Add widgets and demo application

.swiftlint.yml

@@ -118,14 +118,6 @@ custom_rules:
         message: 'Spaces should be used instead of tabs.'
         severity: warning
 
-    string_literals:
-        name: 'String Literals'
-        regex: '(".*")|("""(.|\n)*""")'
-        message: 'String literals should not be used. Disable this rule in String and LocalizedStringResource extensions.'
-        match_kinds:
-            - string
-        severity: warning
-
     # Thanks to the creator of the SwiftLint rule
     # "empty_first_line"
     # https://github.com/coteditor/CotEditor/blob/main/.swiftlint.yml

Documentation/Reference/README.md

@@ -14,10 +14,17 @@
 -   [Binding](structs/Binding.md)
 -   [Button](structs/Button.md)
 -   [EitherView](structs/EitherView.md)
+-   [HStack](structs/HStack.md)
 -   [HeaderBar](structs/HeaderBar.md)
 -   [InspectorWrapper](structs/InspectorWrapper.md)
+-   [List](structs/List.md)
+-   [NavigationSplitView](structs/NavigationSplitView.md)
+-   [ScrollView](structs/ScrollView.md)
 -   [State](structs/State.md)
+-   [StateWrapper](structs/StateWrapper.md)
+-   [StatusPage](structs/StatusPage.md)
 -   [Text](structs/Text.md)
+-   [ToolbarView](structs/ToolbarView.md)
 -   [UpdateObserver](structs/UpdateObserver.md)
 -   [VStack](structs/VStack.md)
 -   [Window](structs/Window.md)

Documentation/Reference/classes/ViewStorage.md

@@ -15,7 +15,7 @@ The view's content.
 
 ### `state`
 
-The view's state (used in `VStack`).
+The view's state (used in `StateWrapper`).
 
 ## Methods
 ### `init(_:content:state:)`

Documentation/Reference/extensions/Array.md

@@ -2,6 +2,11 @@
 
 # `Array`
 
+## Properties
+### `view`
+
+The array's view body is the array itself.
+
 ## Methods
 ### `widget()`
 

Documentation/Reference/extensions/String.md

@@ -10,3 +10,7 @@ A label for main content in a view storage.
 ### `transition`
 
 A label for the transition data in a GTUI widget's fields.
+
+### `navigationLabel`
+
+A label for the navigation label in a GTUI widget's fields.

Documentation/Reference/extensions/View.md

@@ -44,6 +44,18 @@ Enable or disable the vertical expansion.
 - Parameter enabled: Whether it is enabled or disabled.
 - Returns: A view.
 
+### `halign(_:)`
+
+Set the horizontal alignment.
+- Parameter align: The alignment.
+- Returns: A view.
+
+### `valign(_:)`
+
+Set the vertical alignment.
+- Parameter align: The alignment.
+- Returns: A view.
+
 ### `frame(minWidth:minHeight:)`
 
 Set the view's minimal width or height.
@@ -64,6 +76,40 @@ Set the view's transition.
 - Parameter transition: The transition.
 - Returns: A view.
 
+### `navigationTitle(_:)`
+
+Set the view's navigation title.
+- Parameter label: The navigation title.
+- Returns: A view.
+
+### `style(_:)`
+
+Add a style class to the view.
+- Parameter style: The style class.
+- Returns: A view.
+
+### `onAppear(_:)`
+
+Run a function when the view appears for the first time.
+- Parameter closure: The function.
+- Returns: A view.
+
+### `topToolbar(visible:_:)`
+
+Add a top toolbar to the view.
+- Parameters:
+  - toolbar: The toolbar's content.
+  - visible: Whether the toolbar is visible.
+- Returns: A view.
+
+### `bottomToolbar(visible:_:)`
+
+Add a bottom toolbar to the view.
+- Parameters:
+  - toolbar: The toolbar's content.
+  - visible: Whether the toolbar is visible.
+- Returns: A view.
+
 ### `onUpdate(_:)`
 
 Run a function when the view gets an update.

Documentation/Reference/structs/HStack.md

@@ -0,0 +1,26 @@
+**STRUCT**
+
+# `HStack`
+
+A horizontal GtkBox equivalent.
+
+## Properties
+### `content`
+
+The content.
+
+## Methods
+### `init(content:)`
+
+Initialize a `HStack`.
+- Parameter content: The view content.
+
+### `update(_:)`
+
+Update a view storage.
+- Parameter storage: The view storage.
+
+### `container()`
+
+Get a view storage.
+- Returns: The view storage.

Documentation/Reference/structs/List.md

@@ -0,0 +1,46 @@
+**STRUCT**
+
+# `List`
+
+A list box widget.
+
+## Properties
+### `elements`
+
+The elements.
+
+### `content`
+
+The content.
+
+### `selection`
+
+The identifier of the selected element.
+
+## Methods
+### `init(_:selection:content:)`
+
+Initialize `ForEach`.
+- Parameters:
+  - elements: The elements.
+  - selection: The identifier of the selected element.
+  - content: The view for an element.
+
+### `update(_:)`
+
+Update a view storage.
+- Parameter storage: The view storage.
+
+### `container()`
+
+Get a view storage.
+- Returns: The view storage.
+
+### `updateSelection(box:)`
+
+Update the list's selection.
+- Parameter box: The list box.
+
+### `sidebarStyle()`
+
+Add the "navigation-sidebar" style class.

Documentation/Reference/structs/NavigationSplitView.md

@@ -0,0 +1,40 @@
+**STRUCT**
+
+# `NavigationSplitView`
+
+A navigation split view widget.
+
+## Properties
+### `sidebar`
+
+The sidebar's content.
+
+### `content`
+
+The split view's main content.
+
+### `sidebarID`
+
+The sidebar content's id.
+
+### `contentID`
+
+The main content's id.
+
+## Methods
+### `init(sidebar:content:)`
+
+Initialize a navigation split view.
+- Parameters:
+  - sidebar: The sidebar content.
+  - content: The main content.
+
+### `container()`
+
+Get the container of the navigation split view widget.
+- Returns: The view storage.
+
+### `update(_:)`
+
+Update the view storage of the navigation split view widget.
+- Parameter storage: The view storage.

Documentation/Reference/structs/ScrollView.md

@@ -0,0 +1,26 @@
+**STRUCT**
+
+# `ScrollView`
+
+A GtkScrolledWindow equivalent.
+
+## Properties
+### `content`
+
+The content.
+
+## Methods
+### `init(content:)`
+
+Initialize a `ScrollView`.
+- Parameter content: The view content.
+
+### `update(_:)`
+
+Update a view storage.
+- Parameter storage: The view storage.
+
+### `container()`
+
+Get a view storage.
+- Returns: The view storage.

Documentation/Reference/structs/StateWrapper.md

@@ -0,0 +1,37 @@
+**STRUCT**
+
+# `StateWrapper`
+
+A storage for `@State` properties.
+
+## Properties
+### `content`
+
+The content.
+
+### `state`
+
+The state information (from properties with the `State` wrapper).
+
+## Methods
+### `init(content:)`
+
+Initialize a `StateWrapper`.
+- Parameter content: The view content.
+
+### `init(content:state:)`
+
+Initialize a `StateWrapper`.
+- Parameters:
+  - content: The view content.
+  - state: The state information.
+
+### `update(_:)`
+
+Update a view storage.
+- Parameter storage: The view storage.
+
+### `container()`
+
+Get a view storage.
+- Returns: The view storage.

Documentation/Reference/structs/StatusPage.md

@@ -0,0 +1,42 @@
+**STRUCT**
+
+# `StatusPage`
+
+A status page widget.
+
+## Properties
+### `title`
+
+The title.
+
+### `description`
+
+The description.
+
+### `icon`
+
+The icon.
+
+### `content`
+
+Additional content.
+
+## Methods
+### `init(_:icon:description:content:)`
+
+Initialize a status page widget.
+- Parameters:
+  - title: The title.
+  - icon: The icon.
+  - description: Additional details.
+  - content: Additional content.
+
+### `update(_:)`
+
+Update the view storage of the text widget.
+- Parameter storage: The view storage.
+
+### `container()`
+
+Get the container of the text widget.
+- Returns: The view storage.

Documentation/Reference/structs/ToolbarView.md

@@ -0,0 +1,37 @@
+**STRUCT**
+
+# `ToolbarView`
+
+A toolbar view widget.
+
+## Properties
+### `content`
+
+The sidebar's content.
+
+### `toolbar`
+
+The toolbars.
+
+### `bottom`
+
+Whether the toolbars are bottom toolbars.
+
+### `visible`
+
+Whether the toolbar is visible.
+
+### `toolbarID`
+
+The identifier of the toolbar content.
+
+## Methods
+### `container()`
+
+Get the container of the toolbar view widget.
+- Returns: The view storage.
+
+### `update(_:)`
+
+Update the view storage of the toolbar view widget.
+- Parameter storage: The view storage.

Documentation/Reference/structs/VStack.md

@@ -9,23 +9,12 @@ A GtkBox equivalent.
 
 The content.
 
-### `state`
-
-The state information (from properties with the `State` wrapper).
-
 ## Methods
 ### `init(content:)`
 
 Initialize a `VStack`.
 - Parameter content: The view content.
 
-### `init(content:state:)`
-
-Initialize a `VStack`.
-- Parameters:
-  - content: The view content.
-  - state: The state information.
-
 ### `update(_:)`
 
 Update a view storage.

Package.swift

@@ -26,7 +26,7 @@ let package = Package(
             dependencies: [.product(name: "GTUI", package: "swiftgui")]
         ),
         .executableTarget(
-            name: "Counter",
+            name: "Swift Adwaita Demo",
             dependencies: ["Adwaita"],
             path: "Tests"
         )

README.md

@@ -27,16 +27,19 @@ struct Example: View {
     @State private var count = 0
 
     var view: Body {
-        HeaderBar.start {
-            Button(icon: .default(icon: .goPrevious)) {
-                count -= 1
-            }
-            Button(icon: .default(icon: .goNext)) {
-                count += 1
-            }
-        }
         Text("\(count)")
+            .style("title-1")
             .padding(50)
+            .topToolbar {
+                HeaderBar.start {
+                    Button(icon: .default(icon: .goPrevious)) {
+                        count -= 1
+                    }
+                    Button(icon: .default(icon: .goNext)) {
+                        count += 1
+                    }
+                }
+            }
     }
 
 }
@@ -46,49 +49,66 @@ Creates a simple counter view:
 
 ![Counter Example][image-1]
 
+More examples are available in the [Demo app][1]:
+
+![Demo App][image-2]
+
 ## Table of Contents
 
-- [Goals][1]
+- [Goals][2]
-- [Widgets][2]
+- [Widgets][3]
-- [Installation][3]
+- [Installation][4]
-- [Usage][4]
+- [Usage][5]
-- [Thanks][5]
+- [Thanks][6]
 
 ## Goals
 
-_Adwaita_’s main goal is to provide an easy-to-use interface for creating GNOME apps. The backend should stay as simple as possible, while not limiting the possibilities there are with [Libadwaita][6] and [GTK][7].
+_Adwaita_’s main goal is to provide an easy-to-use interface for creating GNOME apps. The backend should stay as simple as possible, while not limiting the possibilities there are with [Libadwaita][7] and [GTK][8].
 
-If you want to use _Adwaita_ in a project, but there are widgets missing, open an [issue on GitHub][8].
+If you want to use _Adwaita_ in a project, but there are widgets missing, open an [issue on GitHub][9].
 
 ## Widgets
 
-| Name       | Description                                                       | Widget       |
+| Name                 | Description                                                       | Widget                 |
-| ---------- | ----------------------------------------------------------------- | ------------ |
+| -------------------- | ----------------------------------------------------------------- | ---------------------- |
-| Button     | A widget that triggers a function when being clicked.             | GtkButton    |
+| Button               | A widget that triggers a function when being clicked.             | GtkButton              |
-| EitherView | A widget that displays one of its child views based on a boolean. | GtkStack     |
+| EitherView           | A widget that displays one of its child views based on a boolean. | GtkStack               |
-| HeaderBar  | A widget for creating custom title bars for windows.              | GtkHeaderBar |
+| HeaderBar            | A widget for creating custom title bars for windows.              | GtkHeaderBar           |
-| Text       | A widget for displaying a small amount of text.                   | GtkLabel     |
+| Text                 | A widget for displaying a small amount of text.                   | GtkLabel               |
-| VStack     | A widget which arranges child widgets into a single column.       | GtkBox       |
+| VStack               | A widget which arranges child widgets into a single column.       | GtkBox                 |
+| HStack               | A widget which arranges child widgets into a single row.          | GtkBox                 |
+| List                 | A widget which arranges child widgets vertically into rows.       | GtkListBox             |
+| NavigationSplitView  | A widget presenting sidebar and content side by side.             | AdwNavigationSplitView |
+| ScrollView           | A container that makes its child scrollable.                      | GtkScrolledWindow      |
+| StatusPage           | A page with an icon, title, and optionally description and widget.| AdwStatusPage          |
+| StateWrapper         | A wrapper not affecting the UI which stores state information.    | -                      |
 
 ### View Modifiers
 
 | Syntax                       | Description                                                                            |
 | ---------------------------- | -------------------------------------------------------------------------------------- |
-| `inspect(_:)`                | Edit the underlying [GTUI][9] widget.                                                  |
+| `inspect(_:)`                | Edit the underlying [GTUI][10] widget.                                                  |
 | `padding(_:_:)`              | Add empty space around a view.                                                         |
 | `hexpand(_:)`                | Enable or disable the horizontal expansion of a view.                                  |
 | `vexpand(_:)`                | Enable or disable the vertical expansion of a view.                                    |
+| `halign(_:)`                 | Set the horizontal alignment of a view.                                                |
+| `valign(_:)`                 | Set the vertical alignment of a view.                                                  |
 | `frame(minWidth:minHeight:)` | Set the view’s minimal width or height.                                                |
 | `frame(maxSize:)`            | Set the view’s maximal size.                                                           |
-| `transition(_:)`             | Assign a transition with the view that is used if it is a direct child of a HeaderBar. |
+| `transition(_:)`             | Assign a transition with the view that is used if it is a direct child of an EitherView. |
 | `onUpdate(_:)`               | Run a function every time a view gets updated.                                         |
+| `navigationTitle(_:)`        | Add a title that is used if the view is a direct child of a NavigationView.            |
+| `style(_:)`                  | Add a style class to the view.                                                         |
+| `onAppear(_:)`               | Run when the view is rendered for the first time.                                      |
+| `topToolbar(visible:_:)`             | Add a native toolbar to the view. Normally, it contains a HeaderBar.                   |
+| `bottomToolbar(visible:_:)`          | Add a native bottom toolbar to the view.                                               |
 
 ## Installation
 ### Dependencies
 If you are using a Linux distribution, install `libadwaita-devel` or `libadwaita` (or something similar, based on the package manager) as well as `gtk4-devel`, `gtk4` or similar.
 
 On macOS, follow these steps:
-1. Install [Homebrew][10].
+1. Install [Homebrew][11].
 2. Install Libadwaita (and thereby GTK 4):
 ```
 brew install libadwaita
@@ -104,45 +124,52 @@ brew install libadwaita
 
 ## Usage
 
-* [Getting Started][11]
+* [Getting Started][12]
 
 ### Basics
 
-* [Hello World][12]
+* [Hello World][13]
-* [Creating Views][13]
+* [Creating Views][14]
-* [Windows][14]
+* [Windows][15]
+
+### Advanced
+
+* [Creating Widgets][16]
 
 ## Thanks
 
 ### Dependencies
-- [SwiftGui][15] licensed under the [GPL-3.0 license][16]
+- [SwiftGui][17] licensed under the [GPL-3.0 license][18]
 
 ### Other Thanks
-- The [contributors][17]
+- The [contributors][19]
-- [SwiftLint][18] for checking whether code style conventions are violated
+- [SwiftLint][20] for checking whether code style conventions are violated
-- The programming language [Swift][19]
+- The programming language [Swift][21]
-- [SourceDocs][20] used for generating the [docs][21]
+- [SourceDocs][22] used for generating the [docs][23]
 
-[1]:	#goals
+[1]:    Tests/
-[2]:	#widgets
+[2]:	#goals
-[3]:	#installation
+[3]:	#widgets
-[4]:	#usage
+[4]:	#installation
-[5]:	#thanks
+[5]:	#usage
-[6]:	https://gnome.pages.gitlab.gnome.org/libadwaita/doc/1-latest/index.html
+[6]:	#thanks
-[7]:	https://docs.gtk.org/gtk4/
+[7]:	https://gnome.pages.gitlab.gnome.org/libadwaita/doc/1-latest/index.html
-[8]:	https://github.com/david-swift/Adwaita/issues
+[8]:	https://docs.gtk.org/gtk4/
-[9]:	https://github.com/JCWasmx86/SwiftGui
+[9]:	https://github.com/david-swift/Adwaita/issues
-[10]:	https://brew.sh
+[10]:	https://github.com/JCWasmx86/SwiftGui
-[11]:	user-manual/GettingStarted.md
+[11]:	https://brew.sh
-[12]:	user-manual/Basics/HelloWorld.md
+[12]:	user-manual/GettingStarted.md
-[13]:   user-manual/Basics/CreatingViews.md
+[13]:	user-manual/Basics/HelloWorld.md
-[14]:   user-manual/Basics/Windows.md
+[14]: user-manual/Basics/CreatingViews.md
-[15]:	https://github.com/JCWasmx86/SwiftGui
+[15]: user-manual/Basics/Windows.md
-[16]:	https://github.com/JCWasmx86/SwiftGui/blob/main/COPYING
+[16]: user-manual/Advanced/CreatingWidgets.md
-[17]:	Contributors.md
+[17]:	https://github.com/JCWasmx86/SwiftGui
-[18]:	https://github.com/realm/SwiftLint
+[18]:	https://github.com/JCWasmx86/SwiftGui/blob/main/COPYING
-[19]:	https://github.com/apple/swift
+[19]:	Contributors.md
-[20]:	https://github.com/SourceDocs/SourceDocs
+[20]:	https://github.com/realm/SwiftLint
-[21]:	Documentation/Reference/README.md
+[21]:	https://github.com/apple/swift
+[22]:	https://github.com/SourceDocs/SourceDocs
+[23]:	Documentation/Reference/README.md
 
 [image-1]: Icons/Screenshot.png
+[image-2]: Icons/Demo.png

SUMMARY.md

@@ -9,8 +9,13 @@
 * [Creating Views][4]
 * [Windows][5]
 
+## Advanced
+
+* [Creating Widgets][6]
+
 [1]:	README.md
 [2]:	user-manual/GettingStarted.md
 [3]:	user-manual/Basics/HelloWorld.md
-[4]:    user-manual/Basics/CreatingViews.md
+[4]:   user-manual/Basics/CreatingViews.md
-[5]:    user-manual/Basics/Windows.md
+[5]:   user-manual/Basics/Windows.md
+[6]:   user-manual/Advanced/CreatingWidgets.md

Sources/Adwaita/Model/Extensions/Array.swift

@@ -7,7 +7,10 @@
 
 import GTUI
 
-extension Array where Element == View {
+extension Array: View where Element == View {
+
+    /// The array's view body is the array itself.
+    public var view: Body { self }
 
     /// Get a widget from a collection of views.
     /// - Returns: A widget.

Sources/Adwaita/Model/Extensions/String.swift

@@ -11,5 +11,7 @@ extension String {
     static var mainContent: Self { "main" }
     /// A label for the transition data in a GTUI widget's fields.
     static var transition: Self { "transition" }
+    /// A label for the navigation label in a GTUI widget's fields.
+    static var navigationLabel: Self { "navigation-label" }
 
 }

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

@@ -41,7 +41,7 @@ extension View {
                     state[label] = value
                 }
             }
-            return VStack(content: { view }, state: state)
+            return StateWrapper(content: { view }, state: state)
         }
     }
 
@@ -50,6 +50,8 @@ extension View {
     func updateStorage(_ storage: ViewStorage) {
         if let widget = self as? Widget {
             widget.update(storage)
+        } else {
+            StateWrapper { self }.update(storage)
         }
     }
 

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

@@ -14,7 +14,7 @@ public class ViewStorage {
     public var view: NativeWidgetPeer
     /// The view's content.
     public var content: [String: [ViewStorage]]
-    /// The view's state (used in `VStack`).
+    /// The view's state (used in `StateWrapper`).
     public var state: [String: StateProtocol]
 
     /// Initialize a view storage.

Sources/Adwaita/View/HStack.swift

@@ -0,0 +1,41 @@
+//
+//  HStack.swift
+//  Adwaita
+//
+//  Created by david-swift on 26.09.23.
+//
+
+import GTUI
+
+/// A horizontal GtkBox equivalent.
+public struct HStack: Widget {
+
+    /// The content.
+    var content: () -> Body
+
+    /// Initialize a `HStack`.
+    /// - Parameter content: The view content.
+    public init(@ViewBuilder content: @escaping () -> Body) {
+        self.content = content
+    }
+
+    /// Update a view storage.
+    /// - Parameter storage: The view storage.
+    public func update(_ storage: ViewStorage) {
+        content().update(storage.content[.mainContent] ?? [])
+    }
+
+    /// Get a view storage.
+    /// - Returns: The view storage.
+    public func container() -> ViewStorage {
+        let box: Box = .init(horizontal: true)
+        var content: [ViewStorage] = []
+        for element in self.content() {
+            let widget = element.storage()
+            _ = box.append(widget.view)
+            content.append(widget)
+        }
+        return .init(box, content: [.mainContent: content])
+    }
+
+}

Sources/Adwaita/View/List.swift

@@ -0,0 +1,76 @@
+//
+//  List.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+import GTUI
+
+/// A list box widget.
+public struct List<Element>: Widget where Element: Identifiable {
+
+    /// The elements.
+    var elements: [Element]
+    /// The content.
+    var content: (Element) -> Body
+    /// The identifier of the selected element.
+    @Binding var selection: Element.ID
+
+    /// Initialize `ForEach`.
+    /// - Parameters:
+    ///   - elements: The elements.
+    ///   - selection: The identifier of the selected element.
+    ///   - content: The view for an element.
+    public init(
+        _ elements: [Element],
+        selection: Binding<Element.ID>,
+        @ViewBuilder content: @escaping (Element) -> Body
+    ) {
+        self.content = content
+        self.elements = elements
+        self._selection = selection
+    }
+
+    /// Update a view storage.
+    /// - Parameter storage: The view storage.
+    public func update(_ storage: ViewStorage) {
+        if let box = storage.view as? ListBox {
+            updateSelection(box: box)
+        }
+    }
+
+    /// Get a view storage.
+    /// - Returns: The view storage.
+    public func container() -> ViewStorage {
+        let box: ListBox = .init()
+        var content: [ViewStorage] = []
+        for element in elements {
+            let widget = self.content(element).widget().container()
+            _ = box.append(widget.view)
+            content.append(widget)
+        }
+        _ = box.handler {
+            let selection = box.getSelectedRow()
+            if let id = elements[safe: selection]?.id {
+                self.selection = id
+            }
+        }
+        updateSelection(box: box)
+        return .init(box, content: [.mainContent: content])
+    }
+
+    /// Update the list's selection.
+    /// - Parameter box: The list box.
+    func updateSelection(box: ListBox) {
+        if let index = elements.firstIndex(where: { $0.id == selection }) {
+            box.selectRow(at: index)
+        }
+    }
+
+    /// Add the "navigation-sidebar" style class.
+    public func sidebarStyle() -> View {
+        style("navigation-sidebar")
+    }
+
+}

Sources/Adwaita/View/Modifiers/InspectorWrapper.swift

@@ -63,6 +63,20 @@ extension View {
         inspect { _ = $0?.vexpand() }
     }
 
+    /// Set the horizontal alignment.
+    /// - Parameter align: The alignment.
+    /// - Returns: A view.
+    public func halign(_ align: Alignment) -> View {
+        inspect { _ = $0?.halign(align) }
+    }
+
+    /// Set the vertical alignment.
+    /// - Parameter align: The alignment.
+    /// - Returns: A view.
+    public func valign(_ align: Alignment) -> View {
+        inspect { _ = $0?.valign(align) }
+    }
+
     /// Set the view's minimal width or height.
     /// - Parameters:
     ///   - minWidth: The minimal width.
@@ -86,4 +100,25 @@ extension View {
         inspect { $0?.fields[.transition] = transition }
     }
 
+    /// Set the view's navigation title.
+    /// - Parameter label: The navigation title.
+    /// - Returns: A view.
+    public func navigationTitle(_ label: String) -> View {
+        inspect { $0?.fields[.navigationLabel] = label }
+    }
+
+    /// Add a style class to the view.
+    /// - Parameter style: The style class.
+    /// - Returns: A view.
+    public func style(_ style: String) -> View {
+        inspect { _ = $0?.addStyle(style) }
+    }
+
+    /// Run a function when the view appears for the first time.
+    /// - Parameter closure: The function.
+    /// - Returns: A view.
+    public func onAppear(_ closure: @escaping () -> Void) -> View {
+        inspect { _ in closure() }
+    }
+
 }

Sources/Adwaita/View/Modifiers/ToolbarView.swift

@@ -0,0 +1,90 @@
+//
+//  ToolbarView.swift
+//  Adwaita
+//
+//  Created by david-swift on 24.09.23.
+//
+
+import GTUI
+
+/// A toolbar view widget.
+struct ToolbarView: Widget {
+
+    /// The sidebar's content.
+    var content: View
+    /// The toolbars.
+    var toolbar: () -> Body
+    /// Whether the toolbars are bottom toolbars.
+    var bottom: Bool
+    /// Whether the toolbar is visible.
+    var visible: Bool
+
+    /// The identifier of the toolbar content.
+    let toolbarID = "toolbar"
+
+    /// Get the container of the toolbar view widget.
+    /// - Returns: The view storage.
+    func container() -> ViewStorage {
+        let content = content.storage()
+        let view = GTUI.ToolbarView(content.view)
+        var toolbarContent: [ViewStorage] = []
+        for item in toolbar() {
+            let storage = item.storage()
+            toolbarContent.append(storage)
+            if bottom {
+                _ = view.addBottomBar(storage.view)
+            } else {
+                _ = view.addTopBar(storage.view)
+            }
+        }
+        if bottom {
+            view.setRevealBottomBar(visible)
+        } else {
+            view.setRevealTopBar(visible)
+        }
+        return .init(view, content: [.mainContent: [content], toolbarID: toolbarContent])
+    }
+
+    /// Update the view storage of the toolbar view widget.
+    /// - Parameter storage: The view storage.
+    func update(_ storage: ViewStorage) {
+        if let mainContent = storage.content[.mainContent]?.first {
+            content.widget().update(mainContent)
+        }
+        if let toolbar = storage.content[toolbarID] {
+            for (index, content) in toolbar.enumerated() {
+                self.toolbar()[safe: index]?.updateStorage(content)
+            }
+        }
+        if let view = storage.view as? GTUI.ToolbarView {
+            if bottom {
+                view.setRevealBottomBar(visible)
+            } else {
+                view.setRevealTopBar(visible)
+            }
+        }
+    }
+
+}
+
+extension View {
+
+    /// Add a top toolbar to the view.
+    /// - Parameters:
+    ///   - toolbar: The toolbar's content.
+    ///   - visible: Whether the toolbar is visible.
+    /// - Returns: A view.
+    public func topToolbar(visible: Bool = true, @ViewBuilder _ toolbar: @escaping () -> Body) -> View {
+        ToolbarView(content: self, toolbar: toolbar, bottom: false, visible: visible)
+    }
+
+    /// Add a bottom toolbar to the view.
+    /// - Parameters:
+    ///   - toolbar: The toolbar's content.
+    ///   - visible: Whether the toolbar is visible.
+    /// - Returns: A view.
+    public func bottomToolbar(visible: Bool = true, @ViewBuilder _ toolbar: @escaping () -> Body) -> View {
+        ToolbarView(content: self, toolbar: toolbar, bottom: true, visible: visible)
+    }
+
+}

Sources/Adwaita/View/NavigationSplitView.swift

@@ -0,0 +1,62 @@
+//
+//  NavigationSplitView.swift
+//  Adwaita
+//
+//  Created by david-swift on 24.09.23.
+//
+
+import GTUI
+
+/// A navigation split view widget.
+public struct NavigationSplitView: Widget {
+
+    /// The sidebar's content.
+    var sidebar: () -> Body
+    /// The split view's main content.
+    var content: () -> Body
+
+    /// The sidebar content's id.
+    let sidebarID = "sidebar"
+    /// The main content's id.
+    let contentID = "content"
+
+    /// Initialize a navigation split view.
+    /// - Parameters:
+    ///   - sidebar: The sidebar content.
+    ///   - content: The main content.
+    public init(@ViewBuilder sidebar: @escaping () -> Body, @ViewBuilder content: @escaping () -> Body) {
+        self.sidebar = sidebar
+        self.content = content
+    }
+
+    /// Get the container of the navigation split view widget.
+    /// - Returns: The view storage.
+    public func container() -> ViewStorage {
+        let splitView: GTUI.NavigationSplitView = .init()
+        var content: [String: [ViewStorage]] = [:]
+
+        let sidebar = sidebar().widget().container()
+        let label = sidebar.view.fields[.navigationLabel] as? String ?? ""
+        _ = splitView.sidebar(sidebar.view, title: label)
+        content[sidebarID] = [sidebar]
+
+        let mainContent = self.content().widget().container()
+        let mainLabel = mainContent.view.fields[.navigationLabel] as? String ?? ""
+        _ = splitView.content(mainContent.view, title: mainLabel)
+        content[contentID] = [mainContent]
+
+        return .init(splitView, content: content)
+    }
+
+    /// Update the view storage of the navigation split view widget.
+    /// - Parameter storage: The view storage.
+    public func update(_ storage: ViewStorage) {
+        if let storage = storage.content[contentID]?[safe: 0] {
+            content().widget().update(storage)
+        }
+        if let storage = storage.content[sidebarID]?[safe: 0] {
+            sidebar().widget().update(storage)
+        }
+    }
+
+}

Sources/Adwaita/View/ScrollView.swift

@@ -0,0 +1,37 @@
+//
+//  ScrollView.swift
+//  Adwaita
+//
+//  Created by david-swift on 26.09.23.
+//
+
+import GTUI
+
+/// A GtkScrolledWindow equivalent.
+public struct ScrollView: Widget {
+
+    /// The content.
+    var content: () -> Body
+
+    /// Initialize a `ScrollView`.
+    /// - Parameter content: The view content.
+    public init(@ViewBuilder content: @escaping () -> Body) {
+        self.content = content
+    }
+
+    /// Update a view storage.
+    /// - Parameter storage: The view storage.
+    public func update(_ storage: ViewStorage) {
+        if let first = storage.content[.mainContent]?.first {
+          content().widget().update(first)
+        }
+    }
+
+    /// Get a view storage.
+    /// - Returns: The view storage.
+    public func container() -> ViewStorage {
+        let container = content().widget().container()
+        return .init(Scrolled().setChild(container.view), content: [.mainContent: [container]])
+    }
+
+}

Sources/Adwaita/View/StateWrapper.swift

@@ -0,0 +1,53 @@
+//
+//  StateWrapper.swift
+//  Adwaita
+//
+//  Created by david-swift on 26.09.23.
+//
+
+import GTUI
+
+/// A storage for `@State` properties.
+public struct StateWrapper: Widget {
+
+    /// The content.
+    var content: () -> Body
+    /// The state information (from properties with the `State` wrapper).
+    var state: [String: StateProtocol] = [:]
+
+    /// Initialize a `StateWrapper`.
+    /// - Parameter content: The view content.
+    public init(@ViewBuilder content: @escaping () -> Body) {
+        self.content = content
+    }
+
+    /// Initialize a `StateWrapper`.
+    /// - Parameters:
+    ///   - content: The view content.
+    ///   - state: The state information.
+    init(content: @escaping () -> Body, state: [String: StateProtocol]) {
+        self.content = content
+        self.state = state
+    }
+
+    /// Update a view storage.
+    /// - Parameter storage: The view storage.
+    public func update(_ storage: ViewStorage) {
+        for property in state {
+            if let value = storage.state[property.key]?.value {
+                property.value.value = value
+            }
+        }
+        if let storage = storage.content[.mainContent]?.first {
+            content().widget().update(storage)
+        }
+    }
+
+    /// Get a view storage.
+    /// - Returns: The view storage.
+    public func container() -> ViewStorage {
+        let content = content().widget().container()
+        return .init(content.view, content: [.mainContent: [content]], state: state)
+    }
+
+}

Sources/Adwaita/View/StatusPage.swift

@@ -0,0 +1,56 @@
+//
+//  StatusPage.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+import GTUI
+
+/// A status page widget.
+public struct StatusPage: Widget {
+
+    /// The title.
+    var title: String
+    /// The description.
+    var description: String
+    /// The icon.
+    var icon: Icon
+    /// Additional content.
+    var content: Body
+
+    /// Initialize a status page widget.
+    /// - Parameters:
+    ///   - title: The title.
+    ///   - icon: The icon.
+    ///   - description: Additional details.
+    ///   - content: Additional content.
+    public init(_ title: String, icon: Icon, description: String = "", @ViewBuilder content: () -> Body = { [] }) {
+        self.title = title
+        self.description = description
+        self.icon = icon
+        self.content = content()
+    }
+
+    /// Update the view storage of the text widget.
+    /// - Parameter storage: The view storage.
+    public func update(_ storage: ViewStorage) {
+        if let statusPage = storage.view as? GTUI.StatusPage {
+            _ = statusPage.title(title).description(description).icon(icon)
+        }
+        if let storage = storage.content[.mainContent]?.first {
+            content.widget().update(storage)
+        }
+    }
+
+    /// Get the container of the text widget.
+    /// - Returns: The view storage.
+    public func container() -> ViewStorage {
+        let child = content.widget().container()
+        return .init(
+            GTUI.StatusPage().title(title).description(description).icon(icon).child(child.view),
+            content: [.mainContent: [child]]
+        )
+    }
+
+}

Sources/Adwaita/View/Text.swift

@@ -1,5 +1,5 @@
 //
-//  HeaderBar.swift
+//  Text.swift
 //  Adwaita
 //
 //  Created by david-swift on 23.08.23.

Sources/Adwaita/View/VStack.swift

@@ -1,5 +1,5 @@
 //
-//  EitherView.swift
+//  VStack.swift
 //  Adwaita
 //
 //  Created by david-swift on 23.08.23.
@@ -12,8 +12,6 @@ public struct VStack: Widget {
 
     /// The content.
     var content: () -> Body
-    /// The state information (from properties with the `State` wrapper).
-    var state: [String: StateProtocol] = [:]
 
     /// Initialize a `VStack`.
     /// - Parameter content: The view content.
@@ -21,23 +19,9 @@ public struct VStack: Widget {
         self.content = content
     }
 
-    /// Initialize a `VStack`.
-    /// - Parameters:
-    ///   - content: The view content.
-    ///   - state: The state information.
-    init(content: @escaping () -> Body, state: [String: StateProtocol]) {
-        self.content = content
-        self.state = state
-    }
-
     /// Update a view storage.
     /// - Parameter storage: The view storage.
     public func update(_ storage: ViewStorage) {
-        for property in state {
-            if let value = storage.state[property.key]?.value {
-                property.value.value = value
-            }
-        }
         content().update(storage.content[.mainContent] ?? [])
     }
 
@@ -51,7 +35,7 @@ public struct VStack: Widget {
             _ = box.append(widget.view)
             content.append(widget)
         }
-        return .init(box, content: [.mainContent: content], state: state)
+        return .init(box, content: [.mainContent: content])
     }
 
 }

Tests/CounterDemo.swift

@@ -0,0 +1,37 @@
+//
+//  CounterDemo.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+// swiftlint:disable missing_docs
+
+import Adwaita
+
+struct CounterDemo: View {
+
+    @State private var count = 0
+
+    var view: Body {
+        description
+            .topToolbar {
+                HeaderBar.start {
+                    Button(icon: .default(icon: .goPrevious)) {
+                        count -= 1
+                    }
+                    Button(icon: .default(icon: .goNext)) {
+                        count += 1
+                    }
+                }
+            }
+    }
+
+    @ViewBuilder private var description: Body {
+        Text("\(count)")
+            .style("title-1")
+    }
+
+}
+
+// swiftlint:enable missing_docs

Tests/Demo.swift

@@ -0,0 +1,68 @@
+//
+//  Demo.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+// swiftlint:disable missing_docs implicitly_unwrapped_optional no_magic_numbers
+
+import Adwaita
+import GTUI
+
+@main
+struct Demo: App {
+
+    let id = "io.github.david-swift.Demo"
+    var app: GTUIApp!
+    @State private var toolbar = false
+
+    var scene: Scene {
+        Window(id: "main") { window in
+            DemoContent(window: window, app: app)
+        }
+        Window(id: "content", open: 0) { window in
+            Text("This window exists at most once.")
+                .padding()
+                .topToolbar {
+                    HeaderBar.empty()
+                }
+                .onAppear {
+                    window.setDefaultSize(width: 400, height: 250)
+                }
+        }
+    }
+
+    struct DemoContent: View {
+
+        @State private var selection: Page = .welcome
+        var window: GTUI.Window
+        var app: GTUIApp!
+
+        var view: Body {
+            NavigationSplitView {
+                ScrollView {
+                    List(Page.allCases, selection: $selection) { element in
+                        Text(element.label)
+                            .halign(.start)
+                            .padding()
+                    }
+                    .sidebarStyle()
+                }
+                .topToolbar {
+                    HeaderBar.empty()
+                }
+                .navigationTitle("Demo")
+            } content: {
+                selection.view(app: app)
+            }
+            .onAppear {
+                window.setDefaultSize(width: 650, height: 450)
+            }
+        }
+
+    }
+
+}
+
+// swiftlint:enable missing_docs implicitly_unwrapped_optional no_magic_numbers

Tests/Page.swift

@@ -0,0 +1,40 @@
+//
+//  Page.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+// swiftlint:disable missing_docs implicitly_unwrapped_optional
+
+import Adwaita
+
+enum Page: String, Identifiable, CaseIterable {
+
+    case welcome
+    case counter
+    case windows
+
+    var id: Self {
+        self
+    }
+
+    var label: String {
+        rawValue.capitalized
+    }
+
+    @ViewBuilder
+    func view(app: GTUIApp!) -> Body {
+        switch self {
+        case .welcome:
+            WelcomeDemo()
+        case .counter:
+            CounterDemo()
+        case .windows:
+            WindowsDemo(app: app)
+        }
+    }
+
+}
+
+// swiftlint:enable missing_docs implicitly_unwrapped_optional

Tests/WelcomeDemo.swift

@@ -0,0 +1,29 @@
+//
+//  WelcomeDemo.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+// swiftlint:disable missing_docs
+
+import Adwaita
+
+struct WelcomeDemo: View {
+
+    @State private var test = false
+
+    var view: Body {
+        StatusPage(
+            "Swift Adwaita Demo",
+            icon: .default(icon: .gnomeAdwaita1Demo),
+            description: "This is a collection of examples for the Swift Adwaita package."
+        )
+        .topToolbar {
+            HeaderBar.empty()
+        }
+    }
+
+}
+
+// swiftlint:enable missing_docs

Tests/WindowsDemo.swift

@@ -0,0 +1,34 @@
+//
+//  WindowsDemo.swift
+//  Adwaita
+//
+//  Created by david-swift on 25.09.23.
+//
+
+// swiftlint:disable missing_docs implicitly_unwrapped_optional no_magic_numbers
+
+import Adwaita
+
+struct WindowsDemo: View {
+
+    var app: GTUIApp!
+
+    var view: Body {
+        VStack {
+            Button("Show Window") {
+                app.showWindow("content")
+            }
+            .padding()
+            Button("Add Window") {
+                app.addWindow("main")
+            }
+            .padding(10, .horizontal.add(.bottom))
+        }
+        .topToolbar {
+            HeaderBar.empty()
+        }
+    }
+
+}
+
+// swiftlint:enable missing_docs implicitly_unwrapped_optional no_magic_numbers

Tests/main.swift

@@ -1,72 +0,0 @@
-//
-//  main.swift
-//  Adwaita
-//
-//  Created by david-swift on 05.08.23.
-//
-
-// swiftlint:disable missing_docs implicitly_unwrapped_optional no_magic_numbers
-
-import Adwaita
-
-@main
-struct Counter: App {
-
-    let id = "io.github.david-swift.Counter"
-    var app: GTUIApp!
-
-    var scene: Scene {
-        Window(id: "toggle") { _ in
-            Button("Add Window") {
-                app.addWindow("content-view")
-            }
-            .padding()
-            Button("Show Window") {
-                app.showWindow("content-view")
-            }
-            .padding(10, .horizontal.add(.bottom))
-        }
-        Window(id: "content-view", open: 0) { _ in
-            ContentView()
-        }
-    }
-
-}
-
-struct ContentView: View {
-
-    @State private var count = 0
-
-    var view: Body {
-        HeaderBar.start {
-            Button(icon: .default(icon: .goPrevious)) {
-                count -= 1
-            }
-            Button(icon: .default(icon: .goNext)) {
-                count += 1
-            }
-        }
-        description
-    }
-
-    @ViewBuilder private var description: Body {
-        VStack {
-            switch count {
-            case 1:
-                Text("One")
-                  .transition(.slideUp)
-            case 0:
-                Text("Zero")
-            default:
-                Text("Hello, world, \(count)!")
-            }
-        }
-        .padding(50)
-        .onUpdate {
-            print(count)
-        }
-    }
-
-}
-
-// swiftlint:enable missing_docs implicitly_unwrapped_optional no_magic_numbers

user-manual/Advanced/CreatingWidgets.md

@@ -0,0 +1,64 @@
+# Creating Widgets
+
+Widgets are special views that do not provide a collection of other views as a content,
+but have functions that are called when creating or updating the view.
+Normally, a widget manages a GTK or Libadwaita widget using [SwiftGui][1].
+
+## Recreate the `Text` widget
+In this tutorial, we will recreate the text widget.
+A widget conforms to the `Widget` protocol:
+```swift
+struct CustomText: Widget { }
+```
+You can add properties to the widget:
+```swift
+struct CustomText: Widget {
+
+    var text: String
+
+}
+```
+This widget can be called in a view body using `CustomText(text: "Hello, world!")`.
+Now, add the two functions required by the protocol:
+```swift
+struct CustomText: Widget {
+
+    var text: String
+
+    public func container() -> ViewStorage { }
+    public func update(_ storage: ViewStorage) { }
+
+}
+```
+
+## The `container()` Function
+This function initializes the widget when the widget appears for the first time.
+It expects a `ViewStorage` as the return type.
+In our case, this function is very simple:
+```swift
+func container() -> ViewStorage {
+    .init(MarkupLabel(self.text))
+}
+```
+`MarkupLabel` is defined in [SwiftGui][1].
+
+## The `update(_:)` Function
+Whenever a state of the app changes, the `update(_:)` function of the widget gets called.
+You get the view storage that you have previously initialized as a parameter.
+Update the storage to reflect the current state of the widget:
+```swift
+func update(_ storage: ViewStorage) {
+    if let label = storage.view as? MarkupLabel {
+        label.setText(text)
+    }
+}
+```
+
+## Containers
+Some widgets act as containers that accept other widgets as children.
+In that case, use the `ViewStorage`'s `content` property for storing their view storages.
+In the `update(_:)` function, update the children's storages.
+An example showcasing how to implement containers is the [VStack][2].
+
+[1]:	https://github.com/JCWasmx86/SwiftGui
+[2]:    ../../Sources/Adwaita/View/VStack.swift