RecyclerView Null Pointer ERROR

Question

我很困惑，我需要你的帮助开发人员！

MyApp启动ERROR java.lang.NullPointerException：尝试在null对象上调用接口方法'int java.util.List.size（）'引用使用RecyclerView和带有片段的CardView。

 @Override
public int getItemCount()
{
    //ERROR NullPointerException
   return visitaList.size();

}

整个适配器Java代码

公共类VisitaAdapter扩展了RecyclerView.Adapter {

private Context context;
private List<Visita> visitaList;

public VisitaAdapter(Context ctx, List<Visita> visitaList){
    this.context = ctx;
    this.visitaList= visitaList;
}

@Override
public VisitaViewHolder onCreateViewHolder(ViewGroup parent, int viewType){
    //inflating and return our view holder
    LayoutInflater inflater = LayoutInflater.from(context);
    View view = inflater.inflate(R.layout.layout_visita, null);
    return new VisitaViewHolder(view);
}

@Override
public void onBindViewHolder(VisitaViewHolder holder, int position) {
    //getting the product of the specific position
    Visita visita =visitaList.get(position);

    //binding data with the viewholder
    holder.textViewEmpresa.setText(visita.getTitle_empresa());
    holder.textViewMision.setText(visita.getMision());
    holder.textViewFecha.setText(visita.getFecha());

    holder.imageView.setImageDrawable(context.getResources()
            .getDrawable(visita.getImage()));
}

@Override
public int getItemCount()
{
    //ERROR NullPointerException
   return visitaList.size();

}


class VisitaViewHolder extends RecyclerView.ViewHolder {
    TextView textViewEmpresa, textViewMision, textViewFecha;
    ImageView imageView;

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

        textViewEmpresa = itemView.findViewById(R.id.textViewEmpresa);
        textViewMision = itemView.findViewById(R.id.textViewMision);
        textViewFecha = itemView.findViewById(R.id.textViewFecha);
        imageView = itemView.findViewById(R.id.imageView);

    }
}

}

片段启动recyclerview

public class ReplantFrag extends Fragment {

//Adding to the list all items
List<Visita> visitaList;

//The Recycler view
RecyclerView recyclerView;

public ReplantFrag() {
    // Required empty public constructor
}



@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_replanta, container, false);

    //getting the recyclerview from xml
    recyclerView = (RecyclerView) view.findViewById(R.id.reciclerview);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

    VisitaAdapter adapter = new VisitaAdapter(getActivity(), visitaList);

    recyclerView.setAdapter(adapter);

    //agregar items a la maqueta Recycler+CardView


    List<Visita> visitaList = new ArrayList<>();

    //adding items in list
    visitaList.add(new Visita(
            1,
            "ARAUCO S.A.",
            "Revisión Caldera",
            "20-01-2018",
            R.drawable.arauco_logo));

    visitaList.add(new Visita(
            2,
            "ARAUCO S.A.",
            "Inspeccion Nariz Toro",
            "22-01-2018",
            R.drawable.arauco_logo));

    visitaList.add(new Visita(
            3,
            "COLBUN S.A.",
            "Revisión Tuberias",
            "25-01-2018",
            R.drawable.colbun_logo));

    return view;
}

}

谢谢Mate !!

Answer 1

首先创建visitaList对象，然后像这样设置适配器

visitaList = new ArrayList<>();

VisitaAdapter adapter = new VisitaAdapter(getActivity(), visitaList);

recyclerView.setAdapter(adapter);

//adding items in list
visitaList.add(new Visita(
        1,
        "ARAUCO S.A.",
        "Revisión Caldera",
        "20-01-2018",
        R.drawable.arauco_logo));

visitaList.add(new Visita(
        2,
        "ARAUCO S.A.",
        "Inspeccion Nariz Toro",
        "22-01-2018",
        R.drawable.arauco_logo));

visitaList.add(new Visita(
        3,
        "COLBUN S.A.",
        "Revisión Tuberias",
        "25-01-2018",
        R.drawable.colbun_logo));

adapter.notifydatasetchanged();
return view;

Answer 2

您需要在visitaList中添加项目后初始化适配器。这应该做得很好。

List<Visita> visitaList = new ArrayList<>();

//adding items in list
visitaList.add(new Visita(
        1,
        "ARAUCO S.A.",
        "Revisión Caldera",
        "20-01-2018",
        R.drawable.arauco_logo));

visitaList.add(new Visita(
        2,
        "ARAUCO S.A.",
        "Inspeccion Nariz Toro",
        "22-01-2018",
        R.drawable.arauco_logo));

visitaList.add(new Visita(
        3,
        "COLBUN S.A.",
        "Revisión Tuberias",
        "25-01-2018",
        R.drawable.colbun_logo));

//Now that your list is setup you wont have a null list going into your adapter. 
VisitaAdapter adapter = new VisitaAdapter(getActivity(), visitaList);

recyclerView.setAdapter(adapter);

return view;

Answer 3

你的问题是你将Null传递给适配器。

此行List<Visita> visitaList ;被称为声明＆＃34; visitaList为null＆＃34;。

此行visitaList = new ArrayList<>();称为创建。

除非你创建一个对象或为它指定一个引用。它是空的。

所以你有两个选择

1-创建列表并在传递给适配器之前对其进行初始化。

2 - 或者使用new ArrayList<>()创建它并将其传递给适配器，然后在这种情况下你必须告诉适配器列表有一些变化（这是你的初始化）。所以你打电话给adapter.notifydatasetchanged();