Android本地数据存储常用的有三种方式
1、SP存储,key-value的方式存储在本地的xml文件中,/data/data/xxx.xx/shared_prefs/xxx.xml
2、sqlite存储
3、room存储
SP通用用于存储配置信息,如果app风格主题、登录用户名、密码等少量数据,不适于存储大量数据。
在Activity中通过调用基类方法getSharedPreferences()获取操作实例对象
该方法需要传入两个参数
使用代码示例
1、登录成功时,存储账户密码
// 登录成功记录本次登录信息
SharedPreferences sp = getSharedPreferences("login_sp_info", Context.MODE_PRIVATE);
SharedPreferences.Editor edit = sp.edit();
edit.putString("username",usernameEditText.getText().toString());
edit.putString("password",passwordEditText.getText().toString());
edit.apply();//提交数据保存
2、打开app时,获取存储的账户密码,显示到页面上
//设置上次记录的用户信息
SharedPreferences sp = getSharedPreferences("login_sp_info", Context.MODE_PRIVATE);
String username = sp.getString("username","");
String password = sp.getString("password","");
companycodeEditText.setText(companycode);
usernameEditText.setText(username);
passwordEditText.setText(password);
Android系统推荐使用SQLiteOpenHelper的子类创建数据库,因此需要创建一个类继承自SQLiteOpenHelper,并重写该类的onCreate和onUpgrade方法即可。
这里使用单例模式创建,在首次调用DBHelper时就会自动执行创建数据库操作
public class DBHelper extends SQLiteOpenHelper {private volatile static DBHelper instance;public static DBHelper getInstance(Context context) {if (instance == null) {synchronized (DBHelper.class) {if (instance == null) {instance = new DBHelper(context, "mytest.db", null, 1);}}}return instance;}/*** 作为SQLiteOpenHelper子类必须有的构造方法* @param context 上下文参数* @param name 数据库名字* @param factory 游标工厂 ,通常是null* @param version 数据库的版本*/private DBHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {super(context, name, factory, version);}/*** 数据库第一次被创建时调用该方法* @param db*/@Overridepublic void onCreate(SQLiteDatabase db) {// 初始化数据库的表结构,执行一条建表的SQL语句String sql ="create table persons(_id integer primary key autoincrement, name text, sex text, age integer)";db.execSQL(sql);}/*** 当数据库的版本号增加调用* @param db* @param oldVersion* @param newVersion*/@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
}
SQLiteOpenHelper提供了直接执行sql语句的方法execSQL()
,同时也提供了对应的增删改查四个方法insert、delete、update、query
方法一,执行sql
public void insert(View view) {DBHelper instance = DBHelper.getInstance(this);SQLiteDatabase db = instance.getWritableDatabase();if (!db.isOpen()) {return;}String sql = "insert into persons(name,sex,age) values('张三','男',20)";db.execSQL(sql);db.close();
}
方法二,执行insert方法
public void insert2(View view) {DBHelper instance = DBHelper.getInstance(this);SQLiteDatabase db = instance.getWritableDatabase();if (!db.isOpen()) {return;}ContentValues values = new ContentValues();values.put("name", "王五");values.put("sex", "女");values.put("age", 30);// 插入数据// insert方法参数1:要插入的表名// insert方法参数2:如果发现将要插入的行为空时,会将这个列名的值设为null// insert方法参数3:contentValuedb.insert("persons", null, values);db.close();
}
public void deleteData(View view) {DBHelper instance = DBHelper.getInstance(this);SQLiteDatabase db = instance.getWritableDatabase();if (!db.isOpen()) {return;}String sql = "delete from persons where _id=?";db.execSQL(sql, new Object[]{3});db.close();
}
public void updateData(View view) {DBHelper instance = DBHelper.getInstance(this);SQLiteDatabase db = instance.getWritableDatabase();if (!db.isOpen()) {return;}String sql = "update persons set name =? where _id=?";db.execSQL(sql, new Object[]{"李四", 2});db.close();
}
方法一,执行sql
public void query(View view) {DBHelper instance = DBHelper.getInstance(this);SQLiteDatabase db = instance.getReadableDatabase();if (!db.isOpen()) {return;}Cursor cursor = db.rawQuery("select * from persons", null);while (cursor.moveToNext()) {int _id = cursor.getInt(cursor.getColumnIndex("_id"));String name = cursor.getString(cursor.getColumnIndex("name"));String sex = cursor.getString(cursor.getColumnIndex("sex"));int age = cursor.getInt(cursor.getColumnIndex("age"));Log.d("test", "query: _id: " + _id + ", name: " + name + ",sex: " + sex + ",age: " + age);}cursor.close();db.close();
}
方法二,执行query方法
public void query2(View view) {DBHelper instance = DBHelper.getInstance(this);SQLiteDatabase db = instance.getReadableDatabase();// 参数1:table_name// 参数2:columns 要查询出来的列名。相当于 select *** from table语句中的 ***部分// 参数3:selection 查询条件字句,在条件子句允许使用占位符“?”表示条件值// 参数4:selectionArgs :对应于 selection参数 占位符的值// 参数5:groupby 相当于 select *** from table where && group by ... 语句中 ... 的部分// 参数6:having 相当于 select *** from table where && group by ...having %%% 语句中 %%% 的部分// 参数7:orderBy :相当于 select ***from ?? where&& group by ...having %%% order by@@语句中的@@ 部分,如: personid desc(按person 降序)Cursor cursor = db.query("persons", null, null, null, null, null, null);while (cursor.moveToNext()) { // 游标只要不是在最后一行之后,就一直循环int _id = cursor.getInt(0);String name = cursor.getString(1);String sex = cursor.getString(2);int age = cursor.getInt(3);Log.d("test", "query: _id: " + _id + ", name: " + name + ",sex: " + sex + ",age: " + age);}cursor.close();db.close();
}
Room在SQLite基础上做了ORM封装,使用起来类似JPA,不需要写太多的sql。
//room
def room_version="2.4.2"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
//implementation "androidx.room:room-rxjava2:$room_version"
//implementation "androidx.room:room-rxjava3:$room_version"
//implementation "androidx.room:room-guava:$room_version"
//testImplementation "androidx.room:room-testing:$room_version"
//implementation "androidx.room:room-paging:2.5.0-alpha01"
1、@Database:Room数据库对象。该类需要继承自RoomDatabase,通过Room.databaseBuilder()结合单例设计模式,完成数据库的创建工作。我们创建的Dao对象,在这里以抽象方法的形式返回,只需一行代码即可。
2、@Entity:该类与Room中表关联起来。tableName属性可以为该表设置名字,如果不设置,则表名与类名相同。
3、@PrimaryKey:用于指定该字段作为表的主键。
4、@ColumnInfo:设置该字段存储在数据库表中的名字并指定字段的类型;默认字段名和属性名一样
5、@Ignore:忽略该字段
1、创建实体类,对应数据库中一张表,使用注解@Entity
@Entity
public class Person {// 主键,自增长@PrimaryKey(autoGenerate = true)private int id;private String name;private String sex;private int age;
}
2、创建Dao类,用于操作数据,使用注解@Dao
@Dao
public interface PersonDao {// 插入@Insertvoid insertPersons(Person... persons);// 修改@Updatevoid updatePersons(Person... persons);// 删除所有@Query("delete from Person")void deleteAllPersons();// 删除指定实体@Deletevoid deletePersons(Person... persons);// 根据id删除@Query("delete from Person where id in (:ids)")void deleteByIds(int ...ids);// 根据id查询@Query("select * from Person where id in (:ids)")List selectByIds(int ...ids);// 查询所有@Query("select * from Person order by id desc")List selectAllPersons();
}
3、创建数据库对象Database,继承RoomDatabase,使用单例模式返回实例
@Database(entities = {Person.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {public abstract PersonDao personDao();private volatile static AppDatabase instance;public static AppDatabase getInstance(Context context){if (instance == null) {synchronized (DBHelper.class) {if (instance == null) {instance = Room.databaseBuilder(context, AppDatabase.class, "person.db").build();}}}return instance;}
}
4、在Activity中使用
Room数据操作必须在异步线程中执行,所以在Activity中使用线程池执行
ExecutorService pool = Executors.newCachedThreadPool();// 插入数据
public void insertRoom(View view) {AppDatabase db = AppDatabase.getInstance(getApplicationContext());pool.execute(() -> {PersonDao dao = db.personDao();Person p1 = new Person("用户1", "男", 18);Person p2 = new Person("用户2", "男", 28);Person p3 = new Person("用户3", "男", 38);dao.insertPersons(p1, p2, p3);});}// 查询数据
public void queryRoom(View view) {AppDatabase db = AppDatabase.getInstance(getApplicationContext());pool.execute(() -> {PersonDao dao = db.personDao();List list = dao.selectAllPersons();list.forEach(p-> Log.d("test", p.toString()));});
}// 根据id查询
public void queryRoomById(View view) {AppDatabase db = AppDatabase.getInstance(getApplicationContext());pool.execute(() -> {PersonDao dao = db.personDao();List list = dao.selectByIds(3,4);list.forEach(p-> Log.d("test", p.toString()));});
}// 删除
public void deleteRoom(View view) {AppDatabase db = AppDatabase.getInstance(getApplicationContext());pool.execute(() -> {PersonDao dao = db.personDao();dao.deleteByIds(1,2);});
}