android - 从数据库中的列获取值

Question

我从数据库中的“threadid”列获取值。问题是它从上一条记录/行获取值。当我尝试获取第一条记录时，我的应用程序崩溃了，如何解决这个问题，问题是什么？

long id;
long threadid = datasource.getthreadid(id);
Toast.makeText(getActivity(), String.valueOf(threadid), Toast.LENGTH_SHORT).show();

public long getthreadid(long id)
  {

      String ide=String.valueOf(id);
      String queryz = "SELECT " + MySQLiteHelper.COLUMN_THREADID 
                + " FROM " + MySQLiteHelper.TABLE_NAME 
                + " WHERE " + MySQLiteHelper.COLUMN_ID + "=" + ide;
      Cursor cursor = database.rawQuery(queryz, null);
      cursor.moveToFirst();
     // cursor.moveToPosition(Integer.parseInt(String.valueOf(id)));
     long threadid= cursor.getLong(cursor.getColumnIndex("threadid"));

      cursor.close();
    return threadid;

  }

Answer 1

如果您只期望一行。那么做这样的事情可能会有用。

long threadid;

if (cursor.moveToFirst())
{
    threadid = cursor.getLong(cursor.getColumnIndex("threadid"));
}
else
{
    // ah oh, we do not have this id!
    // do something here if you need to
}

此外，如果您要使用字符串，我建议您绑定(bind)参数。我知道你已经提前很久了，但是对于字符串你可以这样做。

  String queryz = "SELECT " + MySQLiteHelper.COLUMN_THREADID 
            + " FROM " + MySQLiteHelper.TABLE_NAME 
            + " WHERE " + MySQLiteHelper.COLUMN_ID + " = ?";
  Cursor cursor = database.rawQuery(queryz, new String[]{ide});