Android 如何使用SQLite保存数据

public final class feedreadercontract {
    // to prevent someone from accidentally instantiating the contract class,
    // make the constructor private.
    private feedreadercontract() {}
    /* inner class that defines the table contents */
    public static class feedentry implements basecolumns {
    	// 表名
        public static final string table_name = "entry";
        // 列名
        public static final string column_name_title = "title";
        // 列名
        public static final string column_name_subtitle = "subtitle";
    }
}

// 创建数据库表
private static final string sql_create_entries =
    "create table " + feedentry.table_name + " (" +
    feedentry._id + " integer primary key," +
    feedentry.column_name_title + " text," +
    feedentry.column_name_subtitle + " text)";
// 删除数据库表
private static final string sql_delete_entries =
    "drop table if exists " + feedentry.table_name;

public class feedreaderdbhelper extends sqliteopenhelper {
    // if you change the database schema, you must increment the database version.
    public static final int database_version = 1;
    public static final string database_name = "feedreader.db";
	private static final string sql_create_entries =
    	"create table " + feedentry.table_name + " (" +
    	feedentry._id + " integer primary key," +
    	feedentry.column_name_title + " text," +
    	feedentry.column_name_subtitle + " text)";
	private static final string sql_delete_entries =
		"drop table if exists " + feedentry.table_name;
    public feedreaderdbhelper(context context) {
        super(context, database_name, null, database_version);
    }
    public void oncreate(sqlitedatabase db) {
    	// 创建数据库表
        db.execsql(sql_create_entries);
    }
    public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {
        // this database is only a cache for online data, so its upgrade policy is
        // to simply to discard the data and start over
        db.execsql(sql_delete_entries);
        oncreate(db);
    }
    public void ondowngrade(sqlitedatabase db, int oldversion, int newversion) {
        onupgrade(db, oldversion, newversion);
    }
}

feedreaderdbhelper dbhelper = new feedreaderdbhelper(getcontext());

// gets the data repository in write mode
sqlitedatabase db = dbhelper.getwritabledatabase();
// create a new map of values, where column names are the keys
contentvalues values = new contentvalues();
values.put(feedentry.column_name_title, title);
values.put(feedentry.column_name_subtitle, subtitle);
// insert the new row, returning the primary key value of the new row
long newrowid = db.insert(feedentry.table_name, null, values);

public long insert (string table, 
                string nullcolumnhack, 
                contentvalues values)

sqlitedatabase db = dbhelper.getreadabledatabase();
// define a projection that specifies which columns from the database
// you will actually use after this query.
string[] projection = {
    basecolumns._id,
    feedentry.column_name_title,
    feedentry.column_name_subtitle
    };
// filter results where "title" = 'my title'
string selection = feedentry.column_name_title + " = ?";
string[] selectionargs = { "my title" };
// how you want the results sorted in the resulting cursor
string sortorder =
    feedentry.column_name_subtitle + " desc";
cursor cursor = db.query(
    feedentry.table_name,   // the table to query
    projection,             // the array of columns to return (pass null to get all)
    selection,              // the columns for the where clause
    selectionargs,          // the values for the where clause
    null,                   // don't group the rows
    null,                   // don't filter by row groups
    sortorder               // the sort order
    );

public cursor query (string table, 	// 要查询的表名，不能为空
                string[] columns, 	// 要返回的列的列表。传递 null 将返回所有列
                string selection, 	// 声明要返回哪些行的过滤器，传递 null 将返回给定表的所有行
                string[] selectionargs,  // 可以在选择中包含 ?，它将被选择参数中的值替换，按照它们在选择中出现的顺序
                string groupby, 	// 分组过滤器，传递 null 将导致行不被分组
                string having, 		// 如果使用行分组，则过滤器声明游标中包含哪些行组，传递 null 将导致包含所有行组
                string orderby)		// 对行进行排序，传递 null 将使用默认排序顺序，该顺序可能是无序的

list itemids = new arraylist<>();
while(cursor.movetonext()) {
  long itemid = cursor.getlong(
      cursor.getcolumnindexorthrow(feedentry._id));
  itemids.add(itemid);
}
cursor.close();

// define 'where' part of query.
string selection = feedentry.column_name_title + " like ?";
// specify arguments in placeholder order.
string[] selectionargs = { "mytitle" };
// issue sql statement.
int deletedrows = db.delete(feedentry.table_name, selection, selectionargs);

// return: 如果传入 whereclause，则影响的行数，否则为 0。要删除所有行并获取计数，请传递“1”作为 whereclause。
public int delete (string table, 		// 要操作的表名，不能为空
                string whereclause, 	// 删除时应用的可选 where 子句。传递 null 将删除所有行。
                string[] whereargs)		// 可以在 where 子句中包含 ?s，它将被 whereargs 中的值替换。这些值将绑定为字符串。如果 whereclause 为 null 或不包含 ?s，则 whereargs 可能为 null。

sqlitedatabase db = dbhelper.getwritabledatabase();
// new value for one column
string title = "mynewtitle";
contentvalues values = new contentvalues();
values.put(feedentry.column_name_title, title);
// which row to update, based on the title
string selection = feedentry.column_name_title + " like ?";
string[] selectionargs = { "myoldtitle" };
int count = db.update(
    feedreaderdbhelper.feedentry.table_name,
    values,
    selection,
    selectionargs);

public int update (string table, 			// 要更新的表名，不能为null
                contentvalues values, 		// 从列名到新列值的映射。 null 是一个有效值，将被转换为 null。
                string whereclause, 		// 更新时应用的可选 where 子句。传递 null 将更新所有行。
                string[] whereargs)			// 可以在 where 子句中包含 ?s，它将被 whereargs 中的值替换。这些值将绑定为字符串。如果 whereclause 为 null 或不包含 ?s，则 whereargs 可能为 null。

@override
protected void ondestroy() {
    dbhelper.close();
    super.ondestroy();
}

$ adb -s emulator-5554 shell
$ sqlite3 /data/data/com.example.app/databases/rssitems.db
sqlite version 3.3.12
enter ".help" for instructions