Question

错误消息：（-原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void androidx.recyclerview.widget.RecyclerView.setHasFixedSize（boolean）'）

访问此RecyclerView时，应用程序崩溃：

    if (!type.equals("Admin"))
    {
        userNameTextView.setText(Prevalent.currentOnlineUser.getName());
        Picasso.get().load(Prevalent.currentOnlineUser.getImage()).placeholder(R.drawable.profile).into(profileImageView);
    }


    recyclerView = (RecyclerView) findViewById(R.id.recycler_menu);
    recyclerView.setHasFixedSize(true);
    layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
}

这是RecyclerView：

<androidx.recyclerview.widget.RecyclerView
  android:id="@+id/recycler_menu"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:scrollbars="vertical"/>

Java类：

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




    recyclerView = (RecyclerView) findViewById(R.id.recycler_menu) ;


    Intent intent = getIntent();
    Bundle bundle = intent.getExtras();
    if (bundle != null)
    {
        type = getIntent().getExtras().get("Admin").toString();
    }



    ProductsRef = FirebaseDatabase.getInstance().getReference().child("Products");


    Paper.init(this);


    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    toolbar.setTitle("Home");
    setSupportActionBar(toolbar);


    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view)
        {
            if (!type.equals("Admin"))
            {
                Intent intent = new Intent(HomeActivity.this, CartActivity.class);
                startActivity(intent);
            }
        }
    });


    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.addDrawerListener(toggle);
    toggle.syncState();


    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    View headerView = navigationView.getHeaderView(0);
    TextView userNameTextView = headerView.findViewById(R.id.user_profile_name);
    CircleImageView profileImageView = headerView.findViewById(R.id.user_profile_image);


    if (!type.equals("Admin"))
    {
        userNameTextView.setText(Prevalent.currentOnlineUser.getName());
        Picasso.get().load(Prevalent.currentOnlineUser.getImage()).placeholder(R.drawable.profile).into(profileImageView);
    }


    recyclerView = (RecyclerView) findViewById(R.id.recycler_menu);
    recyclerView.setHasFixedSize(true);
    layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
}


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

    FirebaseRecyclerOptions<Products> options =
            new FirebaseRecyclerOptions.Builder<Products>()
                    .setQuery(ProductsRef, Products.class)
                    .build();


    FirebaseRecyclerAdapter<Products, ProductViewHolder> adapter =
            new FirebaseRecyclerAdapter<Products, ProductViewHolder>(options) {
                @Override
                protected void onBindViewHolder(@NonNull ProductViewHolder holder, int position, @NonNull final Products model)
                {
                    holder.txtProductName.setText(model.getPname());
                    holder.txtProductDescription.setText(model.getDescription());
                    holder.txtProductPrice.setText("Price = " + model.getPrice() + "$");
                    Picasso.get().load(model.getImage()).into(holder.imageView);


                    holder.itemView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view)
                        {
                            if (type.equals("Admin"))
                            {
                                Intent intent = new Intent(HomeActivity.this, AdminMaintainProductsActivity.class);
                                intent.putExtra("pid", model.getPid());
                                startActivity(intent);
                            }
                            else
                            {
                                Intent intent = new Intent(HomeActivity.this, ProductDetailsActivity.class);
                                intent.putExtra("pid", model.getPid());
                                startActivity(intent);
                            }
                        }
                    });
                }

                @NonNull
                @Override
                public ProductViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
                {
                    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.product_items_layout, parent, false);
                    ProductViewHolder holder = new ProductViewHolder(view);
                    return holder;
                }
            };
    recyclerView.setAdapter(adapter);
    adapter.startListening();
}

Answer 1

我可以看到您的代码没有问题。所以我认为您在setContentView()

中放置了错误的布局

或者，如果不是这种情况，只需确保布局中确实存在一个带有指定ID的RecyclerView。

如果确定，只需再invalidate cache & restart和build

访问RecyclerView时，应用程序崩溃

1 个答案: