DataStore
Jetpack DataStore 是一种数据存储解决方案，让您可以使用 协议缓冲区存储键值对或类型化对象
Preferences DataStore 可用于替代 SharedPreferences，其是线程安全的
需要注意：
- 请勿在同一进程中为给定文件创建多个 DataStore 实例
- DataStore 的通用类型必须不可变
- 请勿对同一文件混用 SingleProcessDataStore 和 MultiProcessDataStore
依赖
dependencies {
// Preferences DataStore (SharedPreferences like APIs)
implementation "androidx.datastore:datastore-preferences:1.2.1"
// Alternatively - without an Android dependency.
implementation "androidx.datastore:datastore-preferences-core:1.2.1"
// optional - RxJava3 support
implementation "androidx.datastore:datastore-preferences-rxjava3:1.2.1"
// Typed DataStore for custom data objects (for example, using Proto or JSON).
implementation "androidx.datastore:datastore:1.2.1"
// Alternatively - without an Android dependency.
implementation "androidx.datastore:datastore-core:1.2.1"
// optional - RxJava3 support
implementation "androidx.datastore:datastore-rxjava3:1.2.1"
// RxAndroid: 提供 AndroidSchedulers.mainThread()
implementation "io.reactivex.rxjava3:rxandroid:3.0.2"
implementation "io.reactivex.rxjava3:rxjava:3.1.8"
// Gson：用于 JSON DataStore 的序列化/反序列化
implementation "com.google.code.gson:gson:2.10.1"
// 协程 RxJava3 桥接：让 suspend 函数和 Flow 能转成 Single/Flowable
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-rx3:1.7.3"
// Lifecycle: ViewModel + LiveData + 把 RxJava Publisher 适配成 LiveData
def lifecycle_version = "2.7.0"
implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
implementation "androidx.lifecycle:lifecycle-reactivestreams:$lifecycle_version"
}Preferences DataStore
MyApplication
java
public class MyApplication extends Application {
private static MyApplication instance;
/**
* 进程内单例的 DataStore.放在 Application 中持有，整个 App 生命周期复用，不要 dispose。
* /data/data/com.example.demo1/files/datastore/settings.preferences_pb
*/
private static RxDataStore<Preferences> settingsDataStore;
@Override
public void onCreate() {
super.onCreate();
instance = this;
settingsDataStore = new RxPreferenceDataStoreBuilder(this, "settings").build();
}
public static Context getContext() {
return instance;
}
public static RxDataStore<Preferences> getSettingsDataStore() {
return settingsDataStore;
}
}SettingsRepository
public class SettingsRepository {
private static volatile SettingsRepository INSTANCE;
public static SettingsRepository getInstance() {
if (INSTANCE == null) {
synchronized (SettingsRepository.class) {
if (INSTANCE == null) {
INSTANCE = new SettingsRepository(MyApplication.getSettingsDataStore());
}
}
}
return INSTANCE;
}
// key 集中维护，public 让 ViewModel 引用；新增字段只在这加一行
public static final Preferences.Key<Integer> KEY_COUNTER_A = PreferencesKeys.intKey("counter_a");
public static final Preferences.Key<Integer> KEY_COUNTER_B = PreferencesKeys.intKey("counter_b");
private final RxDataStore<Preferences> dataStore;
private SettingsRepository(RxDataStore<Preferences> dataStore) {
this.dataStore = dataStore;
}
/**
* 通用读：调用方用 mapper 把整份 Preferences 映射成自己关心的 T。
* 内部已包成去重（distinctUntilChanged），避免 UI 层收到重复数据。
*/
public <T> Flowable<T> observeChanged(Function<Preferences, T> mapper) {
return dataStore.data()
.map(mapper)
.distinctUntilChanged()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
/**
* 通用读：调用方用 mapper 把整份 Preferences 映射成自己关心的 T。
*/
public <T> Flowable<T> observe(Function<Preferences, T> mapper) {
return dataStore.data()
.map(mapper)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
/**
* 整体快照流，调试日志用。
*/
public Flowable<Preferences> observeAll() {
return observeChanged(prefs -> prefs);
}
/**
* 通用写：调用方用 action 对 MutablePreferences 做任意修改。
* 内部已包成原子事务（DataStore 的 updateDataAsync 语义）。
*/
public Single<Preferences> update(Consumer<MutablePreferences> action) {
return dataStore.updateDataAsync(prefsIn -> {
MutablePreferences m = prefsIn.toMutablePreferences();
try {
action.accept(m);
} catch (Throwable t) {
return Single.error(t);
}
return Single.just(m);
});
}
}SettingsViewModel
java
public class SettingsViewModel extends ViewModel {
private static final String TAG = "DataStoreDemo";
private final SettingsRepository repo = SettingsRepository.getInstance();
private final CompositeDisposable disposables = new CompositeDisposable();
// 读：用 mapper 选取自己关心的字段
private final LiveData<Integer> counterA = LiveDataReactiveStreams.fromPublisher(
repo.observeChanged(prefs -> getOrZero(prefs, SettingsRepository.KEY_COUNTER_A)));
private final LiveData<Integer> counterB = LiveDataReactiveStreams.fromPublisher(
repo.observeChanged(prefs -> getOrZero(prefs, SettingsRepository.KEY_COUNTER_B)));
private final LiveData<Preferences> allEntries =
LiveDataReactiveStreams.fromPublisher(repo.observeAll());
public LiveData<Integer> getCounterA() {
return counterA;
}
public LiveData<Integer> getCounterB() {
return counterB;
}
public LiveData<Preferences> getAllEntries() {
return allEntries;
}
// 写：用 Consumer 描述要做的修改
public void incA() {
disposables.add(
repo.update(m -> {
Integer cur = m.get(SettingsRepository.KEY_COUNTER_A);
m.set(SettingsRepository.KEY_COUNTER_A, (cur == null ? 0 : cur) + 1);
}).subscribe(
p -> Log.d(TAG, "inc A ok"),
e -> Log.e(TAG, "inc A err", e)
));
}
public void incB() {
disposables.add(
repo.update(m -> {
Integer cur = m.get(SettingsRepository.KEY_COUNTER_B);
m.set(SettingsRepository.KEY_COUNTER_B, (cur == null ? 0 : cur) + 1);
}).subscribe(
p -> Log.d(TAG, "inc B ok"),
e -> Log.e(TAG, "inc B err", e)
));
}
public void reset() {
disposables.add(
repo.update(m -> {
m.set(SettingsRepository.KEY_COUNTER_A, 0);
m.set(SettingsRepository.KEY_COUNTER_B, 0);
}).subscribe(
p -> Log.d(TAG, "reset ok"),
e -> Log.e(TAG, "reset err", e)
));
}
private static int getOrZero(Preferences prefs, Preferences.Key<Integer> key) {
Integer v = prefs.get(key);
return v == null ? 0 : v;
}
@Override
protected void onCleared() {
super.onCleared();
disposables.clear();
}
}MainActivity
java
public class MainActivity extends AppCompatActivity {
private static final String TAG = "DataStoreDemo";
private TextView tvCounterA;
private TextView tvCounterB;
private Button mBtnInc;
private Button mBtnIncB;
private Button mBtnReset;
private SettingsViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initViewModel();
initListener();
}
private void initView() {
tvCounterA = findViewById(R.id.tv_counterA);
tvCounterB = findViewById(R.id.tv_counter_b);
mBtnInc = findViewById(R.id.btn_inc);
mBtnIncB = findViewById(R.id.btn_inc_b);
mBtnReset = findViewById(R.id.btn_reset);
}
private void initViewModel() {
viewModel = new ViewModelProvider(this).get(SettingsViewModel.class);
viewModel.getCounterA().observe(this, value ->
tvCounterA.setText("A=" + value));
viewModel.getCounterB().observe(this, value ->
tvCounterB.setText("B=" + value));
viewModel.getAllEntries().observe(this, this::logAllEntries);
}
private void initListener() {
mBtnInc.setOnClickListener(v -> viewModel.incA());
mBtnIncB.setOnClickListener(v -> viewModel.incB());
mBtnReset.setOnClickListener(v -> viewModel.reset());
}
private void logAllEntries(Preferences prefs) {
Log.d(TAG, "all entries = " + prefs.asMap());
}
}activity_main.xml
xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/page_list_container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv_counterA"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toTopOf="@id/tv_counter_b"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<TextView
android:id="@+id/tv_counter_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/tv_counterA"
app:layout_constraintBottom_toTopOf="@id/btn_inc"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<Button
android:id="@+id/btn_inc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="A +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toBottomOf="@id/tv_counter_b"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toStartOf="@id/btn_inc_b" />
<Button
android:id="@+id/btn_inc_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="B +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc"
app:layout_constraintEnd_toStartOf="@id/btn_reset" />
<Button
android:id="@+id/btn_reset"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="重置"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc_b"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>查看数据
从以下路径取出文件
/data/data/com.example.demo1/files/datastore/settings.preferences_pb安装protobuf
brew install protobuf进入如下网站搜索datastore-preferences-proto
https://github.com/androidx/androidx/tree/androidx-main找到preferences.proto
根据package通过如下命令解析
protoc --decode=androidx.datastore.testing.PreferenceMap \
preferences.proto \
< settings.preferences_pb解析结果如下
preferences {
key: "counter_a"
value {
integer: 1
}
}
preferences {
key: "counter_b"
value {
integer: 1
}
}JSON DataStore
Settings
java
public class Settings {
/**
* 使用final 字段 + withXxx 方法，保证不可变性。
*/
public final int counterA;
public final int counterB;
/**
* 无参构造：Gson 反序列化时需要；默认值全为 0。
*/
public Settings() {
this(0, 0);
}
public Settings(int counterA, int counterB) {
this.counterA = counterA;
this.counterB = counterB;
}
public Settings withCounterA(int value) {
return new Settings(value, counterB);
}
public Settings withCounterB(int value) {
return new Settings(counterA, value);
}
@NonNull
@Override
public String toString() {
return "Settings{counterA=" + counterA + ", counterB=" + counterB + "}";
}
}SettingsSerializer.kt
kotlin
object SettingsSerializer : Serializer<Settings> {
private val gson = Gson()
override val defaultValue: Settings = Settings()
override suspend fun readFrom(input: InputStream): Settings {
return try {
InputStreamReader(input, StandardCharsets.UTF_8).use { reader ->
gson.fromJson(reader, Settings::class.java) ?: defaultValue
}
} catch (e: Exception) {
throw CorruptionException("settings.json corrupted", e)
}
}
override suspend fun writeTo(t: Settings, output: OutputStream) {
OutputStreamWriter(output, StandardCharsets.UTF_8).use { writer ->
gson.toJson(t, writer)
}
}
}SettingsRepository
java
public class SettingsRepository {
private static volatile SettingsRepository INSTANCE;
public static SettingsRepository getInstance() {
if (INSTANCE == null) {
synchronized (SettingsRepository.class) {
if (INSTANCE == null) {
INSTANCE = new SettingsRepository();
}
}
}
return INSTANCE;
}
private final RxDataStore<Settings> dataStore;
private SettingsRepository() {
// SettingsSerializer 是 Kotlin object，Java 里通过 .INSTANCE 引用
dataStore = new RxDataStoreBuilder<>(
MyApplication.getContext(), "settings.json", SettingsSerializer.INSTANCE
).build();
}
/**
* 通用读：调用方用 mapper 从整份 Settings 里提取关心的字段 T。
* 已包含 distinctUntilChanged 去重。
*/
public <T> Flowable<T> observeChanged(Function<Settings, T> mapper) {
return dataStore.data()
.map(mapper)
.distinctUntilChanged()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
public <T> Flowable<T> observe(Function<Settings, T> mapper) {
return dataStore.data()
.map(mapper)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
/**
* 整体快照流，调试日志用。
*/
public Flowable<Settings> observeAll() {
return observeChanged(settings -> settings);
}
/**
* 通用写：调用方传入 updater，接收当前 Settings，返回新的 Settings。
* 注意与 Preferences DataStore 的区别：
* - Preferences：{@code Consumer<MutablePreferences>}（修改 mutable 对象，无返回值）
* - JSON DataStore：{@code Function<Settings, Settings>}（不可变，返回新对象）
*/
public Single<Settings> update(Function<Settings, Settings> updater) {
return dataStore.updateDataAsync(current -> {
try {
return Single.just(updater.apply(current));
} catch (Throwable t) {
return Single.error(t);
}
});
}
}SettingsViewModel
java
public class SettingsViewModel extends ViewModel {
private static final String TAG = "JsonDataStoreDemo";
private final SettingsRepository repo = SettingsRepository.getInstance();
private final CompositeDisposable disposables = new CompositeDisposable();
private final LiveData<Integer> counterA =
LiveDataReactiveStreams.fromPublisher(repo.observeChanged(settings -> settings.counterA));
private final LiveData<Integer> counterB =
LiveDataReactiveStreams.fromPublisher(repo.observeChanged(settings -> settings.counterB));
private final LiveData<Settings> allEntries =
LiveDataReactiveStreams.fromPublisher(repo.observeAll());
public LiveData<Integer> getCounterA() {
return counterA;
}
public LiveData<Integer> getCounterB() {
return counterB;
}
public LiveData<Settings> getAllEntries() {
return allEntries;
}
// 写：updater 接收当前 Settings，返回新的 Settings（不可变拷贝）
public void incA() {
disposables.add(
repo.update(s -> s.withCounterA(s.counterA + 1))
.subscribe(
s -> Log.d(TAG, "inc A ok: " + s),
e -> Log.e(TAG, "inc A err", e)
)
);
}
public void incB() {
disposables.add(
repo.update(s -> s.withCounterB(s.counterB + 1))
.subscribe(
s -> Log.d(TAG, "inc B ok: " + s),
e -> Log.e(TAG, "inc B err", e)
)
);
}
public void reset() {
disposables.add(
repo.update(s -> new Settings())
.subscribe(
s -> Log.d(TAG, "reset ok: " + s),
e -> Log.e(TAG, "reset err", e)
)
);
}
@Override
protected void onCleared() {
super.onCleared();
disposables.clear();
}
}MainActivity
java
public class MainActivity extends AppCompatActivity {
private static final String TAG = "DataStoreDemo";
private TextView tvCounterA;
private TextView tvCounterB;
private Button mBtnInc;
private Button mBtnIncB;
private Button mBtnReset;
private SettingsViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initViewModel();
initListener();
}
private void initView() {
tvCounterA = findViewById(R.id.tv_counterA);
tvCounterB = findViewById(R.id.tv_counter_b);
mBtnInc = findViewById(R.id.btn_inc);
mBtnIncB = findViewById(R.id.btn_inc_b);
mBtnReset = findViewById(R.id.btn_reset);
}
private void initViewModel() {
viewModel = new ViewModelProvider(this).get(SettingsViewModel.class);
viewModel.getCounterA().observe(this, value ->
tvCounterA.setText("A=" + value));
viewModel.getCounterB().observe(this, value ->
tvCounterB.setText("B=" + value));
viewModel.getAllEntries().observe(this, this::logAllEntries);
}
private void initListener() {
mBtnInc.setOnClickListener(v -> viewModel.incA());
mBtnIncB.setOnClickListener(v -> viewModel.incB());
mBtnReset.setOnClickListener(v -> viewModel.reset());
}
private void logAllEntries(Settings settings) {
Log.d(TAG, "all entries = " + settings);
}
}activity_main.xml
xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/page_list_container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv_counterA"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toTopOf="@id/tv_counter_b"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<TextView
android:id="@+id/tv_counter_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/tv_counterA"
app:layout_constraintBottom_toTopOf="@id/btn_inc"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<Button
android:id="@+id/btn_inc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="A +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toBottomOf="@id/tv_counter_b"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toStartOf="@id/btn_inc_b" />
<Button
android:id="@+id/btn_inc_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="B +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc"
app:layout_constraintEnd_toStartOf="@id/btn_reset" />
<Button
android:id="@+id/btn_reset"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="重置"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc_b"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>查看数据
从以下路径取出文件
/data/data/com.example.demo1/files/datastore/settings.jsonjson格式可直接打开，结果如下
{"counterA":0,"counterB":0}多进程代码中使用 DataStore
DataStore提供多进程同步
- 读取仅返回已持久存储到磁盘的数据。
- 写后读一致性。
- 写入会序列化。
- 写入绝不会阻塞读取。
MyApplication
java
public class MyApplication extends Application {
private static MyApplication instance;
@Override
public void onCreate() {
super.onCreate();
instance = this;
// JSON DataStore（多进程）：每个进程的 Application.onCreate() 各自调一次 init，
// 两个进程指向同一个 settings.json 文件，由文件锁保证跨进程一致性。
MultiProcessSettingsDataStore.INSTANCE.init(this);
}
public static Context getContext() {
return instance;
}
}Settings
java
public class Settings {
/**
* 使用final 字段 + withXxx 方法，保证不可变性。
*/
public final int counterA;
public final int counterB;
/**
* 无参构造：Gson 反序列化时需要；默认值全为 0。
*/
public Settings() {
this(0, 0);
}
public Settings(int counterA, int counterB) {
this.counterA = counterA;
this.counterB = counterB;
}
public Settings withCounterA(int value) {
return new Settings(value, counterB);
}
public Settings withCounterB(int value) {
return new Settings(counterA, value);
}
@NonNull
@Override
public String toString() {
return "Settings{counterA=" + counterA + ", counterB=" + counterB + "}";
}
}SettingsSerializer.kt
java
object SettingsSerializer : Serializer<Settings> {
private val gson = Gson()
override val defaultValue: Settings = Settings()
override suspend fun readFrom(input: InputStream): Settings {
return try {
InputStreamReader(input, StandardCharsets.UTF_8).use { reader ->
gson.fromJson(reader, Settings::class.java) ?: defaultValue
}
} catch (e: Exception) {
throw CorruptionException("settings.json corrupted", e)
}
}
override suspend fun writeTo(t: Settings, output: OutputStream) {
OutputStreamWriter(output, StandardCharsets.UTF_8).use { writer ->
gson.toJson(t, writer)
}
}
}SettingsRepository
java
public class SettingsRepository {
private static volatile SettingsRepository INSTANCE;
public static SettingsRepository getInstance() {
if (INSTANCE == null) {
synchronized (SettingsRepository.class) {
if (INSTANCE == null) {
INSTANCE = new SettingsRepository();
}
}
}
return INSTANCE;
}
private SettingsRepository() {
// MultiProcessSettingsDataStore 已在 MyApplication.onCreate() 中 init，这里直接使用
}
// ---------- 读 ----------
/**
* 通用读：mapper 从 Settings 里提取关心的字段 T，已包含 distinctUntilChanged。
* 任意进程写入后，此 Flowable 都会收到通知。
*/
public <T> Flowable<T> observeChanged(Function<Settings, T> mapper) {
return MultiProcessSettingsDataStore.INSTANCE.data()
.map(mapper)
.distinctUntilChanged()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
/** 整体快照流，调试日志用。 */
public Flowable<Settings> observeAll() {
return observeChanged(settings -> settings);
}
// ---------- 写 ----------
/**
* 通用写：updater 接收当前 Settings，返回新 Settings。
* 底层使用文件锁，跨进程写操作串行，不会丢数据。
*/
public Single<Settings> update(Function<Settings, Settings> updater) {
return MultiProcessSettingsDataStore.INSTANCE.update(updater);
}
}SettingsViewModel
java
public class SettingsViewModel extends ViewModel {
private static final String TAG = "JsonDataStoreDemo";
private final SettingsRepository repo = SettingsRepository.getInstance();
private final CompositeDisposable disposables = new CompositeDisposable();
private final LiveData<Integer> counterA =
LiveDataReactiveStreams.fromPublisher(repo.observeChanged(settings -> settings.counterA));
private final LiveData<Integer> counterB =
LiveDataReactiveStreams.fromPublisher(repo.observeChanged(settings -> settings.counterB));
private final LiveData<Settings> allEntries =
LiveDataReactiveStreams.fromPublisher(repo.observeAll());
public LiveData<Integer> getCounterA() {
return counterA;
}
public LiveData<Integer> getCounterB() {
return counterB;
}
public LiveData<Settings> getAllEntries() {
return allEntries;
}
// 写：updater 接收当前 Settings，返回新的 Settings（不可变拷贝）
public void incA() {
disposables.add(
repo.update(s -> s.withCounterA(s.counterA + 1))
.subscribe(
s -> Log.d(TAG, "inc A ok: " + s),
e -> Log.e(TAG, "inc A err", e)
)
);
}
public void incB() {
disposables.add(
repo.update(s -> s.withCounterB(s.counterB + 1))
.subscribe(
s -> Log.d(TAG, "inc B ok: " + s),
e -> Log.e(TAG, "inc B err", e)
)
);
}
public void reset() {
disposables.add(
repo.update(s -> new Settings())
.subscribe(
s -> Log.d(TAG, "reset ok: " + s),
e -> Log.e(TAG, "reset err", e)
)
);
}
@Override
protected void onCleared() {
super.onCleared();
disposables.clear();
}
}MultiProcessSettingsDataStore.kt
kotlin
object MultiProcessSettingsDataStore {
// "lateinit var" 表示延迟初始化的变量（先声明，后赋值）
// 相当于 Java 的 private DataStore<Settings> dataStore;
// "private" 只在本文件内可见
private lateinit var dataStore: DataStore<Settings>
/**
* 初始化，在 MyApplication.onCreate() 中调用。
* 每个进程各自调一次，但两个进程指向同一个 settings.json 文件。
*/
// "fun" 是 Kotlin 的方法声明，相当于 Java 的 void/返回值类型 方法名()
fun init(context: Context) {
// "::dataStore.isInitialized" 判断 lateinit 变量是否已赋值，避免重复初始化
// 相当于 Java 的 if (dataStore != null) return;
if (::dataStore.isInitialized) return
// MultiProcessDataStoreFactory.create() 创建支持跨进程的 DataStore
// 相当于 Java 的 new RxDataStoreBuilder<>(...).build()，但支持文件锁
dataStore = MultiProcessDataStoreFactory.create(
serializer = SettingsSerializer, // 序列化器，告诉 DataStore 如何读写 Settings 对象
produceFile = {
// 这是一个 lambda（匿名函数），返回文件路径
// 相当于 Java 的 () -> new File(...)
// 两个进程必须返回同一个路径，才能共享数据
File("${context.applicationContext.filesDir}/datastore/settings.json")
// "${...}" 是 Kotlin 的字符串模板，相当于 Java 的 + 拼接
},
corruptionHandler = ReplaceFileCorruptionHandler { Settings(1,1) }
)
}
/**
* 读：把 Kotlin 的 Flow<Settings> 转成 Java 能用的 Flowable<Settings>。
* 任意进程写入后，其他进程的订阅者都会收到通知。
*/
fun data(): Flowable<Settings> =
// rxFlowable { } 把协程 block 转成 Flowable，来自 kotlinx-coroutines-rx3 库
rxFlowable(Dispatchers.IO) {
// dataStore.data 是 Flow<Settings>（Kotlin 的数据流，类似 RxJava 的 Flowable）
// .collect { } 是订阅操作，相当于 RxJava 的 .subscribe(value -> ...)
// send(it) 把每次收到的 Settings 发射出去给 Flowable 的订阅者
// "it" 是 Kotlin lambda 只有一个参数时的默认名字，相当于 Java 的 s -> send(s)
dataStore.data.collect { send(it) }
}
/**
* 写：接收 Java 的 RxFunction，底层调用 suspend updateData，包装成 Single。
*/
// "Function<Settings, Settings>" 是 RxJava3 的函数接口
// 用 RxJava 的 Function 而不是 Kotlin 的 (Settings) -> Settings，
// 是为了让 Java 调用方可以直接传 lambda，不需要感知 Kotlin 类型
fun update(transform: Function<Settings, Settings>): Single<Settings> =
// rxSingle { } 把一个 suspend 操作转成 Single，来自 kotlinx-coroutines-rx3 库
rxSingle(Dispatchers.IO) {
// dataStore.updateData 是 suspend 函数（只能在协程里调用）
// 在文件锁内原子执行：先读 → 执行 transform → 写盘
// transform.apply(it) 调用 Java 的 Function 接口方法，相当于 Java 的 transform.apply(current)
dataStore.updateData { transform.apply(it) }
}
}AndroidManifest.xml
xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<application
android:name=".MyApplication"
android:allowBackup="true"
android:dataExtractionRules="@xml/data_extraction_rules"
android:fullBackupContent="@xml/backup_rules"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/Theme.Demo1"
tools:targetApi="31">
<activity
android:name=".datastore.MainActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!--
android:process=":b_process" 让 ActivityB 运行在独立进程。
前缀 ":" 表示这是 App 私有进程，完整名为 com.example.demo1:b_process。
该进程有自己的 MyApplication.onCreate()，会重新初始化 MultiProcessSettingsDataStore，
但指向同一个 settings.json 文件，由文件锁保证跨进程数据一致性。
-->
<activity
android:name=".datastore.json.ActivityB"
android:exported="false"
android:process=":b_process" />
</application>
</manifest>MainActivity
java
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private TextView tvCounterA;
private TextView tvCounterB;
private Button mBtnInc;
private Button mBtnIncB;
private Button mBtnReset;
private Button mBtnGoB;
private Button mBtnCorrupt;
private SettingsViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
initView();
initViewModel();
initListener();
}
private void initView() {
tvCounterA = findViewById(R.id.tv_counterA);
tvCounterB = findViewById(R.id.tv_counter_b);
mBtnInc = findViewById(R.id.btn_inc);
mBtnIncB = findViewById(R.id.btn_inc_b);
mBtnReset = findViewById(R.id.btn_reset);
mBtnGoB = findViewById(R.id.btn_go_b);
mBtnCorrupt = findViewById(R.id.btn_corrupt);
}
private void initViewModel() {
viewModel = new ViewModelProvider(this).get(SettingsViewModel.class);
viewModel.getCounterA().observe(this, value ->
tvCounterA.setText("A=" + value));
viewModel.getCounterB().observe(this, value ->
tvCounterB.setText("B=" + value));
viewModel.getAllEntries().observe(this, this::logAllEntries);
}
private void initListener() {
mBtnInc.setOnClickListener(v -> viewModel.incA());
mBtnIncB.setOnClickListener(v -> viewModel.incB());
mBtnReset.setOnClickListener(v -> viewModel.reset());
mBtnGoB.setOnClickListener(v ->
startActivity(new Intent(this, ActivityB.class)));
mBtnCorrupt.setOnClickListener(v -> corruptAndRestart());
}
/**
* 写入非法 JSON 并杀进程，下次启动会抛异常CorruptionException，然后通过 ReplaceFileCorruptionHandler 修复文件
*/
private void corruptAndRestart() {
File f = new File(getFilesDir(), "datastore/settings.json");
try (FileOutputStream fos = new FileOutputStream(f)) {
fos.write("not a json".getBytes());
Log.d(TAG, "corrupted: " + f.getAbsolutePath());
Toast.makeText(this, "已破坏文件，进程将重启", Toast.LENGTH_SHORT).show();
} catch (IOException e) {
Log.e(TAG, "corrupt failed", e);
return;
}
// 延迟一下，让 Toast 有机会显示
mBtnCorrupt.postDelayed(
() -> android.os.Process.killProcess(android.os.Process.myPid()),
500);
}
private void logAllEntries(Settings settings) {
Log.d(TAG, "all entries = " + settings);
}
}activity_main.xml
xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/page_list_container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv_counterA"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toTopOf="@id/tv_counter_b"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<TextView
android:id="@+id/tv_counter_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/tv_counterA"
app:layout_constraintBottom_toTopOf="@id/btn_inc"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<Button
android:id="@+id/btn_inc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="A +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toBottomOf="@id/tv_counter_b"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toStartOf="@id/btn_inc_b" />
<Button
android:id="@+id/btn_inc_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="B +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc"
app:layout_constraintEnd_toStartOf="@id/btn_reset" />
<Button
android:id="@+id/btn_reset"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="重置"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc_b"
app:layout_constraintEnd_toEndOf="parent" />
<Button
android:id="@+id/btn_go_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="跳到进程B"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<Button
android:id="@+id/btn_corrupt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="破坏文件并重启"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/btn_go_b"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>ActivityB
java
public class ActivityB extends AppCompatActivity {
private static final String TAG = "ActivityB";
private TextView tvCounterA;
private TextView tvCounterB;
private SettingsViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_b);
tvCounterA = findViewById(R.id.tv_counterA);
tvCounterB = findViewById(R.id.tv_counter_b);
Button btnInc = findViewById(R.id.btn_inc);
Button btnIncB = findViewById(R.id.btn_inc_b);
Button btnReset = findViewById(R.id.btn_reset);
// SettingsViewModel 和 SettingsRepository 与主进程用同一套代码，
// 但这是 :b_process 里全新的实例，通过文件锁与主进程协调
viewModel = new ViewModelProvider(this).get(SettingsViewModel.class);
viewModel.getCounterA().observe(this, value -> {
tvCounterA.setText("A = " + value);
Log.d(TAG, "counterA updated: " + value);
});
viewModel.getCounterB().observe(this, value -> {
tvCounterB.setText("B = " + value);
Log.d(TAG, "counterB updated: " + value);
});
viewModel.getAllEntries().observe(this, s ->
Log.d(TAG, "all entries = " + s));
btnInc.setOnClickListener(v -> viewModel.incA());
btnIncB.setOnClickListener(v -> viewModel.incB());
btnReset.setOnClickListener(v -> viewModel.reset());
}
}activity_b.xml
xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv_process_tag"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Process B"
android:textSize="14sp"
android:textColor="#FF5722"
android:layout_marginTop="32dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<TextView
android:id="@+id/tv_counterA"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/tv_process_tag"
app:layout_constraintBottom_toTopOf="@id/tv_counter_b"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<TextView
android:id="@+id/tv_counter_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="24sp"
android:layout_marginTop="16dp"
app:layout_constraintTop_toBottomOf="@id/tv_counterA"
app:layout_constraintBottom_toTopOf="@id/btn_inc"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<Button
android:id="@+id/btn_inc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="A +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toBottomOf="@id/tv_counter_b"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toStartOf="@id/btn_inc_b" />
<Button
android:id="@+id/btn_inc_b"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="B +1"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc"
app:layout_constraintEnd_toStartOf="@id/btn_reset" />
<Button
android:id="@+id/btn_reset"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="重置"
app:layout_constraintTop_toTopOf="@id/btn_inc"
app:layout_constraintBottom_toBottomOf="@id/btn_inc"
app:layout_constraintStart_toEndOf="@id/btn_inc_b"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>