Android Firebase无法将类型java.util.HashMap的值转换为String [英] Android Firebase Failed to convert value of type java.util.HashMap to String

问题描述

我正在尝试在片段上使用数组适配器使用listview，但是当尝试使用教程进行操作时，每次打开该特定片段时，它都会崩溃.我正在尝试将Firebase上的数据显示到列表视图中，但是每次我打开它时都会崩溃.

I'm trying to use the listview using array adapter on my fragment but when trying to do it using the tutorial, It crashes every time i open that specific fragment. I'm trying to show the data on my firebase into the listview but it crashes every time i open it.

这是我的数据库

从图片中我的计划是仅显示用户的电子邮件和姓名，而不包括类型，但我稍后再讲.

From the picture My plan is to only show the email and name of the user and not to include the type but I'll do that later.

这是我的代码

public class memberFragment extends Fragment {
private ListView mylistView;
private DatabaseReference mDatabase;
ArrayList<String> myArrayList = new ArrayList<>();
FirebaseDatabase myFirebase;


public memberFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_member2, container, false);
    mDatabase = FirebaseDatabase.getInstance().getReference().child("Accounts").child("Users");
    final ArrayAdapter<String> myArrayAdapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,myArrayList);
     mylistView = (ListView)view.findViewById(R.id.listView);
     mylistView.setAdapter(myArrayAdapter);


    mDatabase.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            String myChildValues = dataSnapshot.getValue(String.class);
            myArrayList.add(myChildValues);
            myArrayAdapter.notifyDataSetChanged();


        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            myArrayAdapter.notifyDataSetChanged();

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
    // Inflate the layout for this fragment
    return view;

任何想法可能是导致问题的原因吗?我试图搜索并发现它与哈希图或地图有关，但是我不知道如何将其放在数组中?

Any ideas what might be causing the problem? I tried to searched and found out its related to hashmap or map, but I have no idea how to put it on my array?

推荐答案

可以使用模型类来实现此目的，或者可以使用最简单的方法使用String类.为此，您可以使用以下代码:

The can use a model class in order to achieve this or you can use a simplest way, using the String class. For that, you can use the following code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference usersRef = rootRef.child("Accounts").child("Users");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String email = ds.child("email").getValue(String.class);
            String name = ds.child("name").getValue(String.class);
            Log.d("TAG", email + " / " + name);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
usersRef.addListenerForSingleValueEvent(eventListener);

您的输出将是:

[e-mail] / idk
//and so on

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