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
一、SP存储使用
SP通常用于存储配置信息,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
- 参数1,存储数据的xml文件名称
- 参数2,模式,有3个可选值,默认使用Context.MODE_PRIVATE
使用代码示例
1、登录成功时,存储账户密码
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();
2、打开app时,获取存储的账户密码,显示到页面上
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);
二、SQLite存储使用
- SQLite是一个轻量级数据库,它设计目标是嵌入式的,而且占用资源非常低
- SQLite没有服务器进程,通过文件保存数据,该文件是跨平台的
- 支持null,integer,real,text,blob五种数据类型,实际上SQLite也接受varchar,char,decimal等数据类型,只不过在运算中或保存时会转换成对应的5种数据类型,因此,可以将各种类型数据保存到任何字段中
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;
}
private DBHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
String sql ="create table persons(_id integer primary key autoincrement, name text, sex text, age integer)";
db.execSQL(sql);
}
@Override
public 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);
db.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();
Cursor cursor = db.query("persons", null, null, null, null, null, null);
while (cursor.moveToNext()) {
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();
}
三、Room存储使用
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。
- entities:指定该数据库有哪些表
- version:指定数据库版本号,后续数据库的升级正是依据版本号来判断的
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 {
@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 {
@Insert
void insertPersons(Person... persons);
@Update
void updatePersons(Person... persons);
@Query("delete from Person")
void deleteAllPersons();
@Delete
void deletePersons(Person... persons);
@Query("delete from Person where id in (:ids)")
void deleteByIds(int ...ids);
@Query("select * from Person where id in (:ids)")
List<Person> selectByIds(int ...ids);
@Query("select * from Person order by id desc")
List<Person> 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();
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);
});
}
public void queryRoom(View view) {
AppDatabase db = AppDatabase.getInstance(getApplicationContext());
pool.execute(() -> {
PersonDao dao = db.personDao();
List<Person> list = dao.selectAllPersons();
list.forEach(p-> Log.d("test", p.toString()));
});
}
public void queryRoomById(View view) {
AppDatabase db = AppDatabase.getInstance(getApplicationContext());
pool.execute(() -> {
PersonDao dao = db.personDao();
List<Person> list = dao.selectByIds(3,4);
list.forEach(p-> Log.d("test", p.toString()));
});
}
public void deleteRoom(View view) {
AppDatabase db = AppDatabase.getInstance(getApplicationContext());
pool.execute(() -> {
PersonDao dao = db.personDao();
dao.deleteByIds(1,2);
});
}
Original: https://blog.csdn.net/wlddhj/article/details/127820069
Author: 顽石九变
Title: Android本地数据存储(SP、SQLite、Room)
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