我在安卓学习sqlite。对于sqlite,我正在引用developer.android.com。但我在读代码时有些困惑。他们写了构造函数来防止
实例化FeedReaderContract
类,但它们没有在任何地方定义FeedReaderContract
类以及FeedReaderContract
和FeedReaderContract
之间的关系。
我指的是。我提供代码。如何在OpenHelper类中定义内部类。有人能给我提个好办法吗?.
例如,此代码段定义单个表的表名和列名:
public static abstract class FeedEntry implements BaseColumns
{
public static final String TABLE_NAME = "entry";
public static final String COLUMN_NAME_ENTRY_ID = "entryid";
public static final String COLUMN_NAME_TITLE = "title";
public static final String COLUMN_NAME_SUBTITLE = "subtitle";
...
}
为了防止有人意外地实例化契约类,请给它一个空的构造函数。
//Prevents the FeedReaderContract class from being instantiated.
private FeedReaderContract() {}
最佳答案
我理解为:
public static class FeedReaderContract{
// Prevents the FeedReaderContract class from being instantiated.
private FeedReaderContract() {}
//The FeedEntry table definition
public static abstract class FeedEntry implements BaseColumns {
public static final String TABLE_NAME = "entry";
public static final String COLUMN_NAME_ENTRY_ID = "entryid";
public static final String COLUMN_NAME_TITLE = "title";
public static final String COLUMN_NAME_SUBTITLE = "subtitle";
...
}
//more tables definition
}
因此,您不能实例化契约,但可以访问所有内部类常量。如示例行:
private static final String SQL_CREATE_ENTRIES =
"CREATE TABLE " + FeedReaderContract.FeedEntry.TABLE_NAME + " (" +
FeedReaderContract.FeedEntry._ID + " INTEGER PRIMARY KEY," //continues
访问
FeedEntry
类中内部类的TABLE_NAME
常量(_ID
和FeedReaderContract
)。希望有帮助。