Android 数据存储

本章节将介绍Android中的各种数据存储方式，包括SharedPreferences、SQLite、Room、文件存储等。

SharedPreferences

核心特性

轻量级键值对存储
适用于小规模数据
支持多种数据类型

最佳实践

// 使用委托属性
class PreferenceManager(context: Context) {
    private val prefs = context.getSharedPreferences("app_settings", Context.MODE_PRIVATE)
    
    var username: String by Delegates.observable(prefs.getString("username", "")!!) { _, _, new ->
        prefs.edit().putString("username", new).apply()
    }
    
    var isFirstLaunch: Boolean
        get() = prefs.getBoolean("is_first_launch", true)
        set(value) = prefs.edit().putBoolean("is_first_launch", value).apply()
}

Room数据库

核心组件

Entity：数据表实体
DAO：数据访问对象
Database：数据库类

实现示例

// Entity定义
@Entity(tableName = "users")
data class User(
    @PrimaryKey val id: Long,
    @ColumnInfo(name = "name") val name: String,
    @ColumnInfo(name = "email") val email: String
)
 
// DAO接口
@Dao
interface UserDao {
    @Query("SELECT * FROM users")
    suspend fun getAllUsers(): List<User>
    
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertUser(user: User)
    
    @Delete
    suspend fun deleteUser(user: User)
}
 
// Database类
@Database(entities = [User::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao
    
    companion object {
        @Volatile
        private var INSTANCE: AppDatabase? = null
        
        fun getInstance(context: Context): AppDatabase {
            return INSTANCE ?: synchronized(this) {
                Room.databaseBuilder(
                    context.applicationContext,
                    AppDatabase::class.java,
                    "app_database"
                ).build().also { INSTANCE = it }
            }
        }
    }
}

文件存储

存储类型

内部存储
外部存储
缓存目录

使用示例

// 文件操作工具类
class FileManager(private val context: Context) {
    // 写入内部存储
    fun writeToInternal(fileName: String, content: String) {
        context.openFileOutput(fileName, Context.MODE_PRIVATE).use {
            it.write(content.toByteArray())
        }
    }
    
    // 读取内部存储
    fun readFromInternal(fileName: String): String {
        return context.openFileInput(fileName).bufferedReader().useLines { lines ->
            lines.joinToString("\n")
        }
    }
    
    // 写入外部存储
    fun writeToExternal(fileName: String, content: String) {
        if (isExternalStorageWritable()) {
            val file = File(context.getExternalFilesDir(null), fileName)
            file.writeText(content)
        }
    }
}

ContentProvider

使用场景

跨应用数据共享
统一数据访问接口
数据访问权限控制

实现示例

class UserProvider : ContentProvider() {
    private lateinit var dbHelper: DatabaseHelper
    
    override fun onCreate(): Boolean {
        dbHelper = DatabaseHelper(context!!)
        return true
    }
    
    override fun query(
        uri: Uri,
        projection: Array<String>?,
        selection: String?,
        selectionArgs: Array<String>?,
        sortOrder: String?
    ): Cursor? {
        val db = dbHelper.readableDatabase
        return db.query(
            "users",
            projection,
            selection,
            selectionArgs,
            null,
            null,
            sortOrder
        )
    }
    
    // 其他CRUD操作实现...
}

数据加密

加密方式

SharedPreferences加密
数据库加密
文件加密

安全最佳实践

// 使用EncryptedSharedPreferences
val masterKey = MasterKey.Builder(context)
    .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
    .build()
 
val encryptedPrefs = EncryptedSharedPreferences.create(
    context,
    "secret_prefs",
    masterKey,
    EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
    EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
)
 
// 使用加密数据库
Room.databaseBuilder(context, AppDatabase::class.java, "encrypted_db")
    .openHelperFactory(SupportFactory(SQLiteDatabase.getBytes("password".toCharArray())))
    .build()

Security Database