Add `Defaults.Toggle` (#69)

Sources/Defaults/SwiftUI.swift

@@ -5,10 +5,11 @@ import Combine
 @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
 extension Defaults {
 	final class Observable<Value: Serializable>: ObservableObject {
-		let objectWillChange = ObservableObjectPublisher()
 		private var observation: DefaultsObservation?
 		private let key: Defaults.Key<Value>
 
+		let objectWillChange = ObservableObjectPublisher()
+
 		var value: Value {
 			get { Defaults[key] }
 			set {
@@ -44,6 +45,8 @@ public struct Default<Value: Defaults.Serializable>: DynamicProperty {
 	public typealias Publisher = AnyPublisher<Defaults.KeyChange<Value>, Never>
 
 	private let key: Defaults.Key<Value>
+
+	// Intentionally using `@ObservedObjected` over `@StateObject` so that the key can be dynamicaly changed.
 	@ObservedObject private var observable: Defaults.Observable<Value>
 
 	/**
@@ -61,7 +64,10 @@ public struct Default<Value: Defaults.Serializable>: DynamicProperty {
 
 		var body: some View {
 			Text("Has Unicorn: \(hasUnicorn)")
-			Toggle("Toggle Unicorn", isOn: $hasUnicorn)
+			Toggle("Toggle", isOn: $hasUnicorn)
+			Button("Reset") {
+				_hasUnicorn.reset()
+			}
 		}
 	}
 	```
@@ -110,4 +116,101 @@ public struct Default<Value: Defaults.Serializable>: DynamicProperty {
 		key.reset()
 	}
 }
+
+@available(macOS 11, iOS 14, tvOS 14, watchOS 7, *)
+extension Defaults {
+	/**
+	Creates a SwiftUI `Toggle` view that is connected to a `Defaults` key with a `Bool` value.
+
+	The toggle works exactly like the SwiftUI `Toggle`.
+
+	```
+	extension Defaults.Keys {
+		static let showAllDayEvents = Key<Bool>("showAllDayEvents", default: false)
+	}
+
+	struct ShowAllDayEventsSetting: View {
+		var body: some View {
+			Defaults.Toggle("Show All-Day Events", key: .showAllDayEvents)
+		}
+	}
+	```
+
+	You can also listen to changes:
+
+	```
+	struct ShowAllDayEventsSetting: View {
+		var body: some View {
+			Defaults.Toggle("Show All-Day Events", key: .showAllDayEvents)
+				// Note that this has to be directly attached to `Defaults.Toggle`. It's not `View#onChange()`.
+				.onChange {
+					print("Value", $0)
+				}
+		}
+	}
+	```
+	*/
+	public struct Toggle<Label, Key>: View where Label: View, Key: Defaults.Key<Bool> {
+		@ViewStorage private var onChange: ((Bool) -> Void)?
+
+		private let label: () -> Label
+
+		// Intentionally using `@ObservedObjected` over `@StateObject` so that the key can be dynamicaly changed.
+		@ObservedObject private var observable: Defaults.Observable<Bool>
+
+		public init(key: Key, @ViewBuilder label: @escaping () -> Label) {
+			self.label = label
+			self.observable = Defaults.Observable(key)
+		}
+
+		public var body: some View {
+			SwiftUI.Toggle(isOn: $observable.value, label: label)
+				.onChange(of: observable.value) {
+					onChange?($0)
+				}
+		}
+	}
+}
+
+@available(macOS 11, iOS 14, tvOS 14, watchOS 7, *)
+extension Defaults.Toggle where Label == Text {
+	public init<S>(_ title: S, key: Defaults.Key<Bool>) where S: StringProtocol {
+		self.label = { Text(title) }
+		self.observable = Defaults.Observable(key)
+	}
+}
+
+@available(macOS 11, iOS 14, tvOS 14, watchOS 7, *)
+extension Defaults.Toggle {
+	/// Do something when the value changes to a different value.
+	public func onChange(_ action: @escaping (Bool) -> Void) -> Self {
+		onChange = action
+		return self
+	}
+}
+
+@available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
+@propertyWrapper
+private struct ViewStorage<Value>: DynamicProperty {
+	private final class ValueBox {
+		var value: Value
+
+		init(_ value: Value) {
+			self.value = value
+		}
+	}
+
+	@State private var valueBox: ValueBox
+
+	var wrappedValue: Value {
+		get { valueBox.value }
+		nonmutating set {
+			valueBox.value = newValue
+		}
+	}
+
+	init(wrappedValue value: @autoclosure @escaping () -> Value) {
+		self._valueBox = .init(wrappedValue: ValueBox(value()))
+	}
+}
 #endif

readme.md

@@ -153,6 +153,8 @@ Defaults[isUnicorn]
 
 ### SwiftUI support
 
+#### `@Default`
+
 You can use the `@Default` property wrapper to get/set a `Defaults` item and also have the view be updated when the value changes. This is similar to `@State`.
 
 ```swift
@@ -165,7 +167,10 @@ struct ContentView: View {
 
 	var body: some View {
 		Text("Has Unicorn: \(hasUnicorn)")
-		Toggle("Toggle Unicorn", isOn: $hasUnicorn)
+		Toggle("Toggle", isOn: $hasUnicorn)
+		Button("Reset") {
+			_hasUnicorn.reset()
+		}
 	}
 }
 ```
@@ -174,6 +179,38 @@ Note that it's `@Default`, not `@Defaults`.
 
 You cannot use `@Default` in an `ObservableObject`. It's meant to be used in a `View`.
 
+#### `Toggle`
+
+There's also a `SwiftUI.Toggle` wrapper that makes it easier to create a toggle based on a `Defaults` key with a `Bool` value.
+
+```swift
+extension Defaults.Keys {
+	static let showAllDayEvents = Key<Bool>("showAllDayEvents", default: false)
+}
+
+struct ShowAllDayEventsSetting: View {
+	var body: some View {
+		Defaults.Toggle("Show All-Day Events", key: .showAllDayEvents)
+	}
+}
+```
+
+You can also listen to changes:
+
+```swift
+struct ShowAllDayEventsSetting: View {
+	var body: some View {
+		Defaults.Toggle("Show All-Day Events", key: .showAllDayEvents)
+			// Note that this has to be directly attached to `Defaults.Toggle`. It's not `View#onChange()`.
+			.onChange {
+				print("Value", $0)
+			}
+	}
+}
+```
+
+*Requires at least macOS 11, iOS 14, tvOS 14, watchOS 7.*
+
 ### Observe changes to a key
 
 ```swift