Question

我已尝试过所有内容，但是当我打开应用程序时，我的firebase数据没有自动加载，我必须单击一个edittext来加载数据。

我试过了

  adapter.Update(data);
  recycler.invalidate();
  notifyDataSetChanged();
  adapter.notifyDataSetChanged();

请有人帮助我。

编辑：

我正在这样保存到firebase：

    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);
            }
        });
        return spacecrafts;
    }
}

我的观看者类

public MyViewHolder(View itemView) {
        super(itemView);
        nameTxt= (TextView) itemView.findViewById(R.id.nameTxt);
        propTxt= (TextView) itemView.findViewById(R.id.propellantTxt);
        descTxt= (TextView) itemView.findViewById(R.id.descTxt);
        itemView.setOnClickListener(this);
    }
    public void setItemClickListener(ItemClickListener itemClickListener)
    {
        this.itemClickListener=itemClickListener;
    }
    @Override
    public void onClick(View view) {
        this.itemClickListener.onItemClick(this.getLayoutPosition());
    }

我的适配器类

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);
    }

在onCreate中我的主要活动我正在调用这样的数据

recycler = (RecyclerView) rootView.findViewById(R.id.recycler);
recycler.setLayoutManager(new LinearLayoutManager(getActivity()));
database = FirebaseDatabase.getInstance().getReference();
spacecraft = new ArrayList<>();
firebasehelper = new FirebaseHelper(database);
adapter = new JAdapter(getActivity(), firebasehelper.retrieve());
recycler.setAdapter(adapter);

Answer 1

问题在于retrieve方法：它添加了一个ChildEventListener执行异步（意味着它在获取子数据之前不会阻塞）然后它立即返回仍未由异步侦听器代码填充的spacecrafts列表。

您应该在提取数据的实际代码中刷新RecyclerView适配器，例如在fetchData方法中，例如：

private void fetchData(DataSnapshot dataSnapshot)
{
    spacecrafts.clear();
    for (DataSnapshot ds : dataSnapshot.getChildren())
    {
        Spacecraft spacecraft=ds.getValue(Spacecraft.class);
        spacecrafts.add(spacecraft);
    }
    adapter.spacecrafts = spacecrafts; // update the list in the adapter
    adapter.notifyDataSetChanged(); // refresh
}

在这种情况下，retrieve方法可以有void返回类型，因为从中返回列表毫无意义。

Answer 2

使用FirebaseRecyclerAdapter从Firebase加载数据。

Answer 3

将helper constructer修改为：

 public FirebaseHelper(Context c, DatabaseReference db, ListView lv) {
    this.c = c;
    this.db = db;
    this.lv = lv;
}

然后在for循环后将其添加到fetchData方法：

if (spacecrafts.size() > 0)
    {
        adapter = new CustomAdapter(c, spacecrafts);
        lv.setAdapter(adapter);
        adapter.notifyDataSetChanged();
    }

然后在主要活动中修改它：

    helper = new FirebaseHelper(this, db, lv);
    //ADAPTER
    //adapter = new CustomAdapter(this, helper.retrieve());
    //lv.setAdapter(adapter);
    helper.retrieve();

这对你有用。

Recylerview不会自动从firebase Android Studio加载数据

3 个答案: