java - 订单 Activity 因空点引用而崩溃

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 5 年前。

我制作了订单食品应用程序。当我单击订单 Activity 应用程序时，应用程序崩溃并在下面的 OrderStatus.java 中给出三个错误，即 logcat 和 OrderStatus actitvity。单击图标后需要显示订单状态。

Logcat 错误

    java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.hashCode()' on a null object reference
        at com.example.sharma.digimenuserver.Common.Common.convertCodeToStatus(Common.java:16)
        at com.example.sharma.digimenuserver.OrderStatus$1.onBindViewHolder(OrderStatus.java:78)
        at com.example.sharma.digimenuserver.OrderStatus$1.onBindViewHolder(OrderStatus.java:64)
        at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:122)
        at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6673)
        at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6714)
        at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5647)
        at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5913)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5752)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5748)
        at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2232)
        at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1559)
        at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1519)
        at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:614)
        at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3812)
        at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3529)
        at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1767)
        at android.support.v7.widget.RecyclerView$1.run(RecyclerView.java:356)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:549)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5292)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
07-22 17:30:08.181 3099-3109/com.example.sharma.digimenuserver I/art: Debugger is no longer active
07-22 17:34:22.748 3099-3141/com.example.sharma.digimenuserver I/FirebaseAuth: [FirebaseAuth:] Loading module via 

OrderStatus.java

公共(public)类 OrderStatus 扩展 AppCompatActivity {

RecyclerView recyclerView;
RecyclerView.LayoutManager layoutManager;

FirebaseRecyclerAdapter<Request,OrderViewHolder> adapter;

FirebaseDatabase db;
DatabaseReference requests;

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

    db = FirebaseDatabase.getInstance();
    requests=db.getReference("Requests");

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



        loadOrders();

}

private void loadOrders() {


    FirebaseRecyclerOptions<Request> options =
            new FirebaseRecyclerOptions.Builder<Request>()
           .setQuery(requests, Request.class).build();

    adapter = new FirebaseRecyclerAdapter<Request, OrderViewHolder>(options) {
        @NonNull
        @Override
        public OrderViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

            View view = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.order_layout, parent, false);
            return new OrderViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull OrderViewHolder holder, int position, @NonNull Request model) {
            //do binding stuff
            holder.txtOrderId.setText(adapter.getRef(position).getKey());
            holder.txtOrderStatus.setText(Common.convertCodeToStatus(model.getStatus()));
            holder.txtOrderAddress.setText(model.getAddress());
            holder.txtOrderPhone.setText(model.getPhone());
            holder.setItemClickListener(new ItemClickListener() {
                @Override
                public void onClick(View view, int position, boolean isLongClick) {

                }
            });
        }
    };
    adapter.notifyDataSetChanged();

    recyclerView.setAdapter(adapter);

    adapter.startListening();

}

@Override
public boolean onContextItemSelected(MenuItem item) {

    if(item.getTitle().equals(Common.UPDATE))
        showUpdateDialog(adapter.getRef(item.getOrder()).getKey(),adapter.getItem(item.getOrder()));
    else  if(item.getTitle().equals(Common.DELETE))
        deleteOrder(adapter.getRef(item.getOrder()).getKey());


    return super.onContextItemSelected(item);
}

private void deleteOrder(String key) {
    requests.child(key).removeValue();

}

private void showUpdateDialog(String key, final Request item) {

    final AlertDialog.Builder alertDialog = new AlertDialog.Builder(OrderStatus.this);
    alertDialog.setTitle("Update Order");
    alertDialog.setMessage("Please Choose Status");

    LayoutInflater inflater = this.getLayoutInflater();
    final View view = inflater.inflate(R.layout.update_order_layout,null);

    spinnner = (MaterialSpinner)findViewById(R.id.statusSpinner);
    spinnner.setItems("Placed","On my way","Shipped");
    alertDialog.setView(view);

    final String localKey = key;
    alertDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {

            dialog.dismiss();
            item.setStatus(String.valueOf(spinnner.getSelectedIndex()));
            requests.child(localKey).setValue(item);
        }
    });

    alertDialog.setNegativeButton("NO", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.dismiss();
        }
    });

    alertDialog.show();



}

}

**在三行内得到错误**

        switch (code) {
            case "0":
                return "Placed";
            case "1":
                return "On my way";
            default:
                return "Shipped";
        }

     holder.txtOrderStatus.setText(Common.convertCodeToStatus(model.getStatus()));
 adapter = new FirebaseRecyclerAdapter<Request, OrderViewHolder>(options) {



https://send.firefox.com/download/80a23ccfae/#W_ricyMLLaYtPkPg_UGNFA

Answer 1

您没有提及哪一行，但我最好的猜测是 code is null 可能会检查这一点。Java 使用 .equals() 和 .hashCode() 来验证 switch 语句中的字符串，因此如果 code 为 null，您将收到此错误