java - 获取同一个对象到Android ListView

Question

我尝试在 Android 中开发我的第一个应用程序，但遇到了一个错误。我需要从 SQLite 数据库获取对象并在 ListView 中显示它们。这是我的适配器的代码:

public class ReminderListAdapter extends ArrayAdapter<Reminder> {
private Context mContext;
private int mResource;

public ReminderListAdapter(@NonNull Context context, int resource, @NonNull ArrayList<Reminder> objects) {
    super(context, resource, objects);
    mContext = context;
    mResource = resource;

}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    int id = getItem(position).getId();
    String name = getItem(position).getName();
    String hour = getItem(position).getHour();
    String date = getItem(position).getDate();

    LayoutInflater inflater = LayoutInflater.from(mContext);
    convertView = inflater.inflate(mResource, parent, false);

    TextView resId = convertView.findViewById(R.id.textId);
    TextView resName = convertView.findViewById(R.id.textName);
    TextView resHour = convertView.findViewById(R.id.textHour);
    TextView resDate = convertView.findViewById(R.id.textDate);

    resId.setText(String.valueOf(id));
    resName.setText(name);
    resHour.setText(hour);
    resDate.setText(date);

    return convertView;
}

这是我需要从数据库发布对象的 Activity 代码:

public class EditActivity extends AppCompatActivity {

DBHelper dbHelper;
SQLiteDatabase database;
private ListView listView;
private TextView countRem;
private String count;
ArrayList<Reminder> ReminderList = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_edit);
    dbHelper = new DBHelper(this);
    database = dbHelper.getWritableDatabase();
    listView =(ListView) findViewById(R.id.ListOfReminders);
    countRem =(TextView) findViewById(R.id.textView);



    Cursor cursor = database.query(TABLE_REMINDERS, null, null,null,null,null,null);
    getRemindersCount();
    count = Integer.toString(getRemindersCount());
    countRem.setText(count);
    if(cursor.moveToFirst())
    {
        int idIndex = cursor.getColumnIndex(DBHelper.KEY_ID);
        int nameIndex = cursor.getColumnIndex(DBHelper.KEY_NAME);
        int hourIndex = cursor.getColumnIndex(DBHelper.KEY_HOUR);
        int dateIndex = cursor.getColumnIndex(DBHelper.KEY_DATE);
        String name = Integer.toString(nameIndex);
        String hour = Integer.toString(hourIndex);
        String date = Integer.toString(dateIndex);
        do{
            ReminderList.add(new Reminder(idIndex, name, hour, date));
            ReminderListAdapter adapter = new ReminderListAdapter(this, R.layout.reminder_view, ReminderList);
            listView.setAdapter(adapter);

        } while(cursor.moveToNext());
    } else
        Log.d("mLog", "0 rows in db");

}

public int getRemindersCount(){
    long NrOfReminders = DatabaseUtils.queryNumEntries(database, TABLE_REMINDERS);
    int count = (int)NrOfReminders;
    return count;
}

结果，我在 ListView 中得到相同的输出。对象1:ID:0，名称:1，小时:2，日期:3。该数据与数据库中的数据不匹配。而且，这个输出适用于每个对象。有什么错误吗？如果这是一个愚蠢的错误，我很抱歉，这是第一个应用程序。

Answer 1

cursor.getColumnIndex(...) 仅返回行的列索引。要获取该列中的值，您有几个选项:

• 如果事先知道数据类型，则可以直接调用光标上相应的方法。例如，如果DBHelper.KEY_NAME列包含一个String，我们可以直接使用cursor.getString(cursor.getColumnIndex(DBHelper. KEY_NAME))

• 如果没有，您可以尝试调用 cursor.getType(int columnIndex)获取基础类型，然后根据返回值调用游标上相应的方法。

简而言之，代码的问题在于您获取的是列索引 (getColumnIndex)，而不是列值 (getFloat、getInt、getString等):

    ...
    int idIndex = cursor.getColumnIndex(DBHelper.KEY_ID);
    int nameIndex = cursor.getColumnIndex(DBHelper.KEY_NAME);
    int hourIndex = cursor.getColumnIndex(DBHelper.KEY_HOUR);
    int dateIndex = cursor.getColumnIndex(DBHelper.KEY_DATE);
    String name = cursor.getString(nameIndex);
    String hour = cursor.getString(hourIndex);
    String date = cursor.getString(dateIndex);
  ...