使用回收视图从 Firebase 获取片段数据

Question

我正在尝试从片段中的回收视图中的Firebase获取数据，但是当我这样做时，它不会显示任何内容，但是当我但是在活动中回收视图时，它可以工作，那么有什么问题？

• 我已经阅读了许多像我自己的问题，但我没有找到解决方案，为什么回收视图没有显示任何内容，当我将其投入活动时，它可以毫无问题地工作？

片段

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.tab1, container, false);

final FragmentActivity c = getActivity();
rv = view.findViewById(R.id.rv);
rv.setLayoutManager(new LinearLayoutManager(c));

db= FirebaseDatabase.getInstance().getReference();
helper=new FirebaseHelper(db);
adapter=new MyAdapter(c,helper.retrieve());
rv.setAdapter(adapter);
Toast.makeText(c,"done",Toast.LENGTH_LONG).show();
return inflater.inflate(R.layout.tab1, container, false);
}
}

FirbaseHelper

public class FirebaseHelper {
DatabaseReference db;
Boolean saved=null;
ArrayList<Spacecraft> spacecrafts=new ArrayList<>();
public FirebaseHelper(DatabaseReference db) {
this.db = db;
}
//WRITE IF NOT NULL
public Boolean save(Spacecraft spacecraft)
{
if(spacecraft==null)
{
saved=false;
}else
{
try
{
db.child("Spacecraft").push().setValue(spacecraft);
saved=true;
}catch (DatabaseException e)
{
e.printStackTrace();
saved=false;
}
}
return saved;
}
//IMPLEMENT FETCH DATA AND FILL ARRAYLIST
private void fetchData(DataSnapshot dataSnapshot)
{
spacecrafts.clear();
for (DataSnapshot ds : dataSnapshot.getChildren())
{
Spacecraft spacecraft=ds.getValue(Spacecraft.class);
spacecrafts.add(spacecraft);
}
}
//READ THEN RETURN ARRAYLIST
public ArrayList<Spacecraft> retrieve() {
db.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
fetchData(dataSnapshot);


}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
fetchData(dataSnapshot);
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
return spacecrafts;
}
}

阿达布特

public class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
Context c;
ArrayList<Spacecraft> spacecrafts;
public MyAdapter(Context c, ArrayList<Spacecraft> spacecrafts) {
this.c = c;
this.spacecrafts = spacecrafts;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v=LayoutInflater.from(c).inflate(R.layout.model,parent,false);
return new MyViewHolder(v);
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
final  Spacecraft s=spacecrafts.get(position);
holder.nameTxt.setText(s.getName());
holder.propTxt.setText(s.getPropellant());
holder.descTxt.setText(s.getDescription());
holder.setItemClickListener(new ItemClickListener() {
@Override
public void onItemClick(int pos) {
//OPEN DETAI ACTIVITY
openDetailActivity(s.getName(),s.getDescription(),s.getPropellant());
}
});
}
@Override
public int getItemCount() {
return spacecrafts.size();
}
//OPEN DETAIL ACTIVITY
private void openDetailActivity(String...details)
{
Intent i=new Intent(c,DetailActivity.class);
i.putExtra("NAME_KEY",details[0]);
i.putExtra("DESC_KEY",details[1]);
i.putExtra("PROP_KEY",details[2]);
c.startActivity(i);
}
}

太空船

public class Spacecraft {
String name,propellant,description;
public Spacecraft() {
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPropellant() {
return propellant;
}
public void setPropellant(String propellant) {
this.propellant = propellant;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
}

Answer 1

将适配器设置为回收器视图后，在片段中再添加一行代码。

adapter.notifyDataSetChanged();

您忘记在获取数据后通知适配器。

adapter=new MyAdapter(c,helper.retrieve());
rv.setAdapter(adapter);
adapter.notifyDataSetChanged();