Expose BindingSource

Sources/Orbit/Components/Collapse.swift

@@ -15,12 +15,12 @@ public struct Collapse<Header: View, Content: View>: View {
 
     private let headerVerticalPadding: CGFloat
     private let showSeparator: Bool
-    private let isExpanded: Binding<Bool>?
+    private let isExpanded: OptionalBindingSource<Bool>
     @ViewBuilder private let content: Content
     @ViewBuilder private let header: Header
 
     public var body: some View {
-        BindingSource(isExpanded, fallbackInitialValue: false) { $isExpanded in
+        OptionalBinding(isExpanded) { $isExpanded in
             VStack(alignment: .leading, spacing: 0) {
                 SwiftUI.Button {
                     withAnimation(.easeInOut(duration: 0.2)) {
@@ -71,7 +71,7 @@ public extension Collapse {
         self.headerVerticalPadding = 0
         self.content = content()
         self.showSeparator = showSeparator
-        self.isExpanded = isExpanded
+        self.isExpanded = .binding(isExpanded)
     }
 
     /// Creates Orbit ``Collapse`` component.
@@ -80,7 +80,7 @@ public extension Collapse {
         self.headerVerticalPadding = 0
         self.content = content()
         self.showSeparator = showSeparator
-        self.isExpanded = nil
+        self.isExpanded = .state(false)
     }
 }
 
@@ -92,7 +92,7 @@ public extension Collapse where Header == Text {
         self.headerVerticalPadding = .small
         self.content = content()
         self.showSeparator = showSeparator
-        self.isExpanded = isExpanded
+        self.isExpanded = .binding(isExpanded)
     }
 
     /// Creates Orbit ``Collapse`` component.
@@ -101,7 +101,7 @@ public extension Collapse where Header == Text {
         self.headerVerticalPadding = .small
         self.content = content()
         self.showSeparator = showSeparator
-        self.isExpanded = nil
+        self.isExpanded = .state(false)
     }
 }
 
@@ -144,6 +144,9 @@ struct CollapsePreviews: PreviewProvider {
                     headerPlaceholder
                 }
             }
+            Collapse("Toggle with internal state") {
+                contentPlaceholder
+            }
         }
         .padding(.medium)
     }

Sources/Orbit/Support/BindingSource.swift

@@ -1,30 +1,42 @@
 import SwiftUI
 
-/// A view that provides a binding to its content.
+/// A binding source for the ``OptionalBinding``.
+public enum OptionalBindingSource<Value> {
+    case binding(Binding<Value>)
+    case state(Value)
+}
+
+/// A view that provides either a binding to its content or an internal state.
 ///
-/// This binding can either be supplied, in which case it is used directly,
-/// or one is derived from internal state (starting with `defaultValue`).
+/// The binding can either be supplied, in which case it is used directly,
+/// or one is derived from internal state.
 ///
-/// This is is useful for components that can manage their own state,
-/// but we also want to make it possible for that state to be driven
-/// from the outside if a binding is passed.
-struct BindingSource<Value, Content: View>: View {
-
-    let outer: Binding<Value>?
-    @State var inner: Value
+/// This is is useful for components that need to manage their own state,
+/// but also allow that state to be overridden 
+/// using the binding provided from the outside.
+public struct OptionalBinding<Value, Content: View>: View {
+    
+    let binding: Binding<Value>?
+    @State var state: Value
     let content: (Binding<Value>) -> Content
 
-    var body: some View {
-        content(outer ?? $inner)
+    public var body: some View {
+        content(binding ?? $state)
     }
 
-    init(
-        _ binding: Binding<Value>?,
-        fallbackInitialValue: Value,
+    public init(
+        _ source: OptionalBindingSource<Value>,
         @ViewBuilder content: @escaping (Binding<Value>) -> Content
     ) {
-        self.outer = binding
-        self._inner = State(wrappedValue: fallbackInitialValue)
+        switch source {
+            case .binding(let binding):     
+                self.binding = binding
+                self._state = .init(wrappedValue: binding.wrappedValue)
+            case .state(let value): 
+                self.binding = nil
+                self._state = State(wrappedValue: value)
+        }
+
         self.content = content
     }
 }