问题：

当恢复activity时,RecyclerView返回null

计承德

2023-03-14

我有一个RecolyerView，当activity启动时，它工作得很好。当我从那个activity去另一个再回来时，recyclerView是空的。它什么也不显示，但有时它返回值，但布局受到干扰，即项目之间有空隙，或布局将有一个很大的空隙，从activity顶部。

类的代码是：

public class product_page extends AppCompatActivity {

  FirebaseAuth mAuth;
  String s, product;
  ProgressDialog progressDialog;
  private RecyclerView recyclerView;
  FirebaseDatabase firebaseDatabase;
  DatabaseReference databaseReference;
  DatabaseReference db;
  FirebaseRecyclerAdapter<ProductItemsConstructor, productViewHolder> FirebaseAdapter;

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

        Intent intent = getIntent();
        s = intent.getExtras().getString("pos");
        product = intent.getExtras().getString("product");

    mAuth = FirebaseAuth.getInstance();
    firebaseDatabase = FirebaseDatabase.getInstance();
    databaseReference = FirebaseDatabase.getInstance().getReference();

    RecyclerView.LayoutManager layoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
   // RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView = (RecyclerView) findViewById(R.id.recyclerView1);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());


    Query query = firebaseDatabase.getReference().child("Products").child(s).child(product).orderByKey();

    FirebaseRecyclerOptions options = new FirebaseRecyclerOptions.Builder<ProductItemsConstructor>().setQuery(query,ProductItemsConstructor.class).build();

    FirebaseAdapter = new FirebaseRecyclerAdapter<ProductItemsConstructor, productViewHolder>(options) {


        @Override
        public productViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.product_items,parent,false);
            return new productViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull productViewHolder holder, int position, @NonNull ProductItemsConstructor model) {
            holder.Heading(model.getHeading());
            holder.Price(model.getPrice());
            holder.Prates(model.getPprice());
            holder.Rating(model.getRating());
            holder.setImg(getApplicationContext(),model.getImageUrl());
        }
    };
    recyclerView.setAdapter(FirebaseAdapter);

}


@Override
protected void onStart() {
    super.onStart();

    FirebaseAdapter.startListening();
    recyclerView.setAdapter(FirebaseAdapter);
}

@Override
protected void onStop() {
    super.onStop();
    FirebaseAdapter.stopListening();
}

@Override
protected void onResume() {
    super.onResume();

    FirebaseAdapter.notifyDataSetChanged();
}

@Override
public void onBackPressed() {
    super.onBackPressed();
    Intent in = new Intent(product_page.this, MainActivity.class);
    startActivity(in);
}

public class productViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    TextView head, rate, Prate, rating;
    ImageView img;


    public productViewHolder(final View itemView) {
        super(itemView);
        itemView.setOnClickListener(this);
    }

    private void Heading(String heading) {
        head = (TextView) itemView.findViewById(R.id.Pheading);
        head.setText(heading);
    }

    private void Price(String price) {
        rate = (TextView) itemView.findViewById(R.id.Pprice);
        rate.setText(price);
    }

    private void Prates(String prate){
        Prate = (TextView)itemView.findViewById(R.id.pRate);
        Prate.setText(prate);
    }

    private void Rating(String rting){
        rating = (TextView)itemView.findViewById(R.id.Rating);
        rating.setText(rting);
    }

    private void setImg(Context ctx, String img1) {
        img = (ImageView) itemView.findViewById(R.id.PImage);
        Picasso.with(ctx).load(img1).placeholder(R.drawable.notification).into(img);
        // progressDialog.dismiss();
    }
}

这是activity首先启动时的影像

在此输入图像说明

这是恢复activity时的形象

在此输入图像说明

日志如下所示

null

如有任何帮助或帮助，我们将不胜感激。

共有2个答案

许庆

2023-03-14

只对onResume（）方法进行这些更改。

@Override
protected void onResume() {
super.onResume();

   //FirebaseAdapter.notifyDataSetChanged();
   getData();
   }
}
private void getData() {
    RecyclerView.LayoutManager layoutManager = new StaggeredGridLayoutManager(2, android.support.v7.widget.StaggeredGridLayoutManager.VERTICAL);
    // RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView = (android.support.v7.widget.RecyclerView) findViewById(R.id.recyclerView1);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setItemAnimator(new android.support.v7.widget.DefaultItemAnimator());

    Query query = firebaseDatabase.getReference().child("Products").child(s).child(product).orderByKey();

    FirebaseRecyclerOptions options = new FirebaseRecyclerOptions.Builder<ProductItemsConstructor>().setQuery(query, ProductItemsConstructor.class).build();

    FirebaseAdapter = new FirebaseRecyclerAdapter<ProductItemsConstructor, productViewHolder>(options) {

        @Override
        public productViewHolder onCreateViewHolder(android.view.ViewGroup parent, int viewType) {
            View view = android.view.LayoutInflater.from(parent.getContext()).inflate(R.layout.product_items, parent, false);
            return new productViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@android.support.annotation.NonNull productViewHolder holder, int position, @android.support.annotation.NonNull ProductItemsConstructor model) {
            holder.Heading(model.getHeading());
            holder.Price(model.getPrice());
            holder.Prates(model.getPprice());
            holder.Rating(model.getRating());
            holder.setImg(getApplicationContext(), model.getImageUrl());
        }
    };
    recyclerView.setAdapter(FirebaseAdapter);
    FirebaseAdapter.notifyDataSetChanged();
}

邵飞宇

2023-03-14

请尝试使用以下代码：

public class product_page extends AppCompatActivity {


FirebaseAuth mAuth;
String s, product;
ProgressDialog progressDialog;
private RecyclerView recyclerView;
FirebaseDatabase firebaseDatabase;
DatabaseReference databaseReference;
DatabaseReference db;
FirebaseRecyclerAdapter<ProductItemsConstructor, productViewHolder> FirebaseAdapter;

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

        Intent intent = getIntent();
        s = intent.getExtras().getString("pos");
        product = intent.getExtras().getString("product");

    mAuth = FirebaseAuth.getInstance();
    firebaseDatabase = FirebaseDatabase.getInstance();
    databaseReference = FirebaseDatabase.getInstance().getReference();

    RecyclerView.LayoutManager layoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
   // RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView = (RecyclerView) findViewById(R.id.recyclerView1);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());


    Query query = firebaseDatabase.getReference().child("Products").child(s).child(product).orderByKey();

    FirebaseRecyclerOptions options = new FirebaseRecyclerOptions.Builder<ProductItemsConstructor>().setQuery(query,ProductItemsConstructor.class).build();

    FirebaseAdapter = new FirebaseRecyclerAdapter<ProductItemsConstructor, productViewHolder>(options) {


        @Override
        public productViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.product_items,parent,false);
            return new productViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull productViewHolder holder, int position, @NonNull ProductItemsConstructor model) {
            holder.Heading(model.getHeading());
            holder.Price(model.getPrice());
            holder.Prates(model.getPprice());
            holder.Rating(model.getRating());
            holder.setImg(getApplicationContext(),model.getImageUrl());
        }
    };
    recyclerView.setAdapter(FirebaseAdapter);

}


@Override
protected void onStart() {
    super.onStart();

    FirebaseAdapter.startListening();
    recyclerView.setAdapter(FirebaseAdapter);
}

@Override
protected void onDestroy() {
    FirebaseAdapter.stopListening();
    super.onDestroy();
}

@Override
protected void onResume() {
    super.onResume();

    FirebaseAdapter.notifyDataSetChanged();
}

@Override
public void onBackPressed() {
    super.onBackPressed();
    Intent in = new Intent(product_page.this, MainActivity.class);
    startActivity(in);
}

public class productViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    TextView head, rate, Prate, rating;
    ImageView img;


    public productViewHolder(final View itemView) {
        super(itemView);
        itemView.setOnClickListener(this);
    }

    private void Heading(String heading) {
        head = (TextView) itemView.findViewById(R.id.Pheading);
        head.setText(heading);
    }

    private void Price(String price) {
        rate = (TextView) itemView.findViewById(R.id.Pprice);
        rate.setText(price);
    }

    private void Prates(String prate){
        Prate = (TextView)itemView.findViewById(R.id.pRate);
        Prate.setText(prate);
    }

    private void Rating(String rting){
        rating = (TextView)itemView.findViewById(R.id.Rating);
        rating.setText(rting);
    }

    private void setImg(Context ctx, String img1) {
        img = (ImageView) itemView.findViewById(R.id.PImage);
        Picasso.with(ctx).load(img1).placeholder(R.drawable.notification).into(img);
        // progressDialog.dismiss();
    }

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当恢复activity时,RecyclerView返回null

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