android-从数据库显示数据到 ListView 并每次刷新

Question

我在我的 Fragment 中使用了一个 ListView。我还有一个 EditText 和一个 Button。所以每次我点击我的 Button 时，我都会获取我的 EditText 的内容 每次我在我的列表中添加 friend 时，如何刷新我的 ListView数据库，而不必进入另一个 Fragment 并返回。

这是我的 fragment 。

public class ContactFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_contact, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        ListView list = getView().findViewById(R.id.contactframe);
        auth = FirebaseAuth.getInstance();
        final User user = new User();
        bouton = getView().findViewById(R.id.search_btn);
        email = getView().findViewById(R.id.search_field);
        bouton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!email.getText().toString().trim().equals(auth.getCurrentUser().getEmail().toString().trim())) {
                    user.addFriend(auth.getCurrentUser().getUid(), email.getText().toString().trim());
                    email.setText("");
                } else {
                    Toast.makeText(getActivity(), "Action refusé", Toast.LENGTH_LONG).show();
                }
            }
        });

        contactList = new ArrayList<User>();
        mDatabase = FirebaseDatabase.getInstance().getReference("User").child(auth.getCurrentUser().getUid().toString())
                .child("contact");
        mDatabase.addListenerForSingleValueEvent(valueEventListener);

        adaptor = new ContactAdaptor(getActivity(), contactList);
        list.setAdapter(adaptor);
    }

    ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            contactList.clear();
            if (dataSnapshot.exists()) {
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                    User ami = snapshot.getValue(User.class);
                    contactList.add(ami);
                }

                adaptor.notifyDataSetChanged();
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };
}

还有我的适配器

public class ContactAdaptor extends ArrayAdapter<User> {
    private LayoutInflater mInflater;
    ArrayList<User> myList;

    public ContactAdaptor(FragmentActivity activity, List<User> myList) {
        super(activity, 0, myList);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        User item = (User) getItem(position);
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.list_contact, parent, false);
        }

        TextView username = (TextView) convertView.findViewById(R.id.text_view_contact_username);
        TextView email = (TextView) convertView.findViewById(R.id.contact_email);
        username.setText(item.username);
        email.setText(item.email);

        return convertView;
    }
}

布局文件是

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <!-- Editext for Search -->
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <EditText
            android:id="@+id/search_field"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_marginStart="15dp"
            android:layout_marginTop="33dp"
            android:background="@drawable/search_layout"
            android:ems="10"
            android:hint="Chercher içi"
            android:inputType="textPersonName"
            android:paddingBottom="10dp"
            android:paddingLeft="20dp"
            android:paddingRight="20dp"
            android:paddingTop="10dp"
            android:textColor="#999999"
            android:textSize="16sp" />

        <Button
            android:id="@+id/search_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentEnd="true"
            android:layout_alignTop="@+id/search_field"
            android:layout_marginEnd="60dp"
            android:text="Ajouter" />
    </RelativeLayout>

    <ListView
        android:id="@+id/contactframe"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="20dp"
        android:layout_marginRight="16dp"
        android:scrollbarSize="4dp"
        android:scrollbarThumbVertical="@drawable/scrollbar"
        android:scrollbars="vertical"
        tools:context="com.android.pfe.fragment.ContactFragment"></ListView>
</LinearLayout>

Answer 1

您已使用 addListenerForSingleValueEvent 一次获取数据并且不保持底层连接打开以监听 firebase 端的任何数据更改。

您只需使用 addValueEventListener 而不是 addListenerForSingleValueEvent ，如下所示。

mDatabase = FirebaseDatabase.getInstance().getReference("User").child(auth.getCurrentUser().getUid().toString())
            .child("contact");

// This is where you should use the addValueEventListener instead of addListenerForSingleValueEvent
mDatabase.addValueEventListener(valueEventListener);

我正在从 firebase documentation 复制对这里有用的部分.

In some cases you may want a callback to be called once and then immediately removed, such as when initializing a UI element that you don't expect to change. You can use the addListenerForSingleValueEvent() method to simplify this scenario: it triggers once and then does not trigger again.

希望这能解决您的问题。