Firebase 同步方法未同步

Question

Code

public class HomeScreen_Friends extends Fragment {
private View rootView;
private String userName;
private String UID;
private TextView noUsersText;
private ProgressDialog mProgressDialogue;
private FirebaseAuth mAuth;
private FirebaseUser currentUser;
private  DatabaseReference mDatabaseReference;
private  DatabaseReference mUsersDatabase;
private RecyclerView mUsersList;
private FirebaseRecyclerAdapter<AllUsersHelper, UsersViewHolder> firebaseRecyclerAdapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_friends, container, false);
noUsersText = (TextView) rootView.findViewById(R.id.noUsersText);
mUsersList = (RecyclerView) rootView.findViewById(R.id.usersList);
mUsersList.addItemDecoration(new DividerItemDecoration(getContext(),
DividerItemDecoration.HORIZONTAL));

mAuth = FirebaseAuth.getInstance();
currentUser = mAuth.getCurrentUser();
UID = mAuth.getCurrentUser().getUid();
mDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Friends").child(UID);
mDatabaseReference.keepSynced(true);
mUsersDatabase = FirebaseDatabase.getInstance().getReference().child("UserData");
mUsersDatabase.keepSynced(true);
mProgressDialogue = new ProgressDialog(getActivity());
mProgressDialogue.setMessage("Loading...");
mProgressDialogue.show();
mUsersList.setLayoutManager(new LinearLayoutManager(getActivity()));
FirebaseRecyclerOptions<AllUsersHelper> options =
new FirebaseRecyclerOptions.Builder<AllUsersHelper>()
.setQuery(mDatabaseReference, AllUsersHelper.class)
.build();
firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<AllUsersHelper, UsersViewHolder>(options) {
@Override
protected void onBindViewHolder(@NonNull final UsersViewHolder holder, int position, @NonNull AllUsersHelper model) {
holder.setName(model.getName());
holder.setStatus(model.getStatus());
holder.setImage(model.getImage());
final String userId = getRef(position).getKey();
mUsersDatabase.orderByChild("Name");
mUsersDatabase.child(userId).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String mName = dataSnapshot.child("Name").getValue().toString();
String mStatus = dataSnapshot.child("Status").getValue().toString();
String mDisplayImage = dataSnapshot.child("Image").getValue().toString();
if(dataSnapshot.hasChild("Online")) {
String userOnline = dataSnapshot.child("Online").getValue().toString();
holder.setUserOnline(userOnline);
}
holder.setName(mName);
holder.setImage(mDisplayImage);
holder.setStatus(mStatus);
mProgressDialogue.dismiss();
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});

holder.mView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference().child("UserData").child(userId);
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
userName = dataSnapshot.child("Name").getValue().toString();
Intent intent = new Intent(getActivity(), Chat.class);
intent.putExtra("Recievers_Id", userId);
intent.putExtra("Recievers_Name", userName);
startActivity(intent);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});
}


@Override
public UsersViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.custom_activity_all_users, parent, false);
return new UsersViewHolder(view);
}
};
mUsersList.setAdapter(firebaseRecyclerAdapter);
return rootView;
}
public static class UsersViewHolder extends RecyclerView.ViewHolder {
public View mView;
public UsersViewHolder(View itemView) {
super(itemView);
mView = itemView;
}
public void setName(String name) {
TextView mDisplayName = (TextView) mView.findViewById(R.id.display_name);
mDisplayName.setText(name);
}
public void setStatus(String status) {
TextView mDisplayStatus = (TextView) mView.findViewById(R.id.display_status);
mDisplayStatus.setText(status);
}
public void setImage(String image) {
CircularImageView mDisplayImage = (CircularImageView) mView.findViewById(R.id.circleImageView);
Picasso.get().load(image).into(mDisplayImage);
}
public void setUserOnline(String userOnline) {
ImageView userOnlineView = (ImageView) mView.findViewById(R.id.online);
if(userOnline.equals("Online")){
userOnlineView.setVisibility(View.VISIBLE);
} else {
userOnlineView.setVisibility(View.INVISIBLE);
}
}
}
@Override
public void onStart() {
super.onStart();
firebaseRecyclerAdapter.startListening();
}
@Override
public void onStop() {
super.onStop();
if(firebaseRecyclerAdapter != null) {
firebaseRecyclerAdapter.stopListening();
}
}
}

我应该在哪里放置 keepSynced 方法以离线检索数据，因为我在数据库引用下方尝试过，当我没有互联网时它仍然不显示我的数据。有人可以帮我吗...此外，如果 resukt 为空，我如何停止进度对话框并显示一个文本，说明没有用户。

Answer 1

现在你只是告诉Firebase在你的Friends和UserData节点上保持一个空侦听器处于活动状态。这可确保来自这些节点的数据始终保持最新(即使您没有附加任何其他侦听器(，但数据仍仅保留在内存中。

若要将内存缓存保存到磁盘，以便在启动应用时没有互联网连接时可以重新加载它，你需要在应用启动时调用FirebaseDatabase.getInstance().setPersistenceEnabled(true)。请参阅在 Firebase 文档中启用磁盘持久性。

另请参阅：

• Firebase ： setPersistenceEnabled 和 keepSynced 有什么区别？