项目无法在回收站视图中设置

Question

适配器代码

 public class ButtonGroupAdp extends RecyclerView.Adapter<ButtonGroupAdp.MyViewHolder> {


    List<ButtonGroup> mList;

    private ItemClickListener mClickListener;
    Context context;
    private int screenWidth;

    public ButtonGroupAdp(List<ButtonGroup> mList, Context context) {
        this.mList = mList;
        this.context = context;
        WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        Display display = wm.getDefaultDisplay();
        Point size = new Point();
        display.getSize(size);
        screenWidth = size.x;
    }


    public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        TextView txtTitle;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            txtTitle = itemView.findViewById(R.id.tv_name);
        }

        @Override
        public void onClick(View view) {
            if (mClickListener != null) mClickListener.onItemClick(view, getAdapterPosition());
        }
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(context);
        View view = layoutInflater.inflate(R.layout.list_groupname, parent, false);

        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {

        ButtonGroup datum = mList.get(position);
        holder.txtTitle.setText("" + datum.getGroupName());
        datum.notifyAll();


    }

    public interface ItemClickListener {
        void onItemClick(View view, int position);
    }


    @Override
    public int getItemCount() {
        return mList.size();
    }
}

这是我的主要活动代码

badp = new ButtonGroupAdp(mlist, this);

    mlist = new ArrayList<>();
    mlist =  mobexInAppDb.getAllProductList(site);
   myRecyclerView.setAdapter(badp);

这是 m 从 sqlite 获取值的地方

 public List<ButtonGroup> getAllProductList(String siteCode) {
    List<ButtonGroup> buttonGroups = new ArrayList<>();
    Cursor cursor = null;
    SQLiteDatabase db = this.getWritableDatabase();
    cursor = db.rawQuery("SELECT DISTINCT groupName,groupId FROM ButtonGroups where parentGroupId='"+null+"' and siteCode='"+siteCode+"'", null);
    if (cursor.getCount() != 0) {
        while (cursor.moveToNext()) {
            ButtonGroup buttonGroup = new ButtonGroup(cursor.getString(0),cursor.getString(1));
            buttonGroups.add(buttonGroup);
        }
    }
    cursor.close();
    return buttonGroups;
}

基本上我想把这些数据放在我的水平回收器视图中，触摸每个项目我应该知道哪个是点击但不知道为什么我会遇到这个错误请帮助我 这是我得到的错误

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mobex.inapp, PID: 17931
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
    at com.mobex.inapp.Adapter.ButtonGroupAdp.getItemCount(ButtonGroupAdp.java:81)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4044)
    at androidx.recyclerview.widget.RecyclerView.onMeasure(RecyclerView.java:3534)

Answer 1

您的mlist 是null

您首先需要初始化您的mlist，然后将其传递给您的ButtonGroupAdp 适配器，如下代码所示

示例代码

mlist = new ArrayList<>();
badp = new ButtonGroupAdp(mlist, this);
mlist =  mobexInAppDb.getAllProductList(site);
myRecyclerView.setAdapter(badp);

更新

在 ArrayList 中添加数据后，您需要 notify 适配器

mlist = new ArrayList<>();
adp = new ButtonGroupAdp(mlist, this);
myRecyclerView.setAdapter(badp);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mlist =  mobexInAppDb.getAllProductList(site);
adp.notifyDataSetChanged();

Answer 2

您必须在将您的 mList 传递给 ButtonGroupAdp 之前对其进行初始化

这应该可以解决。

只需替换

List<ButtonGroup> mList;

有

List<ButtonGroup> mList = new ArrayList<>();

更新

改变这个

badp = new ButtonGroupAdp(mlist, this);
    mlist = new ArrayList<>();
    mlist =  mobexInAppDb.getAllProductList(site);
   myRecyclerView.setAdapter(badp);

到

mlist = new ArrayList<>();
badp = new ButtonGroupAdp(mlist, this);
myRecyclerView.setAdapter(badp);
myRecyclerView.setLayoutManager(new LinearLayoutManager(this, 
LinearLayoutManager.HORIZONTAL, true));
mlist =  mobexInAppDb.getAllProductList(site);
badp.notifyDataSetChanged();