未连接适配器；跳过布局：RecyclerView & Adapter

Question

我已经看到很多关于这个问题的答案，但对我的编码没有任何帮助。

我参考了基于此youtube 视频的代码，现在我遇到了这个问题。不知道他的代码是如何工作的，而我的不是。显然我也是这个话题的新手（RecyclerView）。

这是我的主要活动：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view_product)  ;

    ref = FirebaseDatabase.getInstance().getReference().child("buddymealplanneruser").child("Products");
    recyclerView = findViewById(R.id.stallproductRecyclerView);

    //newest
    LinearLayoutManager manager = new LinearLayoutManager(this);
    manager.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(manager);
    recyclerView.setHasFixedSize(true);
    //
    searchView = findViewById(R.id.searchProductStall);

}

@Override
protected void onRestart() {
    super.onRestart();
    if (ref!=null)
    {
         ref.addValueEventListener(new ValueEventListener() {
             @Override
             public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                 if (dataSnapshot.exists())
                 {
                     list = new ArrayList<>();
                     for(DataSnapshot ds : dataSnapshot.getChildren())
                     {

                         list.add(ds.getValue(Model.class));
                     }
                     ViewHolder viewHolder = new ViewHolder(list);
                     recyclerView.setAdapter(viewHolder);
                 }

             }

             @Override
             public void onCancelled(@NonNull DatabaseError databaseError) {
                 Toast.makeText(ViewProduct.this, databaseError.getMessage(),
                         Toast.LENGTH_SHORT).show();
             }
         });
    }

这是 ViewHolder 类。

ArrayList<Model> list;
    public ViewHolder (ArrayList<Model> list)
    {
        this.list=list;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {

        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_product,
                viewGroup,false);


        return new MyViewHolder(view);


    }

Answer 1

在oncreate() 中使用空的data 设置适配器，在fetching 数据之后，您应该调用adapter.notifyDataSetChanged()，如下所示。

ViewHolder viewHolder;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view_product)  ;

    ref = FirebaseDatabase.getInstance().getReference().child("buddymealplanneruser").child("Products");
    recyclerView = findViewById(R.id.stallproductRecyclerView);

    //newest
    LinearLayoutManager manager = new LinearLayoutManager(this);
    manager.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(manager);
    recyclerView.setHasFixedSize(true);
    //
    searchView = findViewById(R.id.searchProductStall);

    // here you have to set the adapter to your recycler view
    list = new ArrayList<>();
    viewHolder = new ViewHolder(list);
    recyclerView.setAdapter(viewHolder);

}

@Override
protected void onRestart() {
    super.onRestart();
    if (ref!=null)
    {
         ref.addValueEventListener(new ValueEventListener() {
             @Override
             public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                 if (dataSnapshot.exists())
                 {
                     // clear your previous data
                     list.clear();
                     for(DataSnapshot ds : dataSnapshot.getChildren())
                     {
                         list.add(ds.getValue(Model.class));
                     }
                     // here you have to notify you adapter that your data set is changed like below
                     viewHolder.notifyDataSetChanged();
                 }

             }

             @Override
             public void onCancelled(@NonNull DatabaseError databaseError) {
                 Toast.makeText(ViewProduct.this, databaseError.getMessage(),
                         Toast.LENGTH_SHORT).show();
             }
         });
    }