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Merge pull request #60 from PureSwift/feature/appstorage
Add @AppStorage
2 parents 4cdc464 + 81bc940 commit db5cc6f

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Lines changed: 256 additions & 1 deletion

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‎AndroidSwiftUICore/Sources/AndroidSwiftUICore/AppStorage.swift‎

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//
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// AppStorage.swift
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// AndroidSwiftUICore
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//
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// Values that outlive the process. The core owns no platform APIs, so the
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// backing store is a protocol the host installs — a JSON file under the app's
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// files directory on Android, an in-memory store in tests. Reads and writes
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// go through the same `StateBox` machinery `@State` uses, so a change marks the
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// view dirty exactly like any other state write.
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//
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import Foundation
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/// Where `@AppStorage` values are kept between launches.
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public protocol AppStorageBackend: AnyObject {
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func value(forKey key: String) -> Any?
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func set(_ value: Any?, forKey key: String)
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}
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/// The process-wide store. Defaults to memory so the core works — and tests —
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/// without a host; `ViewHost` installs a persistent one on Android.
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public enum AppStorageStore {
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nonisolated(unsafe) public static var backend: AppStorageBackend = InMemoryAppStorage()
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internal static func read<Value>(_ key: String, as type: Value.Type) -> Value? {
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backend.value(forKey: key) as? Value
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}
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internal static func write(_ value: Any?, _ key: String) {
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backend.set(value, forKey: key)
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}
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}
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public final class InMemoryAppStorage: AppStorageBackend {
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private var values: [String: Any] = [:]
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public init() {}
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public func value(forKey key: String) -> Any? { values[key] }
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public func set(_ value: Any?, forKey key: String) { values[key] = value }
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}
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/// A JSON file on disk. Small by design: `@AppStorage` is for preferences, and
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/// rewriting the whole file per write keeps it consistent without a database.
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public final class FileAppStorage: AppStorageBackend {
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private let url: URL
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private var values: [String: Any]
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public init(directory: String, name: String = "app-storage.json") {
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self.url = URL(fileURLWithPath: directory).appendingPathComponent(name)
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if let data = try? Data(contentsOf: url),
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let decoded = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
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self.values = decoded
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} else {
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self.values = [:]
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}
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}
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public func value(forKey key: String) -> Any? { values[key] }
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public func set(_ value: Any?, forKey key: String) {
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if let value { values[key] = value } else { values.removeValue(forKey: key) }
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guard let data = try? JSONSerialization.data(withJSONObject: values) else { return }
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try? data.write(to: url, options: .atomic)
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}
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}
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// MARK: - The wrapper
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/// A value persisted under `key`, readable and writable like `@State`.
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@propertyWrapper
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public struct AppStorage<Value>: DynamicProperty {
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internal let box: StateBox<Value>
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internal let key: String
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private init(key: String, defaultValue: Value) {
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self.key = key
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// seed from the store so the first read already reflects what was saved
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self.box = StateBox(AppStorageStore.read(key, as: Value.self) ?? defaultValue)
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}
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public var wrappedValue: Value {
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get { box.value }
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nonmutating set {
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box.value = newValue
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AppStorageStore.write(newValue, key)
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}
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}
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public var projectedValue: Binding<Value> {
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let key = self.key
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let box = self.box
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return Binding(
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get: { box.value },
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set: { box.value = $0; AppStorageStore.write($0, key) }
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)
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}
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}
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// Only the types a preferences store can round-trip through JSON.
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public extension AppStorage where Value == Bool {
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init(wrappedValue: Value, _ key: String) { self.init(key: key, defaultValue: wrappedValue) }
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}
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public extension AppStorage where Value == Int {
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init(wrappedValue: Value, _ key: String) { self.init(key: key, defaultValue: wrappedValue) }
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}
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public extension AppStorage where Value == Double {
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init(wrappedValue: Value, _ key: String) { self.init(key: key, defaultValue: wrappedValue) }
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}
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public extension AppStorage where Value == String {
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init(wrappedValue: Value, _ key: String) { self.init(key: key, defaultValue: wrappedValue) }
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}
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extension AppStorage: _StatePropertyReflectable {
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public var _box: AnyObject { box }
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}

‎AndroidSwiftUICore/Tests/AndroidSwiftUICoreTests/ControlTests.swift‎

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case .int(let id)? = mod.args["onChange"] else { return nil }
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return Int64(id)
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}
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@Suite("AppStorage")
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struct AppStorageTests {
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@Test("A stored value survives a fresh wrapper, as it would a relaunch")
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func persistsAcrossWrappers() {
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AppStorageStore.backend = InMemoryAppStorage()
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// first "launch": default, then the user changes it
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struct First: View {
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@AppStorage("volume") var volume = 5
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var body: some View { Text("\(volume)") }
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}
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let first = First()
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#expect(first.volume == 5)
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first.volume = 9
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// a fresh wrapper reads what was written, not the default
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struct Second: View {
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@AppStorage("volume") var volume = 5
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var body: some View { Text("\(volume)") }
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}
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#expect(Second().volume == 9)
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}
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@Test("Each supported type round-trips under its own key")
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func supportedTypes() {
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AppStorageStore.backend = InMemoryAppStorage()
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struct Screen: View {
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@AppStorage("on") var on = false
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@AppStorage("count") var count = 0
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@AppStorage("ratio") var ratio = 0.0
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@AppStorage("name") var name = ""
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var body: some View { Text(name) }
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}
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let screen = Screen()
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screen.on = true
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screen.count = 42
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screen.ratio = 0.75
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screen.name = "Coleman"
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#expect(AppStorageStore.read("on", as: Bool.self) == true)
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#expect(AppStorageStore.read("count", as: Int.self) == 42)
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#expect(AppStorageStore.read("ratio", as: Double.self) == 0.75)
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#expect(AppStorageStore.read("name", as: String.self) == "Coleman")
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// keys stay independent
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#expect(Screen().count == 42)
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#expect(Screen().name == "Coleman")
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}
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@Test("The projected binding writes through to the store")
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func bindingWritesThrough() {
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AppStorageStore.backend = InMemoryAppStorage()
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struct Screen: View {
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@AppStorage("nickname") var nickname = ""
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var body: some View { TextField("Name", text: $nickname) }
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}
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let host = ViewHost(Screen())
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let node = host.evaluate()
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guard case .int(let id)? = node.props["onChange"] else {
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Issue.record("missing field callback"); return
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}
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host.callbacks.invokeString(Int64(id), "typed in")
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#expect(AppStorageStore.read("nickname", as: String.self) == "typed in")
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}
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@Test("A file-backed store reloads what a previous instance wrote")
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func fileBackedRoundTrip() throws {
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let directory = NSTemporaryDirectory() + "appstorage-test-\(UInt32.random(in: 0..<100_000))"
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try FileManager.default.createDirectory(atPath: directory, withIntermediateDirectories: true)
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defer { try? FileManager.default.removeItem(atPath: directory) }
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let first = FileAppStorage(directory: directory)
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first.set(7, forKey: "launches")
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first.set("dark", forKey: "theme")
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// a second instance is what the next launch sees
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let second = FileAppStorage(directory: directory)
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#expect(second.value(forKey: "launches") as? Int == 7)
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#expect(second.value(forKey: "theme") as? String == "dark")
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// and removal sticks
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second.set(nil, forKey: "theme")
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#expect(FileAppStorage(directory: directory).value(forKey: "theme") == nil)
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}
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}

‎Demo/App.swiftpm/Sources/AppStoragePlaygrounds.swift‎

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#if canImport(AndroidSwiftUI)
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import AndroidSwiftUI
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#else
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import SwiftUI
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#endif
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struct AppStoragePlayground: View {
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@AppStorage("demo.launches") private var launches = 0
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@AppStorage("demo.nickname") private var nickname = ""
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@AppStorage("demo.notify") private var notify = false
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@AppStorage("demo.volume") private var volume = 0.5
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var body: some View {
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ScrollView {
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VStack(alignment: .leading, spacing: 0) {
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Example("Survives a relaunch") {
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VStack(alignment: .leading, spacing: 8) {
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Text("Counter: \(launches)")
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Text("Kill and reopen the app — it keeps its value.")
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Button("Increment") { launches += 1 }
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Button("Reset") { launches = 0 }
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}
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}
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Example("String") {
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VStack(alignment: .leading, spacing: 8) {
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TextField("Nickname", text: $nickname)
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Text("Stored: \(nickname)")
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}
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}
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Example("Bool") {
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Toggle("Notifications", isOn: $notify)
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}
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Example("Double") {
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VStack(alignment: .leading, spacing: 8) {
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Slider(value: $volume, in: 0...1)
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Text("Volume: \(Int(volume * 100))%")
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}
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}
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}
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}
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.navigationTitle("AppStorage")
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}
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}

‎Demo/App.swiftpm/Sources/Catalog.swift‎

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CatalogEntry(id: "accessibility", title: "Accessibility", screen: AnyCatalogScreen(AccessibilityPlayground())),
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CatalogEntry(id: "state", title: "State", screen: AnyCatalogScreen(StatePlayground())),
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CatalogEntry(id: "preference", title: "Preferences", screen: AnyCatalogScreen(PreferencePlayground())),
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CatalogEntry(id: "appstorage", title: "AppStorage", screen: AnyCatalogScreen(AppStoragePlayground())),
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CatalogEntry(id: "environment", title: "Environment", screen: AnyCatalogScreen(EnvironmentPlayground())),
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CatalogEntry(id: "observable", title: "Observable", screen: AnyCatalogScreen(ObservablePlayground())),
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CatalogEntry(id: "bindable", title: "Bindable", screen: AnyCatalogScreen(BindablePlayground())),

‎Sources/AndroidSwiftUI/MainActivity.swift‎

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public func onCreateSwift(_ savedInstanceState: BaseBundle?) {
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log("\(self).\(#function)")
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MainActivity.shared = self
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// Point @AppStorage at a file in the app's private storage before any
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// view is built, so the first evaluation already reads saved values.
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// The path comes through the existing Context binding — no new bridge.
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if let directory = (self as AndroidContent.Context).getFilesDir()?.getAbsolutePath() {
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AppStorageStore.backend = FileAppStorage(directory: directory)
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} else {
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log("MainActivity: no files directory; @AppStorage stays in memory")
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}
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// start app
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AndroidSwiftUIMain()
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