Android基础_数据存储

1. Android数据存储的几种形式

   1. 继承SQLiteOpenHelper

      public class NoteSQLiteOpenHelper extends SQLiteOpenHelper {private static final String TAG = "NoteSQLiteOpenHelper";/**     * context 上下文 name 数据库的名称 cursorfactory

   2.  游标工厂 一般设置null 默认游标工厂 version 数据库的版本     * 版本号从1开始的     *      * @param context     */public NoteSQLiteOpenHelper(Context context) {super(context, "note.db", null, 1);}/**     * oncreate 方法 会在数据库第一创建的时候的是被调用 适合做数据库表结构的初始化     */@Overridepublic void onCreate(SQLiteDatabase db) {Log.i(TAG, "oncreate 方法被调用了...");db.execSQL("create table account (id integer primary key autoincrement , name  varchar(20), money varchar(20) )");}@Overridepublic void onUpgrade(SQLiteDatabase db, int arg1, int arg2) {Log.i(TAG,"onupdate 方法被调用了 ,在这个方法里面做更新数据库表结构的操作");db.execSQL("DROP TABLE IF EXISTS " + account);this.onCreate(db);}}

      public class NoteDao {// 因为 任何一个操作都是需要 得到 NoteSQLiteOpenHelper helper// 把他放在构造方法里面初始化private NoteSQLiteOpenHelper helper;public NoteDao(Context context) {helper = new NoteSQLiteOpenHelper(context);}/**     * 添加一条账目信息 到数据库     *      * @param name     *            花销的名称     * @param money     *            金额     */public void add(String name, float money) {SQLiteDatabase db = helper.getWritableDatabase();db.execSQL("insert into account (name,money) values (?,?)",new Object[] { name, money });// 记住 关闭.db.close();}public void delete(int id) {SQLiteDatabase db = helper.getWritableDatabase();db.execSQL("delete from account where id=?", new Object[] { id });db.close();}public void update(int id, float newmoney) {SQLiteDatabase db = helper.getWritableDatabase();db.execSQL("update account set money =? where id=?", new Object[] {newmoney, id });db.close();}/**     * 返回数据库所有的条目     *      * @return     */public List<NoteBean> findAll() {// 得到可读的数据库SQLiteDatabase db = helper.getReadableDatabase();List<NoteBean> noteBeans = new ArrayList<NoteBean>();// 获取到数据库查询的结果游标Cursor cursor = db.rawQuery("select id,money,name from account ", null);while (cursor.moveToNext()) {int id = cursor.getInt(cursor.getColumnIndex("id"));String name = cursor.getString(cursor.getColumnIndex("name"));float money = cursor.getFloat(cursor.getColumnIndex("money"));NoteBean bean = new NoteBean(id, money, name);noteBeans.add(bean);bean = null;}db.close();return noteBeans;}/**     * 模拟一个转账的操作. 使用数据库的事务     *      * @throws Exception     */public void testTransaction() throws Exception {// 得到可写的数据库SQLiteDatabase db = helper.getWritableDatabase();db.beginTransaction(); // 开始事务try {db.execSQL("update account set money = money - 5 where id=? ",new String[] { "2" });db.execSQL("update account set money = money + 5 where id=? ",new String[] { "3" });db.setTransactionSuccessful();} catch (Exception e) {// TODO: handle exception} finally {db.endTransaction();//关闭事务.db.close();}}}

      public class NoteDao2 {private NoteSQLiteOpenHelper helper;public NoteDao2(Context context) {helper = new NoteSQLiteOpenHelper(context);}/**     * 添加一条账目信息 到数据库     *      * @param name     *            花销的名称     * @param money     *            金额     *      * @return true 插入成功 false 失败     */public boolean add(String name, float money) {SQLiteDatabase db = helper.getWritableDatabase();ContentValues values = new ContentValues();values.put("name", name);values.put("money", money);long rawid = db.insert("account", null, values);db.close();if (rawid > 0) {return true;} else {return false;}}public boolean delete(int id) {SQLiteDatabase db = helper.getWritableDatabase();int result = db.delete("account", "id=?", new String[] { id + "" });db.close();if (result > 0) {return true;} else {return false;}}public boolean update(int id, float newmoney) {SQLiteDatabase db = helper.getWritableDatabase();ContentValues values = new ContentValues();values.put("id", id);values.put("money", newmoney);int result = db.update("account", values, "id=?", new String[] { id+ "" });db.close();if (result > 0) {return true;} else {return false;}}/**     * 返回数据库所有的条目     *      * @return     */public List<NoteBean> findAll() {// 得到可读的数据库SQLiteDatabase db = helper.getReadableDatabase();List<NoteBean> noteBeans = new ArrayList<NoteBean>();Cursor cursor = db.query("account", new String[] { "id", "name","money" }, null, null, null, null, null);while (cursor.moveToNext()) {int id = cursor.getInt(cursor.getColumnIndex("id"));String name = cursor.getString(cursor.getColumnIndex("name"));float money = cursor.getFloat(cursor.getColumnIndex("money"));NoteBean bean = new NoteBean(id, money, name);noteBeans.add(bean);bean = null;}db.close();return noteBeans;}}

   3. 获取

      Internal Storage, Store private data on the device memory.(内部存储卡)
      通过

      mContext.getFilesDir()

来得到data/data/包名/File目录

1. External Storage,Store public data on the shared external storage.(外部存储卡)

   1. TextView tv = (TextView) findViewById(R.id.tv_sdsize);
      File path = Environment.getExternalStorageDirectory();
      StatFs stat = new StatFs(path.getPath());
      long blockSize = stat.getBlockSize();
      long availableBlocks = stat.getAvailableBlocks();
      long sizeAvailSize = blockSize * availableBlocks;
      String str = Formatter.formatFileSize(this, sizeAvailSize);
      tv.setText(str);

SharedPreferences

Store private primitive data in key-value pairs.
会在data/data/包名/shared_prefes里面去创建相应的xml文件，根节点是Map，其实内部就是将数据保存到Map集合中，然后将该集合中的数据写到xml文件中进行保存。

1. //获取系统的一个sharedpreference文件

   名字叫 sp

   1. SharedPreferences sp = context.getSharedPreferences("sp", Context.MODE_WORLD_READABLE+Context.MODE_WORLD_WRITEABLE);
      //创建一个编辑器 可以编辑 sp
      Editor editor = sp.edit();
      editor.putString("name", name);
      editor.putString("password", password);
      editor.putBoolean("boolean", false);
      editor.putInt("int", 8888);
      editor.putFloat("float",3.14159f);
      //注意:调用 commit 提交 数据到文件.
      editor.commit();
      //editor.clear();

SQLiteDatabase

Store structured data in a private database. Android平台中嵌入了一个关系型数据库SQLite，和其他数据库不同的是SQLite存储数据时不区分类型，例如一个字段声明为Integer类 型，我们也可以将一个字符串存入，一个字段声明为布尔型，我们也可以存入浮点数。除非是主键被定义为Integer，这时只能存储64位整数创建数据库的 表时可以不指定数据类型，例如：

CREATE TABLE person(id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR(20))
CREATE TABLE person(id INTEGER PRIMARY KEY AUTOINCREMENT, name)

SQLite支持大部分标准SQL语句，增删改查语句都是通用的，分页查询语句和MySQL相同
SELECT * FROM person LIMIT 20 OFFSET 10
SELECT * FROM person LIMIT 10,20
select * from reading_history order by _id desc limit 3, 4;
delete from test where _id in (select _id from test ORDER BY _id DESC limit 3, 20)

Network
Store data on the web with your own network server.

清除缓存&清除数据
清除数据会清除/data/data/包名中的所有文件

getCacheDir()  /data/data/<当前应用程序包名>/cache/，清除缓存的时候会清除该目录中的内容