Android-使用游标从数据库表中获取单个值

I'm using cursors to retrieve data from a database. I know how to retrieve entire columns to use on listviews and such, but I'm struggling to find a way to retrieve a single value.

我正在使用游标从数据库中检索数据。我知道如何检索整个列以用于listviews等，但我很难找到一种方法来检索单个值。

Let's say I have a table with two columns ("_id" and "Name") and I have ten records (rows) in that table. How would I get, for example, the Name in the third row? Considering I defined a cursor that reads that table:

假设我有一个包含两列（“_id”和“Name”）的表，我在该表中有十个记录（行）。例如，我如何得到第三行中的名字？考虑到我定义了一个读取该表的游标：

public Cursor getMyNameInfo() {

    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();


    String sqlTables = "MyNames";
    qb.setTables(sqlTables);
    Cursor c = qb.query(db, null, null, null,
            null, null, null);  

    c.moveToFirst();
    return c;
    }

4 个解决方案

#1

Instead of c.moveToFirst() use c.moveToPosition(2) (Cursor indexes are zero-based hence '2' is the third record).

而不是c.moveToFirst（）使用c.moveToPosition（2）（游标索引是从零开始的，因此'2'是第三个记录）。

Remember to check that the Cursor has valid data first though.

请记住先检查Cursor是否有有效数据。

EDIT:

编辑：

Once you've moved the cursor to the 3rd record as I explain above, use the following to just get the value of the "Name" column.

按照上面的说明将光标移动到第3条记录后，使用以下命令获取“Name”列的值。

String theName = c.getString(getColumnIndex("Name"));

#2

Cursor cursor = dbHelper.getdata();

        System.out.println("colo" + cursor.getColumnCount() + ""
                + cursor.getCount());

        cursor.moveToFirst();

        if (cursor != null) {

            while (cursor.isAfterLast() == false) {

                String chktitle = title.trim().toString();
                String str = cursor.getString(cursor.getColumnIndex("title"));

                System.out.println("title :: "
                        + cursor.getString(cursor.getColumnIndex("title")));
                System.out.println("date :: "
                        + cursor.getString(cursor.getColumnIndex("date")));
                System.out.println("desc :: "
                        + cursor.getString(cursor.getColumnIndex("desc")));

                if (chktitle.equals(str) == true) {
                    tvAddfavorite.setText("Remove Favorite");
                    break;
                }
                cursor.moveToNext();
            }
        }
        cursor.close();

#3

Add a WHERE clause:

添加WHERE子句：

qb.appendWhere("_id = 2");

#4

Thanks to the answers above I created the following method to give the value of an item from another column but in the same row.

感谢上面的答案，我创建了以下方法，以便从另一列但同一行中提供项目的值。

public String getValueFromColumn(int position, String tableName, String columnToGetValueFrom) {

    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();

    qb.setTables(tableName);
    Cursor c = qb.query(db, null, null, null,
            null, null, null);

    c.moveToPosition(position);
    String neededValue = c.getString(c.getColumnIndex(columnToGetValueFrom));
    return neededValue;
}

Hope it helps anyone.

希望它能帮助任何人。

#1