java试图调用虚拟方法“void 安卓x”。回收视图。小装置。回收视图。空对象引用上的setHasFixedSize（布尔）“”

1 周，3 日 Questions & Answers 1226

因此，基本上当我运行我的应用程序时，该应用程序不会给我任何错误。但是，当我尝试在我的应用程序中打开一个名为“查找食物捐赠”的页面时，它在日志中给了我以下错误代码：

'Attempt to invoke virtual method 'void 安卓x.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference' and also said that its Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void 安卓x.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference:

在com。实例多年发展目标项目。发现食物的国家。onCreate（findfooddonions.java:66）

下面是Java文件中发生错误的应用程序的代码（粗体）

public class FindFoodDonations extends AppCompatActivity{
    private DatabaseReference ProductsRef;
    private RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;

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

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

        BottomNavigationView bottomNavigationView = findViewById(R.id.bottom_organization_navigation);
        bottomNavigationView.setSelectedItemId(R.id.nav_find_donations);
        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.nav_find_donations:
                        return true;
                    case R.id.nav_organization_home:
                        startActivity(new Intent(getApplicationContext()
                                , HomeOrganization.class));
                        overridePendingTransition(0, 0);
                        return true;
                    case R.id.nav_organization_logout:
                        FirebaseAuth.getInstance().signOut();
                        Intent intosignup = new Intent(FindFoodDonations.this, MainActivity.class);
                        startActivity(intosignup);
                        return true;
                }
                return false;
            }
        });
        recyclerView = findViewById(R.id.recycler_menu);
        **recyclerView.setHasFixedSize(true);**
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

    }

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

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


        FirebaseRecyclerAdapter<Product, ProductViewHolder> adapter =
                new FirebaseRecyclerAdapter<Product, ProductViewHolder>(options) {
                    @Override
                    protected void onBindViewHolder(@NonNull ProductViewHolder productViewHolder, int i, @NonNull Product product) {
                        productViewHolder.txtProductName.setText(product.getPname());
                        productViewHolder.txtProductPrice.setText("Quantity = " + product.getQuantity() + " KG's");
                        Picasso.get().load(product.getImage()).into(productViewHolder.imageView);
                    }

                    @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();
    }
}

上面页面的XML文件的代码为：

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
    xmlns:app="http://schemas.安卓.com/apk/res-auto"
    xmlns:tools="http://schemas.安卓.com/tools"
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent"
    tools:context=".FindFoodDonations">
    <com.google.安卓.material.bottomnavigation.BottomNavigationView
        安卓:layout_width="match_parent"
        安卓:layout_height="wrap_content"
        安卓:id="@+id/bottom_organization_navigation"
        app:itemBackground="@color/design_default_color_on_primary"
        app:itemTextColor="@drawable/selector"
        app:itemIconTint="@drawable/selector"
        app:menu="@menu/organizationbottom_navigation"
        安卓:layout_alignParentBottom="true"/>

还有一个链接的页面（我不知道是否有必要，但我会把它放在这里）

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
    xmlns:app="http://schemas.安卓.com/apk/res-auto"
    xmlns:tools="http://schemas.安卓.com/tools"
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".HomeActivity">

    <安卓.support.v7.widget.RecyclerView
        安卓:id="@+id/recycler_menu"
        安卓:layout_width="match_parent"
        安卓:layout_height="match_parent"
        安卓:scrollbars="vertical"
        >
    </安卓.support.v7.widget.RecyclerView>

</RelativeLayout>

我以前没有遇到过这样的错误，所以我不知道该怎么办

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java试图调用虚拟方法“void 安卓x”。回收视图。小装置。回收视图。空对象引用上的setHasFixedSize（布尔）“”

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