android - _COUNT 列的用途是什么？

Question

Android 在 BaseColumns 接口(interface)中指定了 super 方便的 _id 列，其用法在 this question 中有很好的解释。 ，但是 _count 的用途是什么？目录中的行数，什么目录？

public interface BaseColumns
{
    /**
     * The unique ID for a row.
     * <P>Type: INTEGER (long)</P>
     */
    public static final String _ID = "_id";

    /**
     * The count of rows in a directory.
     * <P>Type: INTEGER</P>
     */
    public static final String _COUNT = "_count";
}

Answer 1

如 this tutorial 中所述:

Every provider can also report the number of records returned as the _COUNT column; its value is the same for all rows.

Here is an example result set for the query in the previous section:

_ID  _COUNT   NAME           NUMBER
44   3        Alan Vain      212 555 1234
13   3        Bully Pulpit   425 555 6677
53   3        Rex Cars       201 555 4433