.JoinGame$1.onChildAdded(JoinGame.java:41)
at com.google.firebase.database.core.ChildEventRegistration.fireEvent(ChildEventRegistration.java:79)
at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I've adapted the answer Frank and Alex mentioned in their comments. And it seems to be working in your situation. Instead of directly using
snapshot.getValue(HostPlayer.class);
use a GenericTypeIndicator like this;
pChildEventListener = new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
GenericTypeIndicator<HostPlayer> t = new GenericTypeIndicator<HostPlayer>() {};
HostPlayer hostPlayer = snapshot.getValue(t);//I was able to get the list without an error
...
}
...
};