Question

我尝试编写一个片段来列出来自firebase的用户，但是，它无法显示列表，然后分解应用程序。

任何人都可以帮我解决这个问题吗？下面是代码：

public class FriendListFragment extends Fragment{

private ArrayList<String> mUsernames = new ArrayList<>();

private ListView mFriendList;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_friendlist,container,false);

    //FirebaseDatabase mRef = FirebaseDatabase.getInstance();

    DatabaseReference mRef = FirebaseDatabase.getInstance().getReference();
            //.getReferenceFromUrl("https://game-frontier.firebaseio.com/");

    mFriendList = (ListView) rootView.findViewById(R.id.friendList);

    final ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, mUsernames);


    //final ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(android.R.layout.simple_list_item_1, mUsernames);
    //mFriendList.setAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, mUsernames));

    mFriendList.setAdapter(arrayAdapter);

    mRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            String value = dataSnapshot.getValue(String.class);
            mUsernames.add(value);
            arrayAdapter.notifyDataSetChanged();

        }

        @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) {

        }
    });

    return rootView;

}
}

错误logcat如下：

D/FA: Connected to remote service
V/FA: Processing queued up service tasks: 1
W/PathParser: Points are too far apart 4.000000596046461
D/AndroidRuntime: Shutting down VM
E/UncaughtException: com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String
                     at com.google.android.gms.internal.zzbtg.zzaF(Unknown Source)
                     at com.google.android.gms.internal.zzbtg.zzb(Unknown Source)
                     at com.google.android.gms.internal.zzbtg.zza(Unknown Source)
                     at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
                     at game_frontier_fragment.FriendListFragment$1.onChildAdded(FriendListFragment.java:58)
                     at com.google.android.gms.internal.zzbox.zza(Unknown Source)
                     at com.google.android.gms.internal.zzbqx.zzZS(Unknown Source)
                     at com.google.android.gms.internal.zzbra$1.run(Unknown Source)
                     at android.os.Handler.handleCallback(Handler.java:739)
                     at android.os.Handler.dispatchMessage(Handler.java:95)
                     at android.os.Looper.loop(Looper.java:234)
                     at android.app.ActivityThread.main(ActivityThread.java:5526)
                     at java.lang.reflect.Method.invoke(Native Method)
                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

D / FA：记录事件（FE）：_ae，Bundle [{_ o = crash，_sc = MainActivity，_si = -9082221781176828208，timestamp = 1487772508300，fatal = 1}] E / AndroidRuntime：致命异常：主要处理：com.gamefrontier.jk.gamefrontier，PID：14745 com.google.firebase.database.DatabaseException：无法将java.util.HashMap类型的值转换为String 在com.google.android.gms.internal.zzbtg.zzaF（未知来源）在com.google.android.gms.internal.zzbtg.zzb（未知来源）在com.google.android.gms.internal.zzbtg.zza（未知来源）在com.google.firebase.database.DataSnapshot.getValue（未知来源） at game_frontier_fragment.FriendListFragment $ 1.onChildAdded（FriendListFragment.java:58）在com.google.android.gms.internal.zzbox.zza（未知来源）在com.google.android.gms.internal.zzbqx.zzZS（未知来源）在com.google.android.gms.internal.zzbra $ 1.run（未知来源）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:234）在android.app.ActivityThread.main（ActivityThread.java:5526） at java.lang.reflect.Method.invoke（Native Method）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616） I / DpmTcmClient：RegisterTcmMonitor来自：com.android.okhttp.TcmIdleTimerMonitor I /处理：发送信号。 PID：14745 SIG：9 申请已终止。

片段无法显示，应用程序将崩溃

0 个答案: