每次用户将项目添加到 Firebase 中的某个数据库引用时，我都会尝试创建一个实时 RecyclerView。这是我的模型类：
@IgnoreExtraProperties
public class Poll {
private String question;
private String image_URL;
public Poll() {
}
public Poll(String Question, String Image_URL){
this.question = Question;
this.image_URL = Image_URL;
}
public String getQuestion() {
return question;
}
public void setQuestion(String question) {
question = question;
}
public String getImage_URL() {
return image_URL;
}
public void setImage_URL(String image_URL) {
image_URL = image_URL;
}
@Exclude
public Map<String, Object> toMap(){
HashMap<String, Object> result = new HashMap<>();
result.put("question", question);
result.put("image_URL", image_URL);
return result;
}
这是我将数据保存到 Firebase 的类。它实际上正在写入 Firebase，因此我可以确认我的写入正确：
mSubmitPollCreation.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//TODO: Need to check if poll requirements are added, i.e. Question, Answer, ......
//check if image has been loaded first
if (resultImageURL == null){
Toast.makeText(getApplicationContext(),getResources().getString(R.string.no_image_selected),Toast.LENGTH_LONG).show();
return;
}
Poll poll = new Poll(mCreatePollQuestion.getText().toString(), resultImageURL);
Map <String, Object> pollMap = poll.toMap();
String key = mBaseRef.child("Polls").push().getKey();
Map<String, Object> childUpdates = new HashMap<String, Object>();
childUpdates.put("/Polls/" + key, pollMap);
mBaseRef.updateChildren(childUpdates);
Intent toHomeActivity = new Intent(CreateActivity.this, HomeActivity.class);
toHomeActivity.putExtra("viewpager_position", 2);
startActivity(toHomeActivity);
}
});
我希望 recyclerview 在添加项目时在所有设备上实时更新。这是我使用 Firebase UI 库填充 RecyclerView 的片段。当我将数据/写入添加到 Firebase（如前面的代码片段中所列）时，我没有在任何设备上看到任何实时更新：
public class LiveFragment extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
private RecyclerView mRecyclerview;
private DatabaseReference mBaseRef;
private DatabaseReference mPollsRef;
private LinearLayoutManager mLayoutManager;
private FirebaseRecyclerAdapter <Poll, PollHolder> mFireAdapter;
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
public LiveFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment LiveFragment.
*/
// TODO: Rename and change types and number of parameters
public static LiveFragment newInstance(String param1, String param2) {
LiveFragment fragment = new LiveFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
final View v = inflater.inflate(R.layout.fragment_new, container, false);
mRecyclerview = (RecyclerView) v.findViewById(R.id.new_RecyclerView);
mBaseRef = FirebaseDatabase.getInstance().getReference();
mPollsRef = mBaseRef.child("Polls");
if (mRecyclerview != null){
mRecyclerview.setHasFixedSize(true);
}
mLayoutManager = new LinearLayoutManager(getActivity().getApplicationContext());
mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL
);
mRecyclerview.setLayoutManager(mLayoutManager);
return v;
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onStart() {
super.onStart();
mFireAdapter = new FirebaseRecyclerAdapter<Poll, PollHolder>(
Poll.class,
R.layout.latest_item,
PollHolder.class,
mPollsRef
){
@Override
protected void populateViewHolder(PollHolder viewHolder, Poll model, int position) {
viewHolder.mPollQuestion.setText(model.getQuestion());
Picasso.with(getActivity().getApplicationContext())
.load(model.getImage_URL())
.fit()
.into(viewHolder.mPollImage);
Log.v("QUESTION", model.getQuestion());
Log.v("IMAGE", model.getImage_URL());
}
};
mRecyclerview.setAdapter(mFireAdapter);
}
@Override
public void onStop() {
super.onStop();
if (mFireAdapter != null){
mFireAdapter.cleanup();
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
public static class PollHolder extends RecyclerView.ViewHolder {
TextView mPollQuestion;
ImageView mPollImage;
public PollHolder(View itemView) {
super(itemView);
mPollQuestion = (TextView) itemView.findViewById(R.id.latest_item_question);
mPollImage = (ImageView) itemView.findViewById(R.id.pollThumbNailImage);
}
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
编辑：我相信由于某种原因写入 Firebase 的数据为空，因为日志Question and ImageURL不返回任何数据。
