java - FirebaseRecyclerAdapter 抛出空对象

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 4 年前。

我的应用程序在登录后立即崩溃，并且在

上给出了一个 null 对象

adapter = new FirebaseRecyclerAdapter<Category, MenuViewHolder>(Category.class, R.layout.menu_item, MenuViewHolder.class, category)

有人可以帮忙或者有更好的主意吗？

private void LoadMenu(){
        adapter = new FirebaseRecyclerAdapter<Category, MenuViewHolder>(Category.class, R.layout.menu_item, MenuViewHolder.class, category) {
            @Override
            protected void populateViewHolder(MenuViewHolder viewHolder, Category model, int position) {
                viewHolder.txtMenuName.setText(model.getName());
                Picasso.get().load(model.getImage()).into(viewHolder.imageView);
                final Category clickItem = model;
                viewHolder.setItemClickListener(new ItemClickListener() {
                    @Override
                    public void onClick(View v, int position, boolean isLongClick) {
                        //Get CategoryId and send to new Activity
                        Intent foodList = new Intent(Home.this, FoodList.class);
                        //Because Category is key, so we just get the key of this item
                        foodList.putExtra("CategoryId", adapter.getRef(position).getKey());
                        startActivity(foodList);
                    }
                });
            }
        };
        recycler_menu.setAdapter(adapter);
    }

这是导致我的应用程序崩溃的完整堆栈跟踪错误，我不知道为什么，我启动了 FireDatabase 并将数据库引用设置为我的 firedatabase 中的“类别”

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.fahad.foodie, PID: 4287
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.fahad.foodie.Home$2.populateViewHolder(Home.java:88)
        at com.fahad.foodie.Home$2.populateViewHolder(Home.java:85)
        at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:184)
        at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6781)
        at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6823)
        at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5752)
        at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6019)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5858)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5854)
        at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2230)
        at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1557)
        at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1517)
        at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:612)
        at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3924)
        at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3641)
        at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1888)
        at android.support.v7.widget.RecyclerView$1.run(RecyclerView.java:407)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
        at android.view.Choreographer.doCallbacks(Choreographer.java:761)
        at android.view.Choreographer.doFrame(Choreographer.java:693)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:6981)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1445)

Answer 1

您的 TextView 未正确定义。

根据 logcat 消息，

viewHolder.txtMenuName 为 NULL。

请在您的 MenuViewHolder 中正确定义它，如下所示，

 public MenuViewHolder(View itemView) {
        super(itemView);

        txtMenuName = itemView.findViewById(R.id.menu_name);
        imageMenu = itemView.findViewById(R.id.menu_image);

        itemView.setOnClickListener(this);
    }

您必须确保txtMenuName正确映射到中的textview id(例如android:id="@+id/menu_name") menu_item.xml.