java - 我正在从 Firebase 拍摄数据，但无法将其添加到列表中

Question

我实际上获取了数据并用 print 打印了它。但是当我添加到列表中时，它给出了空对象异常。我该如何解决这个问题？我收到错误，因为我正在创建一个空对象。我不明白为什么。,我该怎么做才能解决？

    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot ds : dataSnapshot.getChildren()){
                Mac mac = new Mac();
                mac.setMackodu(ds.getValue(Mac.class).getMackodu());
                mac.setTakimlar(ds.getValue(Mac.class).getTakimlar());
                mac.setTahmin(ds.getValue(Mac.class).getTahmin());
                System.out.println("macss " + mac.getMackodu());
                System.out.println("macss " + mac.getTakimlar());
                System.out.println("macss " + mac.getTahmin());
                macList.add(mac);

            }

            myRecyclerAdapter = new MyRecyclerAdapter(getContext(),macList);
            recyclerView.setAdapter(myRecyclerAdapter);
            myRecyclerAdapter.notifyDataSetChanged();

        }

public class Mac{

    private String macKodu;
    private String takimlar;
    private String tahmin;

    public Mac() {
    }

    public Mac(String macKodu, String takimlar, String tahmin) {
        this.macKodu = macKodu;
        this.takimlar = takimlar;
        this.tahmin = tahmin;
    }

    public String getMacKodu() {
        return macKodu;
    }

    public void setMacKodu(String macKodu) {
        this.macKodu = macKodu;
    }

    public String getTakimlar() {
        return takimlar;
    }

    public void setTakimlar(String takimlar) {
        this.takimlar = takimlar;
    }

    public String getTahmin() {
        return tahmin;
    }

    public void setTahmin(String tahmin) {
        this.tahmin = tahmin;
    }

Answer 1

放入这两行

myRecyclerAdapter = new MyRecyclerAdapter(getContext(),macList);
recyclerView.setAdapter(myRecyclerAdapter); 

出

myRef.addValueEventListener