RecyclerView 适配器中的空监听器

Question

Android Studio RecyclerView 自定义适配器中的侦听器正在返回 null。

这是界面

  private OnItemClickListener mlistener;

    public interface OnItemClickListener{
        void onItemClick(int position, Boolean paid);
    }
    public void setOnItemClickListener(OnItemClickListener listener){
        mlistener = listener;
    }

这是带有监听器的视图持有者。这旨在将布尔值传递给主要 activity.

 public CartViewHolder(View itemView, ArrayList<Shift> shifts, OnItemClickListener listener) {
            super(itemView);

         
            paid = itemView.findViewById(R.id.due_back_paid);
            containerView = itemView.findViewById(R.id.container);


            paid.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

                    if (listener !=  null){
                        int position = getAdapterPosition();
                        if(position != RecyclerView.NO_POSITION){
                            listener.onItemClick(position, isChecked);
                        }
                    }
                }
            });


            containerView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Shift current = (Shift)containerView.getTag();
                    Intent intent = new Intent(v.getContext(), ViewShiftActivity.class);
                    intent.putExtra("thisShift", current);
                    intent.putExtra("shifts", shifts);
                    v.getContext().startActivity(intent);

                }
            });


        }


    }

    public LoadAdapter(ArrayList<Shift> shifts){
        shiftList = shifts;
    }

    @NonNull
    @Override
    public CartViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.shift_row, parent, false);
        CartViewHolder mvh = new CartViewHolder(view, shiftList, mlistener);
        return mvh;
    }

我在其他项目中使用过此代码，并且有效。我似乎无法弄清楚我错过了什么。

有人要求我加入 activity。以下是这段代码。我还没有在此处的 onItemClick 中添加任何代码。等待监听器工作。

public class EditShiftActivity extends AppCompatActivity implements LoadAdapter.OnItemClickListener{

    private ArrayList<Shift> shifts;
    private RecyclerView lRecyclerView;
    private LoadAdapter lAdapter;
    private RecyclerView.LayoutManager lLayoutManager;
    private View view;
    private FloatingActionButton fab;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_edit_shift);

        Intent intent = getIntent();
        shifts = intent.getParcelableArrayListExtra("shifts");

        fab = findViewById(R.id.add_shift_edit);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent1 = new Intent(EditShiftActivity.this, AddShiftActivity.class);
                intent1.putExtra("shifts", shifts);
                intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                v.getContext().startActivity(intent1);
            }
        });
        
        lRecyclerView = findViewById(R.id.shift_recycler);
        lLayoutManager = new LinearLayoutManager(this);
        lAdapter = new LoadAdapter(shifts);
        lRecyclerView.setLayoutManager(lLayoutManager);
        lRecyclerView.setAdapter(lAdapter);
    }
    
    @Override
    public void onItemClick(int position, Boolean paid) {

    }
}

Answer 1

您正在从 Intent 中检索 ArrayList<Shifts>。在发送到适配器之前检查 shifts arraylist 的大小。如果传递的 arraylist 为空，则有可能适配器将 return null 因此不会显示 lRecyclerView。

在将数据传递给适配器之前添加此条件

//condition to check whether the arraylist is empty or not
if(!shifts.isEmpty()) {

 lAdapter = new LoadAdapter(shifts);
 
 //initialising the adapter
 lRecyclerView.setAdapter(lAdapter);
}

Answer 2

在您的代码中添加以下行 -

lAdapter = new LoadAdapter(shifts);
lAdapter.setOnItemClickListener(this);

RecyclerView 适配器中的空监听器

Null Listener in RecyclerView Adapter

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