Add option to save state between app launches

Documentation/Reference/README.md

@@ -71,6 +71,7 @@
 -   [MenuItem](extensions/MenuItem.md)
 -   [MenuItemGroup](extensions/MenuItemGroup.md)
 -   [NativeWidgetPeer](extensions/NativeWidgetPeer.md)
+-   [State](extensions/State.md)
 -   [String](extensions/String.md)
 -   [View](extensions/View.md)
 -   [Widget](extensions/Widget.md)

Documentation/Reference/classes/GTUIApp.md

@@ -9,6 +9,10 @@ The GTUI application.
 
 The handlers which are called when a state changes.
 
+### `appID`
+
+The app's id for the file name for storing the data.
+
 ### `body`
 
 The app's content.

Documentation/Reference/classes/State.Storage.md

@@ -9,6 +9,10 @@ A class storing the value.
 
 The stored value.
 
+### `key`
+
+The storage key.
+
 ## Methods
 ### `init(value:)`
 

Documentation/Reference/extensions/State.md

@@ -0,0 +1,23 @@
+**EXTENSION**
+
+# `State`
+
+## Methods
+### `init(wrappedValue:_:)`
+
+Initialize a property representing a state in the view.
+- Parameters:
+    - key: The unique storage key of the property.
+    - wrappedValue: The wrapped value.
+
+### `checkFile()`
+
+Check whether the settings file exists, and, if not, create it.
+
+### `readValue()`
+
+Update the local value with the value from the file.
+
+### `writeCodableValue()`
+
+Update the value on the file with the local value.

Documentation/Reference/extensions/View.md

@@ -24,6 +24,12 @@ Get a storage.
 
 ### `getModified(modifiers:)`
 
+### `inspectOnAppear(_:)`
+
+Run a function on the widget when it appears for the first time.
+- Parameter closure: The function.
+- Returns: A view.
+
 ### `onAppear(_:)`
 
 Run a function when the view appears for the first time.

Documentation/Reference/structs/State.md

@@ -21,6 +21,10 @@ Get and set the value without updating the views.
 
 The stored value.
 
+### `writeValue`
+
+The function for updating the value in the settings file.
+
 ### `value`
 
 The value with an erased type.
@@ -35,3 +39,13 @@ Initialize a property representing a state in the view.
 ### `updateViews()`
 
 Update all of the views.
+
+### `dirPath()`
+
+Get the settings directory path.
+- Returns: The path.
+
+### `filePath()`
+
+Get the settings file path.
+- Returns: The path.

Sources/Adwaita/Model/Data Flow/State.swift

@@ -39,6 +39,7 @@ public struct State<Value>: StateProtocol {
         }
         nonmutating set {
             content.storage.value = newValue
+            writeValue?()
         }
     }
     // swiftlint:enable force_cast
@@ -46,6 +47,9 @@ public struct State<Value>: StateProtocol {
     /// The stored value.
     public let content: State<Any>.Content
 
+    /// The function for updating the value in the settings file.
+    private var writeValue: (() -> Void)?
+
     /// The value with an erased type.
     public var value: Any {
         get {
@@ -84,6 +88,8 @@ public struct State<Value>: StateProtocol {
 
         /// The stored value.
         public var value: Any
+        /// The storage key.
+        public var key: String?
 
         /// Initialize the storage.
         /// - Parameters:
@@ -101,4 +107,63 @@ public struct State<Value>: StateProtocol {
         }
     }
 
+    /// Get the settings directory path.
+    /// - Returns: The path.
+    private func dirPath() -> String {
+        "\(NSHomeDirectory())/.config/\(GTUIApp.appID)/"
+    }
+
+    /// Get the settings file path.
+    /// - Returns: The path.
+    private func filePath() -> URL {
+        .init(fileURLWithPath: dirPath() + "\(content.storage.key ?? "temporary").json")
+    }
+
+}
+
+extension State where Value: Codable {
+
+    /// Initialize a property representing a state in the view.
+    /// - Parameters:
+    ///     - key: The unique storage key of the property.
+    ///     - wrappedValue: The wrapped value.
+    public init(wrappedValue: Value, _ key: String) {
+        content = .init(storage: .init(value: wrappedValue))
+        content.storage.key = key
+        checkFile()
+        readValue()
+        self.writeValue = writeCodableValue
+    }
+
+    /// Check whether the settings file exists, and, if not, create it.
+    private func checkFile() {
+        let fileManager = FileManager.default
+        if !fileManager.fileExists(atPath: dirPath()) {
+            try? fileManager.createDirectory(
+                at: .init(fileURLWithPath: dirPath()),
+                withIntermediateDirectories: true,
+                attributes: nil
+            )
+        }
+        if !fileManager.fileExists(atPath: filePath().path) {
+            fileManager.createFile(atPath: filePath().path, contents: .init(), attributes: nil)
+        }
+    }
+
+    /// Update the local value with the value from the file.
+    private func readValue() {
+        let data = try? Data(contentsOf: filePath())
+        if let data, let value = try? JSONDecoder().decode(Value.self, from: data) {
+            rawValue = value
+        }
+    }
+
+    /// Update the value on the file with the local value.
+    private func writeCodableValue() {
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = .prettyPrinted
+        let data = try? encoder.encode(rawValue)
+        try? data?.write(to: filePath())
+    }
+
 }

Sources/Adwaita/Model/User Interface/App/App.swift

@@ -58,6 +58,7 @@ extension App {
                 appInstance.app.sceneStorage.remove(at: index)
             }
         }
+        GTUIApp.appID = appInstance.id
         appInstance.app.run()
     }
 

Sources/Adwaita/Model/User Interface/App/GTUIApp.swift

@@ -12,6 +12,8 @@ public class GTUIApp: Application {
 
     /// The handlers which are called when a state changes.
     static var updateHandlers: [() -> Void] = []
+    /// The app's id for the file name for storing the data.
+    static var appID = "temporary"
 
     /// The app's content.
     var body: () -> App

Tests/CounterDemo.swift

@@ -12,7 +12,8 @@ import Libadwaita
 
 struct CounterDemo: View {
 
-    @State private var count = 0
+    @State("count")
+    private var count = 0
 
     var view: Body {
         VStack {

Tests/Demo.swift

@@ -55,9 +55,11 @@ struct Demo: App {
 
     struct DemoContent: View {
 
-        @State private var selection: Page = .welcome
+        @State("selection")
+        private var selection: Page = .welcome
         @State private var toast: Signal = .init()
-        @State private var sidebarVisible = true
+        @State("sidebar-visible")
+        private var sidebarVisible = true
         var window: GTUIApplicationWindow
         var app: GTUIApp!
 
@@ -75,8 +77,12 @@ struct Demo: App {
                     HeaderBar.end {
                         menu
                     }
+                    .headerBarTitle {
+                        Text("Demo")
+                            .style("heading")
+                            .transition(.crossfade)
+                    }
                 }
-                .navigationTitle("Demo")
             } content: {
                 StatusPage(
                     selection.label,

Tests/Page.swift

@@ -10,7 +10,7 @@
 import Adwaita
 import Libadwaita
 
-enum Page: String, Identifiable, CaseIterable {
+enum Page: String, Identifiable, CaseIterable, Codable {
 
     case welcome
     case counter

user-manual/Basics/CreatingViews.md

@@ -133,3 +133,12 @@ struct ChangeTextView: View {
 
 Whenever you modify a state property (directly or indirectly through bindings),
 the user interface gets automatically updated to reflect that change.
+
+## Save State Values Between App Launches
+It's possible to automatically save a value that conforms to `Codable` whenever it changes to a file.
+The value in the file is read when the view containing the state value appears for the first time (e.g. when the user launches the app).
+
+Use the following syntax, where `"text"` is a unique identifier.
+```swift
+@State("text") private var text = "world"
+```