Android Jetpack 之DataStore 学习笔记

DataStore definition

One of the primary benefits of DataStore is the asynchronous API.aimed at replacing SharedPreferences.Data is stored asynchronously, consistently, and transactionally, overcoming most of the drawbacks of SharedPreferences.

另外，DataStore能存储基本的键值对，也能存储数据对象类型。

0.Setup

//添加依赖

implementation("androidx.datastore:datastore:1.0.0")
implementation("androidx.datastore:datastore-preferences:1.0.0")

1.Preferences DataStore（SharedPreferences）

• Create a Preferences DataStore

// At the top level of your kotlin file:
val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "settings")

• Read from a Preferences DataStore

val EXAMPLE_COUNTER = intPreferencesKey("example_counter")
val exampleCounterFlow: Flow<Int> = context.dataStore.data
  .map { preferences ->
    // No type safety.
    preferences[EXAMPLE_COUNTER] ?: 0
}

• Write to a Preferences DataStore

suspend fun incrementCounter() {
  context.dataStore.edit { settings ->
    val currentCounterValue = settings[EXAMPLE_COUNTER] ?: 0
    settings[EXAMPLE_COUNTER] = currentCounterValue + 1
  }
}

2.Proto DataStore

• 在build.gradle(:app)添加如下设置

plugins {
    id "com.google.protobuf" version "0.8.12"
}
android{
    sourceSets {
        main {
            proto {
                // proto 文件默认路径是 src/main/proto
                // 可以通过 srcDir 修改 proto 文件的位置
                srcDir 'src/main/proto'
            }
        }
    }
}
dependencies{
    implementation "androidx.datastore:datastore-core:1.0.0"
    implementation "com.google.protobuf:protobuf-javalite:3.10.0"
}
protobuf {
    protoc {
        artifact = "com.google.protobuf:protoc:3.10.0"
    }

    // Generates the java Protobuf-lite code for the Protobufs in this project. See
    // https://github.com/google/protobuf-gradle-plugin#customizing-protobuf-compilation
    // for more information.
    generateProtoTasks {
        all().each { task ->
            task.builtins {
                java {
                    option 'lite'
                }
            }
        }
    }
    // 默认生成目录 $buildDir/generated/source/proto 通过 generatedFilesBaseDir 改变生成位置
    // generatedFilesBaseDir = "$projectDir/src/main"
}

• Define a schema

在src/main/proto/创建一个.proto文件内容如下：

syntax = "proto3";
//包名+文件名
option java_package = "com.example.application";
option java_multiple_files = true;

message Settings {
  int32 example_counter = 1;
}

• Create a Proto DataStore

//定义proto类的序列化器
object SettingsSerializer : Serializer<Settings> {
  override val defaultValue: Settings = Settings.getDefaultInstance()

  override suspend fun readFrom(input: InputStream): Settings {
    try {
      return Settings.parseFrom(input)
    } catch (exception: InvalidProtocolBufferException) {
      throw CorruptionException("Cannot read proto.", exception)
    }
  }

  override suspend fun writeTo(
    t: Settings,
    output: OutputStream) = t.writeTo(output)
}
//定义datastore对象
//The filename parameter tells DataStore which file to use to store the data
val Context.settingsDataStore: DataStore<Settings> by dataStore(
  fileName = "settings.pb",
  serializer = SettingsSerializer
)

• Read from a Proto DataStore

val exampleCounterFlow: Flow<Int> = context.settingsDataStore.data
  .map { settings ->
    // The exampleCounter property is generated from the proto schema.
    settings.exampleCounter
  }

• Write to a Proto DataStore

suspend fun incrementCounter() {
  context.settingsDataStore.updateData { currentSettings ->
    currentSettings.toBuilder()
      .setExampleCounter(currentSettings.exampleCounter + 1)
      .build()
    }
}

Migrate from SharedPreferences to DataStore

val dataStore: DataStore<Preferences> = context.createDataStore(
    name = "settings",
    migrations = listOf(SharedPreferencesMigration(context, "settings_preferences"))
)

SharedPreferences vs DataStore

Room vs DataStore

If you have a need for partial updates, referential integrity, or support for large/complex datasets, you should consider using Room instead of DataStore. DataStore is ideal for small, simple datasets and does not support partial updates or referential integrity.

https://android-developers.googleblog.com/2020/09/prefer-storing-data-with-jetpack.html

Blogs

• Prefer Storing Data with Jetpack DataStore

相关学习资料

• Android Jetpack DataStore