Question

我收到此错误：

试图调用虚拟方法'android.view.Window $ Callback 空对象引用上的android.view.Window.getCallback（）'

public class AdaptadorCarrito extends
    RecyclerView.Adapter<AdaptadorCarrito.ViewHolderCarrito> {

ArrayList<CarritoVo> listaCarrito;
AdaptadorCarrito adapter;
RecyclerView.Adapter madapter;
int i = 1;

public AdaptadorCarrito(ArrayList<CarritoVo> listaCarrito) {
    this.listaCarrito = listaCarrito;
}

@NonNull
@Override
public ViewHolderCarrito onCreateViewHolder(@NonNull final ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_list_carrito, null, false);
    final ViewHolderCarrito myHolder = new ViewHolderCarrito(view);
    final CafeteriaDB cafeteriaDB = new CafeteriaDB(parent.getContext());

    myHolder.item_list_carrito.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            int newPosition = myHolder.getAdapterPosition();
            cafeteriaDB.eliminarProducto(myHolder.etiNombre.getText().toString(), myHolder.etiInfo.getText().toString());
            eliminarProducto(newPosition);
            // i++;
            // Toast.makeText(parent.getContext(),"Producto Eliminado "+i+" eliminado",Toast.LENGTH_SHORT).show();
            CarritoCompras obj = new CarritoCompras();
            TextView tv = obj.getTextView(); //Error Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
            tv.setText(String.valueOf(cafeteriaDB.getTotal()));
        }

    });
    return myHolder;
}

private void eliminarProducto(int position) {
    listaCarrito.remove(position);
    notifyItemRemoved(position);
}

@Override
public void onBindViewHolder(@NonNull ViewHolderCarrito holder, int position) {
    CarritoVo positions = listaCarrito.get(position);
    holder.etiNombre.setText(listaCarrito.get(position).getNombre());
    holder.etiPrecio.setText(String.valueOf(listaCarrito.get(position).getPrecio()));
    holder.etiInfo.setText(listaCarrito.get(position).getInfo());
    holder.etiCantidades.setText(String.valueOf(listaCarrito.get(position).getCantidad()));
    holder.etiFoto.setImageBitmap(positions.getFoto());
}

@Override
public int getItemCount() {
    //return listaCarrito.size();
    return (listaCarrito == null) ? 0 : listaCarrito.size();
}

public class ViewHolderCarrito extends RecyclerView.ViewHolder {

    LinearLayout item_list_carrito;
    TextView etiNombre, etiPrecio, etiInfo, etiCantidades, txtTotalB, txtTotalF;
    ImageView etiFoto;

    public ViewHolderCarrito(@NonNull View itemView) {
        super(itemView);
        item_list_carrito = (LinearLayout) itemView.findViewById(R.id.id_carrito_item);
        etiFoto = (ImageView) itemView.findViewById(R.id.fotoC);
        etiNombre = (TextView) itemView.findViewById(R.id.nombreC);
        etiPrecio = (TextView) itemView.findViewById(R.id.precioC);
        etiInfo = (TextView) itemView.findViewById(R.id.infoC);
        etiCantidades = (TextView) itemView.findViewById(R.id.cantidadC);
    }
}
}

活动

public class CarritoCompras extends AppCompatActivity implements Carrito.OnFragmentInteractionListener{

TextView txtTotalF;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_carrito_compras);
    CafeteriaDB db = new CafeteriaDB(this);

    getTextView();

    txtTotalF = (TextView)findViewById(R.id.totalF);

    txtTotalF.setText(String.valueOf(db.totalFilas()));

}

public TextView getTextView(){
    TextView txtTotalB = (TextView)findViewById(R.id.totalB); //Error Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    return txtTotalB;
}



@Override
public void onFragmentInteraction(Uri uri) {

}
}

Answer 1

您可以按照以下方式做

第1步：

一次加载TextView

  TextView txtTotalB; // declare class level

内部onCreate（）

 txtTotalB = (TextView)findViewById(R.id.totalB);

第2步：

创建方法

public TextView getTextView(){
    return txtTotalB
}

第3步：

在适配器类内部访问如下的活动方法

TextView tv = ((CarritoCompras)context).getTextView();
tv.setText(String.valueOf(cafeteriaDB.getTotal()));   // now here you done

Answer 2

您可以使用Interfaces进行通信。

创建如下所示的界面：

outer_decorator

在适配器类中，创建声明类型为public interface RecyclerItemClickListener { void onItemClick(String text); }的变量，并修改适配器的构造函数以接受“ RecyclerItemClickListener”的实例作为参数。即按如下所示修改您的适配器类：

RecyclerItemClickListener

现在在要实例化public class AdaptadorCarrito extends RecyclerView.Adapter<AdaptadorCarrito.ViewHolderCarrito> { RecyclerItemClickListener recyclerItemClickListener; //Here we are declaring a variable of the created interface ArrayList<CarritoVo> listaCarrito; AdaptadorCarrito adapter; RecyclerView.Adapter madapter; int i = 1; //Modifying the constructor to initialize the above declared listener public AdaptadorCarrito(ArrayList<CarritoVo> listaCarrito, RecyclerItemClickListener listener) { this.listaCarrito = listaCarrito; this.recyclerItemClickListener = listener; } @NonNull @Override public ViewHolderCarrito onCreateViewHolder(@NonNull final ViewGroup parent, int viewType) { View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_list_carrito, null, false); final ViewHolderCarrito myHolder = new ViewHolderCarrito(view); final CafeteriaDB cafeteriaDB = new CafeteriaDB(parent.getContext()); myHolder.item_list_carrito.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { int newPosition = myHolder.getAdapterPosition(); cafeteriaDB.eliminarProducto(myHolder.etiNombre.getText().toString(), myHolder.etiInfo.getText().toString()); eliminarProducto(newPosition); // i++; // Toast.makeText(parent.getContext(),"Producto Eliminado "+i+" eliminado",Toast.LENGTH_SHORT).show(); CarritoCompras obj = new CarritoCompras(); /*TextView tv = obj.getTextView(); //Error Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference tv.setText(String.valueOf(cafeteriaDB.getTotal()));*/ //Here we are passing the test to be displayed in the textview to your activity recyclerItemClickListener.onItemClick(String.valueOf(cafeteriaDB.getTotal())); } }); return myHolder; } private void eliminarProducto(int position) { listaCarrito.remove(position); notifyItemRemoved(position); } @Override public void onBindViewHolder(@NonNull ViewHolderCarrito holder, int position) { CarritoVo positions = listaCarrito.get(position); holder.etiNombre.setText(listaCarrito.get(position).getNombre()); holder.etiPrecio.setText(String.valueOf(listaCarrito.get(position).getPrecio())); holder.etiInfo.setText(listaCarrito.get(position).getInfo()); holder.etiCantidades.setText(String.valueOf(listaCarrito.get(position).getCantidad())); holder.etiFoto.setImageBitmap(positions.getFoto()); } @Override public int getItemCount() { //return listaCarrito.size(); return (listaCarrito == null) ? 0 : listaCarrito.size(); } public class ViewHolderCarrito extends RecyclerView.ViewHolder { LinearLayout item_list_carrito; TextView etiNombre, etiPrecio, etiInfo, etiCantidades, txtTotalB, txtTotalF; ImageView etiFoto; public ViewHolderCarrito(@NonNull View itemView) { super(itemView); item_list_carrito = (LinearLayout) itemView.findViewById(R.id.id_carrito_item); etiFoto = (ImageView) itemView.findViewById(R.id.fotoC); etiNombre = (TextView) itemView.findViewById(R.id.nombreC); etiPrecio = (TextView) itemView.findViewById(R.id.precioC); etiInfo = (TextView) itemView.findViewById(R.id.infoC); etiCantidades = (TextView) itemView.findViewById(R.id.cantidadC); } } }对象的Activity中，需要将AdaptadorCarrito的实例作为参数传递给适配器的构造函数。

示例：

RecyclerItemClickListener

Answer 3

感谢您的回答，我得以解决自己的问题，即更新了活动中的文本视图，但需要另一个班级中的事件的帮助。

首先在适配器的构造函数中添加一个活动

  Activity activity;

public AdaptadorCarrito(ArrayList<CarritoVo> nlistaCarrito, Activity nactivity) {
    nListCarrito = nlistaCarrito;
    this.activity = nactivity;
}

然后以这种方式调用TextView：

 public ViewHolderCarrito onCreateViewHolder(@NonNull final ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_list_carrito,null,false);
    final ViewHolderCarrito myHolder = new ViewHolderCarrito(view);
    final CafeteriaDB cafeteriaDB = new CafeteriaDB(parent.getContext());;
    final CarritoCompras carrito = new CarritoCompras();
   ---->final TextView txtTotalB = (TextView)this.activity.findViewById(R.id.totalB);
    txtTotalB.setText(String.valueOf(cafeteriaDB.getTotal()));

    myHolder.item_list_carrito.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            int newPosition = myHolder.getAdapterPosition();
            cafeteriaDB.eliminarProducto(myHolder.etiNombre.getText().toString(), myHolder.etiInfo.getText().toString());
            eliminarProducto(newPosition);
           Toast.makeText(parent.getContext(),"Producto Eliminado",Toast.LENGTH_SHORT).show();
      ----->  txtTotalB.setText(String.valueOf(cafeteriaDB.getTotal()));
        }

    });
    return myHolder;
}

，最后在活动中创建适配器的实例

   protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_carrito_compras);
    ArrayList<CarritoVo> nLlistaCarrito = null;

    ------>AdaptadorCarrito adapter = new AdaptadorCarrito(nLlistaCarrito,this);

    CafeteriaDB cafeteriaDB = new CafeteriaDB(this);

    TextView txtTotalB = (TextView)findViewById(R.id.totalB);
    txtTotalB.setText(String.valueOf(cafeteriaDB.totalFilas()));

    TextView txtTotalF = (TextView)findViewById(R.id.totalF);
    txtTotalF.setText(String.valueOf(cafeteriaDB.totalFilas()));
}

如何从另一个类刷新TextView？

3 个答案: