RecyclerView和SQLite：如何从Fragment运行删除数据库记录？

Question

我的RecyclerView的Adapter文件中有一个LongClickListener，用于在RecyclerView列表中侦听CardViews上的LongClicks。监听器链接到RecyclerView活动文件的接口。

在LongClick启动DialogFragment后，步骤1为用户确认删除CardView。该对话框显示“取消”或“确定”选项。 “取消”只是否定了DialogFragment。

步骤2是选择“确定”并且DatabaseHelper文件中的删除代码将从SQLite数据库中删除CardView数据。

步骤3将再次运行RecyclerView Activity，以便RecyclerView列表刷新并显示更新的列表（自数据在数据库中删除后删除了之前的CardView）。

我对第1步很好，因为任何CardView上的LongClick都会按预期启动DialogFragment。我被困在片段行“dbHelper.deletefromDB（UserData userdata）;”中的第2步。 Android Studio警告消息是“无法解析符号'userdata'”。我在这里错过了什么？下面显示了相关的各种文件。

ListActivity file:
...
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);  
    dbList = dbHelper.getAllDataFromDB();
    ...
    ListAdapter mAdapter;        
    mAdapter = new ListAdapter(this, dbList);        
    mRecyclerView.setAdapter(mAdapter);
    mAdapter.setonItemClickListener(new ListAdapter.ClickListener() {
        @Override
        public void onItemLongClick(int position, View view) {
            FragmentManager fm = getSupportFragmentManager();
            DeleteCardViewFragment delCardViewDialog = new DeleteCardViewFragment();
            delCardViewDialog.show(fm, "delcardview dialog");
        }
    });

DatabaseHelper file:
public class DatabaseHelper extends SQLiteOpenHelper {
    ...
    public void deletefromDB(UserData userData) {        
    SQLiteDatabase db = this.getWritableDatabase();
    db.beginTransaction();
    db.delete(DBContract.DBEntry.TABLE_NAME_USERINPUTS, DBContract.DBEntry.COLUMN_NAME_ID + " = ?",
        new String[]{String.valueOf(userData.getId())});
    db.setTransactionSuccessful();
    db.endTransaction();
    if(db.isOpen())
        db.close();
 }    
}

DeleteCardViewFragment file:
public class DeleteCardViewFragment extends DialogFragment {

DatabaseHelper dbHelper;

public DeleteCardViewFragment() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.delcardview_layout, container, false);
    getDialog().setTitle("Delete card");
    dbHelper = new DatabaseHelper(getActivity());

    Button btnCancel = (Button) rootView.findViewById(R.id.btnCancel);
    btnCancel.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            getDialog().cancel();
        }
    });

    Button btnOK = (Button) rootView.findViewById(R.id.btnOK);
    btnOK.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            dbHelper.deletefromDB(UserData userdata);                
            dismiss();

        }
    });    
    ...
 }
}